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DO NOT USE THIS PRODUCT IN LIFE SUPPORT SYSTEMS.
LIFE SUPPORT POLICY
ZILOG’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE
SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS PRIOR WRITTEN APPROVAL OF
THE PRESIDENT AND GENERAL COUNSEL OF ZILOG CORPORATION.
As used herein
Life support devices or systems are devices which (a) are intended for surgical implant into the body, or (b)
support or sustain life and whose failure to perform when properly used in accordance with instructions for
use provided in the labeling can be reasonably expected to result in a significant injury to the user. A criti-
cal component is any component in a life support device or system whose failure to perform can be reason-
ably expected to cause the failure of the life support device or system or to affect its safety or effectiveness.
Document Disclaimer
©2016 Zilog, Inc. All rights reserved. Information in this publication concerning the devices, applications,
or technology described is intended to suggest possible uses and may be superseded. ZILOG, INC. DOES
NOT ASSUME LIABILITY FOR OR PROVIDE A REPRESENTATION OF ACCURACY OF THE
INFORMATION, DEVICES, OR TECHNOLOGY DESCRIBED IN THIS DOCUMENT. ZILOG ALSO
DOES NOT ASSUME LIABILITY FOR INTELLECTUAL PROPERTY INFRINGEMENT RELATED
IN ANY MANNER TO USE OF INFORMATION, DEVICES, OR TECHNOLOGY DESCRIBED
HEREIN OR OTHERWISE. The information contained within this document has been verified according
to the general principles of electrical and mechanical engineering.
Z80, Z180, Z380 and Z80382 are trademarks or registered trademarks of Zilog, Inc. All other product or
service names are the property of their respective owners.
Warning:
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User Manual
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Revision History
Each instance in the following revision history table reflects a change to this document
from its previous version. For more details, refer to the corresponding pages provided in
the table.
Date
Revision
Level Description Page
Aug
2016
11 Made formatting changes for better readability. 39
, 40, 41
Aug
2016
10 Added Instruction Notation Summary; corrected typos and
errors
39, 42, 123, 126, 136,
242
,
May
2016
09 Corrected typos and errors. 126
, 132, 133, 136, 141,
192
, 317
Jan
2016
08 Corrected typos and errors. 46, 77, 103, 112, 122,
130
, 132, 138, 161,
207
,221, 224, 227, 233,
253
, 255, 263, 296
Jul
2015
07 Corrected typos in POP qq description. 119
Jul
2014
06 Updated to Zilog style and to incorporate customer
suggestions, including a correction to the Z80 Status
Indicator Flags table, bit 4, and a correction to the EXX
instruction at bit 0.
65
, 126
Feb
2005
05 Corrected the hex code for the RLCA instruction;
corrected illustration for the Rotate and Shift Group RLCA
instruction.
55, 205
Dec
2004
04 Corrected discrepancies in the bit patterns for IM 0, IM 1
and IM 2 instructions.
184, 185, 186
Revision History UM008011-0816
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UM008011-0816 Table of Contents
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Table of Contents
Revision History. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .iii
Table of Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v
List of Figures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi
List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .xiii
Architectural Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
CPU Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Special-Purpose Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
General Purpose Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Arithmetic Logic Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Instruction Register and CPU Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Pin Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Instruction Fetch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Memory Read Or Write . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Input or Output Cycles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Bus Request/Acknowledge Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Interrupt Request/Acknowledge Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Nonmaskable Interrupt Response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
HALT Exit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Power-Down Acknowledge Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Power-Down Release Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Interrupt Response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Interrupt Enable/Disable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
CPU Response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Hardware and Software Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Minimum System Hardware . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Adding RAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Memory Speed Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Interfacing Dynamic Memories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Software Implementation Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Specific Z80 Instruction Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Programming Task Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Z80 CPU Instructions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Instruction Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
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Addressing Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Immediate Addressing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Immediate Extended Addressing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Modified Page Zero Addressing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Relative Addressing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Extended Addressing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Indexed Addressing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Register Addressing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Implied Addressing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Register Indirect Addressing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Bit Addressing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Addressing Mode Combinations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Instruction Notation Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Instruction Op Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Load and Exchange . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Block Transfer and Search . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Arithmetic and Logical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
Rotate and Shift . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
Bit Manipulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Jump, Call, and Return . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
Input/Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
CPU Control Group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
Z80 Instruction Set . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
Z80 Assembly Language . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
Z80 Status Indicator Flags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
Carry Flag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
Add/Subtract Flag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
Decimal Adjust Accumulator Flag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
Parity/Overflow Flag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
Half Carry Flag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
Zero Flag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
Sign Flag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
Z80 Instruction Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
LD r, r' . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
LD r,n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
LD r, (HL) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
LD r, (IX+d) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
LD r, (IY+d) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
LD (HL), r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
LD (IX+d), r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
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LD (IY+d), r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
LD (HL), n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
LD (IX+d), n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
LD (IY+d), n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
LD A, (BC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
LD A, (DE) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
LD A, (nn) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
LD (BC), A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
LD (DE), A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
LD (nn), A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
LD A, I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
LD A, R . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
LD I,A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
LD R, A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
LD dd, nn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
LD IX, nn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
LD IY, nn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
LD HL, (nn) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
LD dd, (nn) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
LD IX, (nn) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
LD IY, (nn) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
LD (nn), HL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
LD (nn), dd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
LD (nn), IX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
LD (nn), IY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
LD SP, HL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
LD SP, IX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
LD SP, IY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
PUSH qq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
PUSH IX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
PUSH IY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
POP qq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
POP IX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
POP IY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
EX DE, HL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
EX AF, AF′ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
EXX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
EX (SP), HL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
EX (SP), IX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
EX (SP), IY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
LDI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
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LDIR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
LDD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134
LDDR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
CPI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
CPIR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
CPD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
CPDR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
ADD A, r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
ADD A, n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
ADD A, (HL) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148
ADD A, (IX + d) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
ADD A, (IY + d) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
ADC A, s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
SUB s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
SBC A, s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
AND s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
OR s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
XOR s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
CP s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163
INC r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165
INC (HL) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167
INC (IX+d) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168
INC (IY+d) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169
DEC m . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170
DAA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173
CPL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175
NEG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176
CCF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178
SCF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
NOP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180
HALT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
DI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182
EI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183
IM 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184
IM 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185
IM 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186
ADD HL, ss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188
ADC HL, ss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
SBC HL, ss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192
ADD IX, pp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194
ADD IY, rr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196
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INC ss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198
INC IX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
INC IY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200
DEC ss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201
DEC IX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202
DEC IY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203
RLCA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205
RLA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
RRCA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209
RRA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211
RLC r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213
RLC (HL) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
RLC (IX+d) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217
RLC (IY+d) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219
RL m . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221
RRC m . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224
RR m . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227
SLA m . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230
SRA m . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233
SRL m . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236
RLD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238
RRD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240
BIT b, r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243
BIT b, (HL) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245
BIT b, (IX+d) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247
BIT b, (IY+d) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249
SET b, r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251
SET b, (HL) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253
SET b, (IX+d) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255
SET b, (IY+d) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257
RES b, m . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259
JP nn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262
JP cc, nn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263
JR e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265
JR C, e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267
JR NC, e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269
JR Z, e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271
JR NZ, e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273
JP (HL) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275
JP (IX) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
JP (IY) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277
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DJNZ, e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278
CALL nn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281
CALL cc, nn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283
RET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285
RET cc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286
RETI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288
RETN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 290
RST p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292
IN A, (n) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295
IN r (C) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296
INI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298
INIR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300
IND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302
INDR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 304
OUT (n), A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306
OUT (C), r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307
OUTI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309
OTIR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311
OUTD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313
OTDR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315
Customer Support. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317
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List of Figures
Figure 1. Z80 CPU Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Figure 2. CPU Register Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Figure 3. Z80 CPU I/O Pin Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Figure 4. Basic CPU Timing Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Figure 5. Instruction Op Code Fetch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Figure 6. Memory Read or Write Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Figure 7. Input or Output Cycles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Figure 8. Bus Request/Acknowledge Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Figure 9. Interrupt Request/Acknowledge Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Figure 10. Nonmaskable Interrupt Request Operation . . . . . . . . . . . . . . . . . . . . . . . . . 14
Figure 11. HALT Exit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Figure 12. Power-Down Acknowledge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Figure 13. Power-Down Release Cycle, #1 of 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Figure 14. Power-Down Release Cycle, #2 of 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Figure 15. Power-Down Release Cycle, #3 of 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Figure 16. Interrupt Enable Flip-Flops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Figure 17. Mode 2 Interrupt Response Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Figure 18. Minimum Z80 Computer System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Figure 19. ROM and RAM Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Figure 20. RAM Memory Space Organization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Figure 21. Adding One Wait State to an M1 Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Figure 22. Adding One Wait State to Any Memory Cycle . . . . . . . . . . . . . . . . . . . . . . 24
Figure 23. Interfacing Dynamic RAM Memory Spaces . . . . . . . . . . . . . . . . . . . . . . . . 25
Figure 24. Shifting of BCD Digits/Bytes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Figure 25. Immediate Addressing Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Figure 26. Immediate Extended Addressing Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Figure 27. Modified Page Zero Addressing Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Figure 28. Relative Addressing Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
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Figure 29. Extended Addressing Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Figure 30. Indexed Addressing Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Figure 31. Register Indirect Addressing Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Figure 32. Example of a 3-Byte Load Indexed Instruction Sequence . . . . . . . . . . . . . 43
Figure 33. Example of a 3-Byte Load Extended Instruction Sequence . . . . . . . . . . . . 44
Figure 34. Example of a 2-Byte Load Immediate Instruction Sequence . . . . . . . . . . . 44
Figure 35. Example of a 4-Byte Load Indexed/Immediate Instruction Sequence . . . . 44
Figure 36. Example of a 16-Bit Load Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Figure 37. Example of a 2-Byte Load Indexed/Immediate Instruction Sequence . . . . 47
Figure 38. Example of an AND Instruction Sequence . . . . . . . . . . . . . . . . . . . . . . . . . 51
Figure 39. Rotates and Shifts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
Figure 40. Example of an Unconditional Jump Sequence . . . . . . . . . . . . . . . . . . . . . . 58
Figure 41. Mode 2 Interrupt Command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
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List of Tables
Table 1. Interrupt Enable/Disable, Flip-Flops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Table 2. Bubble Listing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Table 3. Multiply Listing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Table 4. Instruction Notation Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Table 5. Hex, Binary, Decimal Conversion Table . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Table 6. 8-Bit Load Group LD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Table 7. 16-Bit Load Group LD, PUSH, and POP . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Table 8. Exchanges EX and EXX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Table 9. Block Transfer Group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
Table 10. Block Search Group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
Table 11. 8-Bit Arithmetic and Logic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
Table 12. General-Purpose AF Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Table 13. 16-Bit Arithmetic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Table 14. Bit Manipulation Group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Table 15. Jump, Call, and Return Group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
Table 16. Example Usage of the DJNZ Instruction . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
Table 17. Restart Group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
Table 18. Input Group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
Table 19. 8-Bit Arithmetic and Logic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
Table 20. Miscellaneous CPU Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
Table 21. Flag Register Bit Positions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
Table 22. Flag Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
Table 23. Half Carry Flag Add/Subtract Operations . . . . . . . . . . . . . . . . . . . . . . . . . . 68
List of Tables UM008011-0816
xiv
Z80 CPU
User Manual
UM008011-0816 Architectural Overview
Z80 CPU
User Manual
1
Architectural Overview
Zilog’s Z80 CPU family of components are fourth-generation enhanced microprocessors
with exceptional computational power. They offer higher system throughput and more
efficient memory utilization than comparable second and third-generation microproces-
sors. The speed offerings from 6–20 MHz suit a wide range of applications which migrate
software. The internal registers contain 208 bits of read/write memory that are accessible
to the programmer. These registers include two sets of six general-purpose registers which
can be used individually as either 8-bit registers or as 16-bit register pairs. In addition,
there are two sets of Accumulator and Flag registers.
The Z80 CPU also contains a Stack Pointer, Program Counter, two index registers, a
refresh register, and an interrupt register. The CPU is easy to incorporate into a system
because it requires only a single +5V power source. All output signals are fully decoded
and timed to control standard memory or peripheral circuits; the Z80 CPU is supported by
an extensive family of peripheral controllers.
Figure 1 shows the internal architecture and major elements of the Z80 CPU.
Figure 1. Z80 CPU Block Diagram
13
CPU and
System
Control
Signals
Inst.
Register
Data Bus
Control
Internal Data Bus
CPU
Registers
ALU
CPU
Control
Address
Control
16-Bit
Address Bus
+5V GND CLK
I
n
Architectural Overview UM008011-0816
2
Z80 CPU
User Manual
CPU Register
The Z80 CPU contains 208 bits of read/write memory that are available to the program-
mer. Figure 2 shows how this memory is configured to eighteen 8-bit registers and four
16-bit registers. All Z80 CPU’s registers are implemented using static RAM. The registers
include two sets of six general-purpose registers that can be used individually as 8-bit reg-
isters or in pairs as 16-bit registers. There are also two sets of Accumulator and Flag regis-
ters and six special-purpose registers.
Special-Purpose Registers
Program Counter (PC). The program counter holds the 16-bit address of the current
instruction being fetched from memory. The Program Counter is automatically incre-
mented after its contents are transferred to the address lines. When a program jump occurs,
the new value is automatically placed in the Program Counter, overriding the incrementer.
Stack Pointer (SP). The stack pointer holds the 16-bit address of the current top of a stack
located anywhere in external system RAM memory. The external stack memory is orga-
nized as a last-in first-out (LIFO) file. Data can be pushed onto the stack from specific
CPU registers or popped off of the stack to specific CPU registers through the execution of
PUSH and POP instructions. The data popped from the stack is always the most recent
data pushed onto it. The stack allows simple implementation of multiple level interrupts,
unlimited subroutine nesting and simplification of many types of data manipulation.
Figure 2. CPU Register Configuration
General
Purpose
Registers
Accumulator
H '
Special
Purpose
Registers
Index Register
Index Register
Stack Pointer
Program Counter
Interrupt Vector
I
HL L '
DED 'E '
BCB 'B '
A
F
A '
F '
Flags Accumulator Flags
Alternate Register SetMain Register Set
Memory Refresh
R
IX
IY
SP
PC
UM008011-0816 General Purpose Registers
Z80 CPU
User Manual
3
Two Index Registers (IX and IY). The two independent index registers hold a 16-bit base
address that is used in indexed addressing modes. In this mode, an index register is used as
a base to point to a region in memory from which data is to be stored or retrieved. An addi-
tional byte is included in indexed instructions to specify a displacement from this base.
This displacement is specified as a two’s complement signed integer. This mode of
addressing greatly simplifies many types of programs, especially when tables of data are
used.
Interrupt Page Address (I) Register. The Z80 CPU can be operated in a mode in which
an indirect call to any memory location can be achieved in response to an interrupt. The I
register is used for this purpose and stores the high-order eight bits of the indirect address
while the interrupting device provides the lower eight bits of the address. This feature
allows interrupt routines to be dynamically located anywhere in memory with minimal
access time to the routine.
Memory Refresh (R) Register. The Z80 CPU contains a memory refresh counter,
enabling dynamic memories to be used with the same ease as static memories. Seven bits
of this 8-bit register are automatically incremented after each instruction fetch. The eighth
bit remains as programmed, resulting from an LD R, A instruction. The data in the refresh
counter is sent out on the lower portion of the address bus along with a refresh control sig-
nal while the CPU is decoding and executing the fetched instruction. This mode of refresh
is transparent to the programmer and does not slow the CPU operation. The programmer
can load the R register for testing purposes, but this register is normally not used by the
programmer. During refresh, the contents of the I Register are placed on the upper eight
bits of the address bus.
Accumulator and Flag Registers. The CPU includes two independent 8-bit Accumula-
tors and associated 8-bit Flag registers. The Accumulator holds the results of 8-bit arith-
metic or logical operations while the Flag Register indicates specific conditions for 8-bit
or 16-bit operations, such as indicating whether or not the result of an operation is equal to
0. The programmer selects the Accumulator and flag pair with a single exchange instruc-
tion so that it is possible to work with either pair.
General Purpose Registers
Two matched sets of general-purpose registers, each set containing six 8-bit registers, can
be used individually as 8-bit registers or as 16-bit register pairs. One set is called BC, DE,
and HL while the complementary set is called BC', DE', and HL'. At any one time, the pro-
grammer can select either set of registers to work through a single exchange command for
the entire set. In systems that require fast interrupt response, one set of general-purpose
registers and an Accumulator/Flag Register can be reserved for handling this fast routine.
One exchange command is executed to switch routines. This process greatly reduces inter-
rupt service time by eliminating the requirement for saving and retrieving register contents
in the external stack during interrupt or subroutine processing. These general-purpose reg-
Architectural Overview UM008011-0816
4
Z80 CPU
User Manual
isters are used for a wide range of applications. They also simplify programing, specifi-
cally in ROM-based systems in which little external read/write memory is available.
Arithmetic Logic Unit
The 8-bit arithmetic and logical instructions of the CPU are executed in the Arithmetic
Logic Unit (ALU). Internally, the ALU communicates with the registers and the external
data bus by using the internal data bus. Functions performed by the ALU include:
• Add
• Subtract
• Logical AND
• Logical OR
• Logical exclusive OR
• Compare
• Left or right shifts or rotates (arithmetic and logical)
• Increment
• Decrement
• Set bit
• Reset bit
• Test bit
Instruction Register and CPU Control
As each instruction is fetched from memory, it is placed in the Instruction Register and
decoded. The control sections performs this function and then generates and supplies the
control signals necessary to read or write data from or to the registers, control the ALU,
and provide required external control signals.
Pin Description
The Z80 CPU I/O pins are shown in Figure 3. The function of each pin is described in the
section that follows.
UM008011-0816 Pin Functions
Z80 CPU
User Manual
5
Pin Functions
A15–A0. Address Bus (output, active High, tristate). A15–A0 form a 16-bit Address Bus,
which provides the addresses for memory data bus exchanges (up to 64 KB) and for I/O
device exchanges.
BUSACK. Bus Acknowledge (output, active Low). Bus Acknowledge indicates to the
requesting device that the CPU address bus, data bus, and control signals MREQ
, IORQ,
Figure 3. Z80 CPU I/O Pin Configuration
System
Control
CPU
Control
CPU
Bus
Control
Z80 CPU
Address
Bus
Data
Bus
A0
A1
A2
A3
A4
A5
A6
A7
A8
A9
A10
A11
A12
A13
A14
A15
D0
D1
D3
D4
D5
D6
D7
D2
30
31
32
33
34
35
36
37
38
39
40
14
15
12
8
7
9
10
13
1
2
3
4
5
M1
MREQ
IORQ
RD
WR
RFSH
HALT
INT
NMI
RESET
BUSRQ
BUSACK
CLK
+5V
GND
WAIT
27
19
20
21
22
26
18
24
16
17
28
25
23
6
11
29
Architectural Overview UM008011-0816
6
Z80 CPU
User Manual
RD, and WR have entered their high-impedance states. The external circuitry can now
control these lines.
BUSREQ. Bus Request (input, active Low). Bus Request contains a higher priority than
NMI
and is always recognized at the end of the current machine cycle. BUSREQ forces
the CPU address bus, data bus, and control signals MREQ
, IORQ, RD, and WR to enter a
high-impedance state so that other devices can control these lines. BUSREQ
is normally
wired OR and requires an external pull-up for these applications. Extended BUSREQ
peri-
ods due to extensive DMA operations can prevent the CPU from properly refreshing
dynamic RAM.
D7–D0. Data Bus (input/output, active High, tristate). D7–D0 constitute an 8-bit bidirec-
tional data bus, used for data exchanges with memory and I/O.
HALT. HALT State (output, active Low). HALT indicates that the CPU has executed a
HALT instruction and is waiting for either a nonmaskable or a maskable interrupt (with
the mask enabled) before operation can resume. During HALT, the CPU executes NOPs to
maintain memory refreshes.
INT. Interrupt Request (input, active Low). An Interrupt Request is generated by I/O
devices. The CPU honors a request at the end of the current instruction if the internal soft-
ware-controlled interrupt enable flip-flop (IFF) is enabled. INT
is normally wired-OR and
requires an external pull-up for these applications.
IORQ. Input/Output Request (output, active Low, tristate). IORQ indicates that the lower
half of the address bus holds a valid I/O address for an I/O read or write operation. IORQ
is also generated concurrently with M1
during an interrupt acknowledge cycle to indicate
that an interrupt response vector can be placed on the data bus.
M1. Machine Cycle One (output, active Low). M1, together with MREQ, indicates that the
current machine cycle is the op code fetch cycle of an instruction execution. M1
, when
operating together with IORQ
, indicates an interrupt acknowledge cycle.
MREQ. Memory Request (output, active Low, tristate). MREQ indicates that the address
bus holds a valid address for a memory read or a memory write operation.
NMI. Nonmaskable Interrupt (input, negative edge-triggered). NMI contains a higher pri-
ority than INT
. NMI is always recognized at the end of the current instruction, indepen-
dent of the status of the interrupt enable flip-flop, and automatically forces the CPU to
restart at location
0066h.
RD. Read (output, active Low, tristate). RD indicates that the CPU wants to read data from
memory or an I/O device. The addressed I/O device or memory should use this signal to
gate data onto the CPU data bus.
RESET. Reset (input, active Low). RESET initializes the CPU as follows: it resets the
interrupt enable flip-flop, clears the Program Counter and registers I and R, and sets the
interrupt status to Mode 0. During reset time, the address and data bus enter a high-imped-
ance state, and all control output signals enter an inactive state. R
ESET must be active for
a minimum of three full clock cycles before a reset operation is complete.
UM008011-0816 Timing
Z80 CPU
User Manual
7
RFSH. Refresh (output, active Low). RFSH, together with MREQ, indicates that the lower
seven bits of the system’s address bus can be used as a refresh address to the system’s
dynamic memories.
WAIT. WAIT (input, active Low). WA IT communicates to the CPU that the addressed
memory or I/O devices are not ready for a data transfer. The CPU continues to enter a
WA IT
state as long as this signal is active. Extended WAIT periods can prevent the CPU
from properly refreshing dynamic memory.
WR. Write (output, active Low, tristate). WR indicates that the CPU data bus contains
valid data to be stored at the addressed memory or I/O location.
CLK. Clock (input). Single-phase MOS-level clock.
All signals with an overline are active Low. For example, B/W, in which word is active
Low, or B/W, in which byte is active Low.
Timing
The Z80 CPU executes instructions by stepping through a precise set of basic operations.
These operations include:
• Memory read or write
• I/O device read or write
• Interrupt acknowledge
All instructions are a series of basic operations. Each of these operations can take from
three to six clock periods to complete, or they can be lengthened to synchronize the CPU
to the speed of external devices. These clock periods are referred to as time (T) cycles, and
the operations are referred to as machine (M) cycles. Figure 4 shows how a typical instruc-
tion is a series of specific M and T cycles. In Figure 4, this instruction consists of the three
machine cycles M1, M2, and M3. The first machine cycle of any instruction is a fetch
cycle that is four, five, or six T cycles long (unless lengthened by the WAIT signal, which
is described in the next section). The fetch cycle (M1) is used to fetch the op code of the
next instruction to be executed. Subsequent machine cycles move data between the CPU
and memory or I/O devices, and they can feature anywhere from three to five T cycles
(again, they can be lengthened by wait states to synchronize external devices to the CPU).
The following paragraphs describe the timing which occurs within any of the basic
machine cycles.
During T2 and every subsequent automatic WAIT state (TW), the CPU samples the WAIT
line with the falling edge of the clock. If the WAIT line is active at this time, another
Note:
Architectural Overview UM008011-0816
8
Z80 CPU
User Manual
WAIT state is entered during the following cycle. Using this technique, the read can be
lengthened to match the access time of any type of memory device. See the Input or Out-
put Cycles section on page 10 to learn more about the automatic WAIT state.
Instruction Fetch
Figure 5 depicts the timing during an M1 (op code fetch) cycle. The Program Counter is
placed on the address bus at the beginning of the M1 cycle. One half clock cycle later, the
MREQ
signal goes active. At this time, the address to memory has had time to stabilize so
that the falling edge of MREQ
can be used directly as a chip enable clock to dynamic
memories. The RD
line also goes active to indicate that the memory read data should be
enabled onto the CPU data bus. The CPU samples the data from the memory space on the
data bus with the rising edge of the clock of state T3, and this same edge is used by the
CPU to turn off the RD
and MREQ signals. As a result, the data is sampled by the CPU
before the RD
signal becomes inactive. Clock states T3 and T4 of a fetch cycle are used to
refresh dynamic memories. The CPU uses this time to decode and execute the fetched
instruction so that no other concurrent operation can be performed.
During T3 and T4, the lower seven bits of the address bus contain a memory refresh
address and the RFSH
signal becomes active, indicating that a refresh read of all dynamic
memories must be performed. To prevent data from different memory segments from
being gated onto the data bus, an RD
signal is not generated during this refresh period. The
MREQ
signal during this refresh period should be used to perform a refresh read of all
memory elements. The refresh signal cannot be used by itself, because the refresh address
is only guaranteed to be stable during the M
REQ period.
Figure 4. Basic CPU Timing Example
CLK
T Cycle
Machine Cycle
M1
(Opcode Fetch)
Instruction Cycle
M2
(Memory Read)
M3
(Memory Write)
T1 T1 T1T2 T2 T2T3 T3 T3
UM008011-0816 Memory Read Or Write
Z80 CPU
User Manual
9
Memory Read Or Write
Figure 6 shows the timing of memory read or write cycles other than an op code fetch
cycle. These cycles are generally three clock periods long unless wait states are requested
by memory through the WAIT
signal. The MREQ signal and the RD signal are used the
same way as in a fetch cycle. In a memory write cycle, the MREQ
also becomes active
when the address bus is stable so that it can be used directly as a chip enable for dynamic
memories. The WR
line is active when the data on the data bus is stable so that it can be
used directly as a R/W pulse to virtually any type of semiconductor memory. Furthermore,
the WR
signal goes inactive one-half T state before the address and data bus contents are
changed so that the overlap requirements for almost any type of semiconductor memory
type is met.
Figure 5. Instruction Op Code Fetch
PC
Refresh Address
M1 Cycle
CLK
MREQ
RD
WAIT
M1
RFSH
IN
D7–D0
A15 –A0
T2 T4 T1T1 T3
Architectural Overview UM008011-0816
10
Z80 CPU
User Manual
Input or Output Cycles
Figure 7 shows an I/O read or I/O write operation. During I/O operations, a single wait
state is automatically inserted. The reason for this single wait state insertion is that during
I/O operations, the period from when the IORQ
signal goes active until the CPU must
sample the WAIT
line is short. Without this extra state, sufficient time does not exist for an
I/O port to decode its address and activate the WAIT
line if a wait is required. Addition-
ally, without this wait state, it is difficult to design MOS I/O devices that can operate at
full CPU speed. During this wait state period, the WAIT
request signal is sampled.
During a read I/O operation, the RD
line is used to enable the addressed port onto the data
bus, just as in the case of a memory read. The WR
line is used as a clock to the I/O port for
write operations.
Figure 6. Memory Read or Write Cycle
CLK
D7–D0
A15 –A0
MREQ
RD
WAIT
WR
Memory AddressMemory Address
T2 T3 T1 T2
T3
In
Memory Read Cycle
Memory Write Cycle
Data Out
UM008011-0816 Bus Request/Acknowledge Cycle
Z80 CPU
User Manual
11
*In Figure 7, TW is an automatically-inserted WAIT state.
Bus Request/Acknowledge Cycle
Figure 8 shows the timing for a Bus Request/Acknowledge cycle. The BUSREQ signal is
sampled by the CPU with the rising edge of the most recent clock period of any machine
cycle. If the BUSREQ
signal is active, the CPU sets its address, data, and tristate control
signals to the high-impedance state with the rising edge of the next clock pulse. At that
time, any external device can control the buses to transfer data between memory and I/O
devices. (This operation is generally known as Direct Memory Access [DMA] using cycle
stealing.) The maximum time for the CPU to respond to a bus request is the length of a
machine cycle and the external controller can maintain control of the bus for as many
clock cycles as is required. If long DMA cycles are used, and dynamic memories are used,
the external controller also performs the refresh function. This situation only occurs if
Figure 7. Input or Output Cycles
Out
TW*
Write
Cycle
Read
Cycle
Port Address
CLK
IORQ
RD
WAIT
WR
In
D7–D0
A15 –A0
D7–D0
T1 T2 T3 T1
Note:
Architectural Overview UM008011-0816
12
Z80 CPU
User Manual
large blocks of data are transferred under DMA control. During a bus request cycle, the
CPU cannot be interrupted by either an NMI
or an INT signal.
Interrupt Request/Acknowledge Cycle
Figure 9 shows the timing associated with an interrupt cycle. The CPU samples the inter-
rupt signal (INT)
with the rising edge of the final clock at the end of any instruction. The
signal is not accepted if the internal CPU software controlled interrupt enable flip-flop is
not set or if the BUSREQ
signal is active. When the signal is accepted, a special M1 cycle
is generated. During this special M1 cycle, the IORQ
signal becomes active (instead of the
normal MREQ)
to indicate that the interrupting device can place an 8-bit vector on the
data bus. Two wait states are automatically added to this cycle. These states are added so
that a ripple priority interrupt scheme can be easily implemented. The two wait states
allow sufficient time for the ripple signals to stabilize and identify which I/O device must
insert the response vector. Refer to the Interrupt Response
section on page 17 to learn
more about how the interrupt response vector is utilized by the CPU.
Figure 8. Bus Request/Acknowledge Cycle
Sample
Sample
Floating
Last T State
Tx
Tx
Tx
T1
Any M Cycle
Bus Available Status
CLK
BUSREQ
MREQ, RD
BUSACK
WR. IORQ,
RFSH
A15 –A0
D7–D0
UM008011-0816 Nonmaskable Interrupt Response
Z80 CPU
User Manual
13
Nonmaskable Interrupt Response
Figure 10 shows the request/acknowledge cycle for the nonmaskable interrupt. This signal
is sampled at the same time as the interrupt line, but this line takes priority over the normal
interrupt and it cannot be disabled under software control. Its usual function is to provide
immediate response to important signals such as an impending power failure. The CPU
response to a nonmaskable interrupt is similar to a normal memory read operation. The
only difference is that the contents of the data bus are ignored while the processor auto-
matically stores the Program Counter in the external stack and jumps to address
0066h.
The service routine for the nonmaskable interrupt must begin at this location if this inter-
rupt is used.
Figure 9. Interrupt Request/Acknowledge Cycle
In
Refresh
PC
M1
Last M Cycle of Instruction
CLK
INT
MREQ
RD
WAIT
M1
IORQ
Last T State
A15 –A0
D7–D0
TW* TW*
T1 T2 T3
Architectural Overview UM008011-0816
14
Z80 CPU
User Manual
HALT Exit
When a software HALT instruction is executed, the CPU executes NOPs until an interrupt
is received (either a nonmaskable or a maskable interrupt while the interrupt flip-flop is
enabled). The two interrupt lines are sampled with the rising clock edge during each T4
state as depicted in Figure 11. If a nonmaskable interrupt is received or a maskable inter-
rupt is received and the interrupt enable flip-flop is set, then the HALT state is exited on
the next rising clock edge. The following cycle is an interrupt acknowledge cycle corre-
sponding to the type of interrupt that was received. If both are received at this time, then
the nonmaskable interrupt is acknowledged because it is the highest priority. The purpose
of executing NOP instructions while in the HALT state is to keep the memory refresh sig-
nals active. Each cycle in the HALT state is a normal M1 (fetch) cycle except that the data
received from the memory is ignored and an NOP instruction is forced internally to the
CPU. The HALT acknowledge signal is active during this time indicating that the proces-
sor is in the HALT state.
Figure 10. Nonmaskable Interrupt Request Operation
CLK
NMI
MREQ
RD
RFSH
M1
Refresh
M1Last M Cycle
Last T State
PC
A15 –A0
T3
T1 T2 T4 T1
UM008011-0816 Power-Down Acknowledge Cycle
Z80 CPU
User Manual
15
The HALT instruction is repeated during the memory cycle shown in Figure 11.
Power-Down Acknowledge Cycle
When the clock input to the Z80 CPU is stopped at either a High or Low level, the Z80
CPU stops its operation and maintains all registers and control signals. However, ICC2
(standby supply current) is guaranteed only when the system clock is stopped at a Low
level during T4 of the machine cycle following the execution of the HALT instruction.
The timing diagram for the power-down function (when implemented with the HALT
instruction) is shown in Figure 12.
Figure 11. HALT Exit
Figure 12. Power-Down Acknowledge
CLK
RD or
HALT
M1
NMI
M1
T2
T4 T1 T3 T4 T1 T2
Note:
CLK
HALT
M1
T3
T1 T2 T4
T3
T2 T4T1
Architectural Overview UM008011-0816
16
Z80 CPU
User Manual
Power-Down Release Cycle
The system clock must be supplied to the Z80 CPU to release the power-down state. When
the system clock is supplied to the CLK input, the Z80 CPU restarts operations from the
point at which the power-down state was implemented. The timing diagrams for the
release from power-down mode are featured in Figures 13 through 15. When the HALT
instruction is executed to enter the power-down state, the Z80 CPU also enters the HALT
state. An interrupt signal (either NMI
or ANT) or a RESET signal must be applied to the
CPU after the system clock is supplied to release the power-down state.
Figure 13. Power-Down Release Cycle, #1 of 3
Figure 14. Power-Down Release Cycle, #2 of 3
CLK
HALT
T1 T2 T3 T1
M1
T4
NMI
CLK
HALT
T1 T2 T3
M1
T4
RESET
UM008011-0816 Interrupt Response
Z80 CPU
User Manual
17
Interrupt Response
An interrupt allows peripheral devices to suspend CPU operation and force the CPU to
start a peripheral service routine. This service routine usually involves the exchange of
data, status, or control information between the CPU and the peripheral. When the service
routine is completed, the CPU returns to the operation from which it was interrupted.
Interrupt Enable/Disable
The Z80 CPU contains two interrupt inputs: a software maskable interrupt (INT) and a
nonmaskable interrupt (NMI
). The nonmaskable interrupt cannot be disabled by the pro-
grammer and is accepted when a peripheral device requests it. This interrupt is generally
reserved for important functions that can be enabled or disabled selectively by the pro-
grammer. This routine allows the programmer to disable the interrupt during periods when
the program contains timing constraints that wont allow interrupt. In the Z80 CPU, there is
an interrupt enable flip-flop (IFF) that is set or reset by the programmer using the Enable
Interrupt (EI) and Disable Interrupt (DI) instructions. When the IFF is reset, an interrupt
cannot be accepted by the CPU.
The two enable flip-flops are IFF1 and IFF2, as depicted in Figure 16.
Figure 15. Power-Down Release Cycle, #3 of 3
Figure 16. Interrupt Enable Flip-Flops
CLK
HALT
T1 T2 T3
M1
T4
INT
T1 T2 TWA TWA
IFF1
IFF2
Disables interrupts
from being accepted
Temporary storage
location for IFF1
Architectural Overview UM008011-0816
18
Z80 CPU
User Manual
The state of IFF1 is used to inhibit interrupts while IFF2 is used as a temporary storage
location for IFF1.
A CPU reset forces both the IFF1 and IFF2 to the reset state, which disables interrupts.
Interrupts can be enabled at any time by an EI instruction from the programmer. When an
EI instruction is executed, any pending interrupt request is not accepted until after the
instruction following EI is executed. This single instruction delay is necessary when the
next instruction is a return instruction. Interrupts are not allowed until a return is com-
pleted. The EI instruction sets both IFF1 and IFF2 to the enable state. When the CPU
accepts a maskable interrupt, both IFF1 and IFF2 are automatically reset, inhibiting fur-
ther interrupts until the programmer issues a new El instruction.
For all of the previous cases, IFF1 and IFF2 are always equal.
The purpose of IFF2 is to save the status of IFF1 when a nonmaskable interrupt occurs.
When a nonmaskable interrupt is accepted, IFF1 resets to prevent further interrupts until
reenabled by the programmer. Therefore, after a nonmaskable interrupt is accepted, mask-
able interrupts are disabled but the previous state of IFF1 is saved so that the complete
state of the CPU just prior to the nonmaskable interrupt can be restored at any time. When
a Load Register A with Register I (LD A, I) instruction or a Load Register A with Register
R (LD A, R) instruction is executed, the state of IFF2 is copied to the parity flag, where it
can be tested or stored.
A second method of restoring the status of IFF1 is through the execution of a Return From
Nonmaskable Interrupt (RETN) instruction. This instruction indicates that the nonmask-
able interrupt service routine is complete and the contents of IFF2 are now copied back
into IFF1 so that the status of IFF1 just prior to the acceptance of the nonmaskable inter-
rupt is restored automatically.
Table 1 is a summary of the effect of different instructions on the two enable flip-flops.
Table 1. Interrupt Enable/Disable, Flip-Flops
Action IFF1 IFF2 Comments
CPU Reset 0 0 Maskable interrupt, INT
disabled.
DI Instruction Execution 0 0 Maskable INT
disabled.
EI Instruction Execution 1 1 Maskable, INT
enabled.
LD A,I Instruction
Execution
**IFF2 → Parity flag.
LD A,R instruction
Execution
**IFF2 → Parity flag.
Note:
UM008011-0816 CPU Response
Z80 CPU
User Manual
19
CPU Response
The CPU always accepts a nonmaskable interrupt. When this nonmaskable interrupt is
accepted, the CPU ignores the next instruction that it fetches and instead performs a restart
at address
0066h. The CPU functions as if it had recycled a restart instruction, but to a
location other than one of the eight software restart locations. A restart is merely a call to a
specific address in Page 0 of memory.
The CPU can be programmed to respond to the maskable interrupt in any one of three pos-
sible modes.
Mode 0
Mode 0 is similar to the 8080A interrupt response mode. With Mode 0, the interrupting
device can place any instruction on the data bus and the CPU executes it. Consequently,
the interrupting device provides the next instruction to be executed. Often this response is
a restart instruction because the interrupting device is required to supply only a single-byte
instruction. Alternatively, any other instruction such as a 3-byte call to any location in
memory could be executed.
The number of clock cycles necessary to execute this instruction is two more than the nor-
mal number for the instruction. The addition of two clock cycles occurs because the CPU
automatically adds two wait states to an Interrupt response cycle to allow sufficient time to
implement an external daisy-chain for priority control. Figures 9 and 10
on page 13 show
the timing for an interrupt response. After the application of RESET
, the CPU automati-
cally enters interrupt Mode 0.
Mode 1
When Mode 1 is selected by the programmer, the CPU responds to an interrupt by execut-
ing a restart at address
0038h. As a result, the response is identical to that of a nonmask-
able interrupt except that the call location is
0038h instead of 0066h. The number of
cycles required to complete the restart instruction is two more than normal due to the two
added wait states.
Mode 2
Mode 2 is the most powerful interrupt response mode. With a single 8-bit byte from the
user, an indirect call can be made to any memory location.
Accept NMI 0 * Maskable → Interrupt.
RETN Instruction
Execution
IFF2 * IFF2 → Indicates completion of
nonmaskable interrupt service routine.
Table 1. Interrupt Enable/Disable, Flip-Flops (Continued)
Action IFF1 IFF2 Comments
Architectural Overview UM008011-0816
20
Z80 CPU
User Manual
In Mode 2, the programmer maintains a table of 16-bit starting addresses for every inter-
rupt service routine. This table can be located anywhere in memory. When an interrupt is
accepted, a 16-bit pointer must be formed to obtain the required interrupt service routine
starting address from the table. The upper eight bits of this pointer is formed from the con-
tents of the I Register. The I register must be loaded with the applicable value by the pro-
grammer, such as LD I, A. A CPU reset clears the I Register so that it is initialized to 0.
The lower eight bits of the pointer must be supplied by the interrupting device. Only seven
bits are required from the interrupting device, because the least-significant bit must be a 0.
This process is required, because the pointer must receive two adjacent bytes to form a
complete 16-bit service routine starting address; addresses must always start in even loca-
tions.
The first byte in the table is the least-significant (low-order portion of the address). The
programmer must complete the table with the correct addresses before any interrupts are
accepted.
The programmer can change the table by storing it in read/write memory, which also
allows individual peripherals to be serviced by different service routines.
When the interrupting device supplies the lower portion of the pointer, the CPU automati-
cally pushes the program counter onto the stack, obtains the starting address from the
table, and performs a jump to this address. This mode of response requires 19 clock peri-
ods to complete (seven to fetch the lower eight bits from the interrupting device, six to
save the program counter, and six to obtain the jump address).
The Z80 peripheral devices include a daisy-chain priority interrupt structure that automat-
ically supplies the programmed vector to the CPU during interrupt acknowledge. Refer to
the Z80 CPU Peripherals User Manual (UM0081)
for more complete information.
Figure 17. Mode 2 Interrupt Response Mode
Starting Address
Pointed to by:
I Register
Contents
Seven Bits From
Peripheral
0
Low Order
High Order
Interrupt
Service
Routine
Starting
Address
Table
UM008011-0816 Hardware and Software Implementation
Z80 CPU
User Manual
21
Hardware and Software Implementation
This chapter is an introduction to implementing systems that use the Z80 CPU. Figure 18
shows a simple Z80 system.
Minimum System Hardware
Any Z80 system must include the following hardware elements:
• 5 V power supply
• Oscillator
• Memory devices
• I/O circuits
• CPU
Figure 18. Minimum Z80 Computer System
RESET
+5V
Z80
CPU
M1
IORQ
Data Bus
RD
MREQ
A
9
–A
0
+5V
Data
OUT
GND
Address
IN
+5V Power Supply
CLK
A
0
A
1
M1
IORQ
CE
RD
Output Data
OSC
CLK
Input Data
C/D
B/A
Z80-PIO
Port A Port B
CE1
CE2
ROM
8K Bit
Hardware and Software Implementation UM008011-0816
22
Z80 CPU
User Manual
Because the Z80 CPU requires only a single 5 V power supply, most small systems can be
implemented using only this single supply.
The external memory can be any mixture of standard RAM, ROM, or PROM. In Fig-
ure 18, a single 8 Kb (1 KB) ROM comprises the entire memory system. The Z80 internal
register configuration contains sufficient read/write storage, requiring no external RAM
memory.
I/O circuits allow computer systems to interface with the external devices. In Figure 18,
the output is an 8-bit control vector and the input is an 8-bit status word. The input data
can be gated to the data bus using any standard three-state driver while the output data can
be latched with any type of standard TTL latch. A Z80 PIO serves as the I/O circuit. This
single circuit attaches to the data bus as indicated and provides the required 16 bits of
TTL-compatible I/O. Refer to the Z80 CPU Peripherals User Manual (UM0081)
to learn
more about the operation of this circuit. This powerful computer is built with only three
LSI circuits, a simple oscillator, and a single 5V power supply.
Adding RAM
Most computer systems require some external read/write memory for data storage and
stack implementation. Figure 19 shows how 256 bytes of static memory are added to the
example shown in Figure 18.
The memory space is assumed to be organized as shown in Figure 20.
Figure 19. ROM and RAM Implementation
CE1
CE2
ROM
1K x 8
MREQ • RD
A
10
A
7
–A
0
D
7
–D
0
WR
RD
R/W
OD
CE2
A
10
A
7
–A
0
D
3
–D
0
CE1
WR
RD
R/W
OD
MRQ
Data Bus
D
7
–D
4
Address Bus
A
7
–A
0
RAM
256 x 4
RAM
256 x 4
A
10
MRQ
CE2
CE1
UM008011-0816 Memory Speed Control
Z80 CPU
User Manual
23
In Figure 20, the address space is portrayed in hexadecimal notation. Address bit A10 sep-
arates the ROM space from the RAM space, allowing this address to be used for the chip
select function. For larger amounts of external ROM or RAM, a simple TTL decoder is
required to form the chip selects.
Memory Speed Control
Slow memories can reduce costs for many applications. The WAIT line on the CPU allows
the Z80 to operate with any speed memory. Memory access time requirements, which are
covered in the Memory Read Or Write
section on page 9, are most severe during the M1
cycle instruction fetch. All other memory access cycles complete in an additional one half
clock cycle. Hence, it is sometimes appropriate to add one wait state to the M1
cycle so
slower memories can be used.
Figure 21 is an example of a simple circuit that accomplishes this objective. This circuit
can be changed to add a single wait state to any memory access, as indicated in Figure 22.
Figure 20. RAM Memory Space Organization
1 Kbyte ROM
Address:
0000h
03FFh
0400h
04FFFh
256 Bytes RAM
Hardware and Software Implementation UM008011-0816
24
Z80 CPU
User Manual
Figure 21. Adding One Wait State to an M1 Cycle
Figure 22. Adding One Wait State to Any Memory Cycle
+5V
D
C
Q
Q
R
S
7474
+5V
D
C
Q
Q
R
S
7474
+5V
M1
CLK
WAIT
CLK
M1
WAIT
M1
T
1
T
2
T
W
T
3
T
4
+5V
D
C
Q
Q
R
S
7474
+5V
D
C
Q
Q
R
S
7474
+5V
MREQ
CLK
+5V
7400
WAIT
WAIT
MREQ
CLK
T
1
T
2
T
W
UM008011-0816 Interfacing Dynamic Memories
Z80 CPU
User Manual
25
Interfacing Dynamic Memories
Each individual dynamic RAM space includes its own specifications that require minor
modifications to the examples provided here.
Figure 23 shows the logic necessary to interface 8 KB of dynamic RAM using 18-pin 4K
dynamic memories. This logic assumes that the RAMs are the only memory in the system
so that A12 is used to select between the two pages of memory. During refresh time, all
memories in the system must be read. The CPU provides the correct refresh address on
lines A0 through A6. When adding more memory to the system, it is necessary to replace
only the two gates that operate on A12 with a decoder that operates on all required address
bits. Address buffers and data bus buffers are generally required for larger systems.
Figure 23. Interfacing Dynamic RAM Memory Spaces
WR
R/W
R/W
CE
CE
4K x 8 RAM Array
Page 0
(0000 to 0FFFF)
4K x 8 RAM Array
Data Bus
Page 1
(1000 to 1FFFF)
D
7
–D
0
A
11
–A
0
RFSH
MREQ
A
12
Hardware and Software Implementation UM008011-0816
26
Z80 CPU
User Manual
Software Implementation Examples
The Z80 instruction set provides the user with a large number of operations to control the
Z80 CPU. The main alternate and index registers can hold arithmetic and logical opera-
tions, form memory addresses, or act as fast-access storage for frequently used data.
Information can be moved directly from register to register, memory to memory, memory
to registers, or from registers to memory. In addition, register contents and register/mem-
ory contents can be exchanged without using temporary storage. In particular, the contents
of main and alternate registers can be completely exchanged by executing only two
instructions, EX and EXX. This register exchange procedure can be used to separate the
set of working registers from different logical procedures or to expand the set of available
registers in a single procedure.
Storage and retrieval of data between pairs of registers and memory can be controlled on a
last-in first-out basis through PUSH and POP instructions that utilize a special Stack
Pointer (SP) Register. This stack register is available both to manipulate data and to auto-
matically store and retrieve addresses for subroutine linkage. When a subroutine is called,
for example, the address following the CALL instruction is placed on the top of the push-
down stack pointed to by SP. When a subroutine returns to the calling routine, the address
on the top of the stack is used to set the program counter for the address of the next
instruction. The stack pointer is adjusted automatically to reflect the current top stack
position during PUSH, POP, CALL, and RET instructions. This stack mechanism allows
pushdown data stacks and subroutine calls to be nested to any practical depth because the
stack area can potentially be as large as memory space.
The sequence of instruction execution can be controlled by six different flags (carry, zero,
sign, parity/overflow, add/subtract, half-carry), which reflect the results of arithmetic, log-
ical, shift, and compare instructions. After the execution of an instruction that sets a flag,
that flag can be used to control a conditional jump or return instruction. These instructions
provide logical control following the manipulation of single bit, 8-bit byte, or 18-bit data
quantities.
A full set of logical operations, including AND, OR, XOR (exclusive-OR), CPL (NOR),
and NEG (two’s complement) are available for Boolean operations between the Accumu-
lator and all other 8-bit registers, memory locations, or immediate operands.
In addition, a full set of arithmetic and logical shifts in both directions are available which
operate on the contents of all 8-bit primary registers or directly on any memory location.
The carry flag can be included or set by these shift instructions to provide both the testing
of shift results and to link register/register or register/memory shift operations.
UM008011-0816 Specific Z80 Instruction Examples
Z80 CPU
User Manual
27
Specific Z80 Instruction Examples
Example 1
When a 737-byte data string in memory location DATA must be moved to location BUF-
FER, the operation is programmed as follows:
LD HL, DATA ;START ADDRESS OF DATA STRING
LD DE, BUFFER ;START ADDRESS OF TARGET BUFFER
LD BC, 737 ;LENGTH OF DATA STRING
LDIR ;MOVE STRING–TRANSFER MEMORY POINTED
;TO BY HL INTO MEMORY LOCATION POINTED
;TO BY DE INCREMENT HL AND DE,
;DECREMENT BC PROCESS UNTIL BC = 0
Eleven bytes are required for this operation and each byte of data is moved in 21 clock
cycles.
Example 2
A string in memory (limited to a maximum length of 132 characters) starting at location
DATA is to be moved to another memory location starting at location BUFFER until an
ASCII $ (used as a string delimiter) is found. This operation is performed as follows:
LD HL, DATA ;STARTING ADDRESS OF DATA STRING
LD DE, BUFFER ;STARTING ADDRESS OF TARGET BUFFER
LD BC, 132 ;MAXIMUM STRING LENGTH
LD A, '$' ;STRING DELIMITER CODE
LOOP: CP (HL) ;COMPARE MEMORY CONTENTS WITH
;DELIMITER
JR Z, END-$ ;GO TO END IF CHARACTERS EQUAL
LDI ;MOVE CHARACTER (HL) to (DE)
;INCREMENT HL AND DE, DECREMENT BC
JP PE, LOOP ;GO TO
LOOP IF MORE CHARACTERS
END: ;OTHERWISE, FALL THROUGH
;NOTE: P/V FLAG IS USED
;TO INDICATE THAT REGISTER BC WAS
;DECREMENTED TO ZERO
Nineteen bytes are required for this operation.
Example 3
A 16-digit decimal number is shifted as depicted in Figure 24. This shift is performed to
mechanize BCD multiplication or division. The 16-digit decimal number is represented in
packed BCD format (two BCD digits/byte) The operation is programmed as follows:
Hardware and Software Implementation UM008011-0816
28
Z80 CPU
User Manual
LD HL, DATA ;ADDRESS OF FIRST BYTE
LD B, COUNT ;SHIFT COUNT
XOR A ;CLEAR ACCUMULATOR
ROTAT: RLD ;ROTATE LEFT low-order DIGIT IN ACC
;WITH DIGITS IN (HL)
INC HL ;ADVANCE MEMORY POINTER.
DJNZ ROTAT-$ ;DECREMENT B AND GO TO ROTAT IF
;B IS NOT ZERO, OTHERWISE FALL
;THROUGH
Eleven bytes are required for this operation.
Example 4
One number is to be subtracted from another number, both of which exist in packed BCD
format and are of equal but varying length. The result is stored in the location of the minu-
end. The operation is programmed as follows:
LD HL, ARG1 ;ADDRESS OF MINUEND
LD DE, ARG2 ;ADDRESS OF SUBTRAHEND
LD B, LENGTH ;LENGTH OF TWO ARGUMENTS
AND A ;CLEAR CARRY FLAG
SUBDEC:LD A, (DE) ;SUBTRAHEND TO ACC
Figure 24. Shifting of BCD Digits/Bytes
0
UM008011-0816 Programming Task Examples
Z80 CPU
User Manual
29
SBC A, (HL) ;SUBTRACT (HL) FROM ACC
DAA ;ADJUST RESULT TO DECIMAL CODED VALUE
LD (HL), A ;STORE RESULT
INC HL ;ADVANCE MEMORY POINTERS
INC DE
DJNZ SUBDEC–$ ;DECREMENT B AND GO TO SUBDEC
;IF B
;NOT ZERO, OTHERWISE FALL
;THROUGH
Seventeen bytes are required for this operation.
Programming Task Examples
As indicated in Table 2, this example program sorts an array of numbers to ascending
order, using a standard exchange sorting algorithm. These numbers range from 0 to 255.
Table 2. Bubble Listing
Location
Object
Code Statement Source Statement
1 ; standard exchange (bubble) sort routine
2;
3 ; at entry: hl contains address of data
c contains number of elements to be sorted
(1 < c < 256)
4
5
6;
7 ; at exit data sorted in ascending order
8;
9 ; use of
registers
10 ;
11 ; register contents
12 ;
13 ; a temporary storage for calculations
14 ; b counter for data array
15 ; c length of data array
16 ; d first element in comparison
17 ; e second element in comparison
18 ; h flag to indicate exchange
Hardware and Software Implementation UM008011-0816
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Z80 CPU
User Manual
19 ; l unused
20 ; ix pointer into data array
21 ; iy unused
22 ;
0000 222600 23 sort: ld (data), hl ; save data address
0003 cb84 24 loop: res flag, h ; initialize exchange flag
0005 41 25 ld b, c ; initialize length counter
0006 05 26 dec b ; adjust for testing
0007 dd2a260
0
27 ld ix, (data) ; initialize array pointer
000b dd7e00 28 next: ld a, (ix) ; first element in comparison
000e 57 29 ld d, a ; temporary storage for element
goof dd5e01 30 ld e, (ix+1) ; second element in comparison
0012 93 31 sub e ; comparison first to second
0013 3008 32 jr pc, noex–$ ; if first > second, no jump
0015 dd7300 33 ld (ix), e ; exchange array elements
0018 dd7201 34 ld (ix+i), d
001b cbc4 35 set flag, h ; record exchange occurred
0010 dd23 36 noex: inc ix ; point to next data element
001f 10ea 37 djnz next–$ ; count number of comparisons
38 ; repeat if more data pairs
0021 cb44 39 bit flag, h ; determine if exchange occurred
0023 20de 40 jr nz, loop–$ ; continue if data unsorted
0025 c9 41 ret ; otherwise, exit
42 ;
0026 43 flag: equ 0 ; designation of flag bit
0026 44 data: defs 2 ; storage for data address
45 end
Table 2. Bubble Listing (Continued)
Location
Object
Code Statement Source Statement
UM008011-0816 Programming Task Examples
Z80 CPU
User Manual
31
The program outlined in Table 3 multiplies two unsigned 16-bit integers, leaving the result
in the HL register pair.
Table 3. Multiply Listing
Location
Object
Code Statement Source Statement
0000 1 mult:; unsigned sixteen bit integer multiply.
2 ; on entrance: multiplier in de.
3 ; multiplicand in hl.
4;
5 ; on exit result in hl.
6;
7 ; register uses:
8;
9;
10 ; h high-order partial result
11 ; l low-order partial result
12 ; d high-order multiplicand
13 ; e low-order multiplicand
14 ; b counter for number of shifts
15 ; c high-order bits of multiplier
16 ; a low-order bits of multiplier
17 ;
0000 0610 18 ld b, 16; number of bits-initialize
0002 4a 19 ld c, d; move multiplier
0003 7b 20 ld a, e;
0004 eb 21 ex de, hl; move multiplicand
0005 210000 22 ld hl, 0; clear partial result
0008 cb39 23 mloop: srl c; shift multiplier right
000a if 24 rra least-significant bit is
25 ; in carry.
000b 3001 26 jr nc,
noadd–$;
if no carry, skip the add.
good 19 27 add hl, de; else add multiplicand to
28 ; partial result.
000e eb 29 noadd: ex de, h l; shift multiplicand left
goof 29 30 add hl, hl; by multiplying it by two.
0010 eb 31 ex de, hl;
0011 10f5 32 djnz mloop–$; repeat until no more bits.
0013 c9 33 ret;
34 end;
Z80 CPU Instructions UM008011-0816
32
Z80 CPU
User Manual
Z80 CPU Instructions
The Z80 CPU can execute 158 different instruction types including all 78 of the 8080A
CPU. The instructions fall into these major groups:
• Load and Exchange
• Block Transfer and Search
• Arithmetic and Logical
• Rotate and Shift
• Bit Manipulation (Set, Reset, Test)
• Jump, Call, and Return
• Input/Output
• Basic CPU Control
Instruction Types
The load instructions move data internally among CPU registers or between CPU registers
and external memory. All of these instructions specify a source location from which the
data is to be moved, and a destination location. The source location is not altered by a load
instruction. Examples of load group instructions include moves between any of the gen-
eral-purpose registers such as move the data to Register B from Register C. This group
also includes load-immediate to any CPU register or to any external memory location.
Other types of load instructions allow transfer between CPU registers and memory loca-
tions. The exchange instructions can trade the contents of two registers.
A unique set of block transfer instructions is provided in the Z80 CPU. With a single
instruction, a block of memory of any size can be moved to any other location in memory.
This set of block moves is extremely valuable when processing large strings of data. With
a single instruction, a block of external memory of any required length can be searched for
any 8-bit character. When the character is found or the end of the block is reached, the
instruction automatically terminates. Both the block transfer and the block search instruc-
tions can be interrupted during their execution so they are not occupying the CPU for long
periods of time.
The arithmetic and logical instructions operate on data stored in the Accumulator and
other general-purpose CPU registers or external memory locations. The results of the
operations are placed in the Accumulator and the appropriate flags are set according to the
result of the operation.
UM008011-0816 Instruction Types
Z80 CPU
User Manual
33
An example of an arithmetic operation is adding the Accumulator to the contents of an
external memory location. The results of the addition are placed in the Accumulator. This
group also includes 16-bit addition and subtraction between 16-bit CPU registers.
The rotate and shift group allows any register or any memory location to be rotated right
or left, with or without carry, and either arithmetic or logical. Additionally, a digit in the
Accumulator can be rotated right or left with two digits in any memory location.
The bit manipulation instructions allow any bit in the Accumulator, any general-purpose
register, or any external memory location to be set, reset, or tested with a single instruc-
tion. For example, the most-significant bit of Register H can be reset. This group is espe-
cially useful in control applications and for controlling software flags in general-purpose
programming.
The JUMP, CALL, and RETURN instructions are used to transfer between multiple loca-
tions in the user’s program. This group uses several different techniques for obtaining the
new program counter address from specific external memory locations. A unique type of
call is the RESTART instruction. This instruction actually contains the new address as a
part of the 8-bit op code. This instruction is possible because only eight separate addresses
located in Page 0 of external memory can be specified. Program jumps can also be
achieved by loading Register HL, IX, or IY directly into the Program Counter, which
allows the jump address to be a complex function of the routine being executed.
The input/output group of instructions in the Z80 CPU allow for a wide range of transfers
between external memory locations or the general-purpose CPU registers, and the external
I/O devices. In each case, the port number is provided on the lower eight bits of the
address bus during any I/O transaction. One instruction allows this port number to be
specified by the second byte of the instruction while other Z80 instructions allow it to be
specified as the contents of the C Register. One major advantage of using the C register as
a pointer to the I/O device is that it allows multiple I/O ports to share common software
driver routines. This advantage is not possible when the address is part of the op code if
the routines are stored in ROM. Another feature of these input instructions is the auto-
matic setting of the Flag Register, making additional operations unnecessary to determine
the state of the input data. The parity state is one example.
The Z80 CPU includes single instructions that can move blocks of data (up to 256 bytes)
automatically to or from any I/O port directly to any memory location. In conjunction with
the dual set of general-purpose registers, these instructions provide fast I/O block transfer
rates. The power of this I/O instruction set is demonstrated by the Z80 CPU providing all
required floppy disk formatting on double-density floppy disk drives on an interrupt-
driven basis. For example, the CPU provides the preamble, address, data, and enables the
CRC codes.
Finally, the basic CPU control instructions allow multiple options and modes. This group
includes instructions such as setting or resetting the interrupt enable flip-flop or setting the
mode of interrupt response.
Z80 CPU Instructions UM008011-0816
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Z80 CPU
User Manual
Addressing Modes
Most of the Z80 instructions operate on data stored in internal CPU registers, external
memory, or in the I/O ports. Addressing refers to how the address of this data is generated
in each instruction. This section is a brief summary of the types of addressing used in the
Z80 CPU while subsequent sections detail the type of addressing available for each
instruction group.
Immediate Addressing
In the Immediate Addressing Mode, the byte following the op code in memory contains
the actual operand, as shown in Figure 25.
An example of this type of instruction is to load the Accumulator with a constant, in which
the constant is the byte immediately following the op code.
Immediate Extended Addressing
This mode is an extension of immediate addressing in that the two bytes following the op
codes are the operand, as shown in Figure 26.
An example of this type of instruction is to load the HL register pair (16-bit register) with
16 bits (two bytes) of data.
Figure 25. Immediate Addressing Mode
Figure 26. Immediate Extended Addressing Mode
One or Two Bytes
D7
D0
Op Code
Op Code
One or Two Bytes
low-order
high-order
Op Code
Op Code
Op Code
UM008011-0816 Modified Page Zero Addressing
Z80 CPU
User Manual
35
Modified Page Zero Addressing
The Z80 contains a special single-byte CALL instruction to any of eight locations in Page
0 of memory. This instruction, which is referred to as a restart, sets the Program Counter to
an effective address in Page 0. The value of this instruction is that it allows a single byte to
specify a complete 16-bit address at which commonly-called subroutines are located,
thereby saving memory space.
Relative Addressing
Relative addressing uses one byte of data following the op code to specify a displacement
from the existing program to which a program jump can occur. This displacement is a
signed two’s complement number that is added to the address of the op code of the follow-
ing instruction.
The value of relative addressing is that it allows jumps to nearby locations while only
requiring two bytes of memory space. For most programs, relative jumps are by far the
most prevalent type of jump due to the proximity of related program segments. Therefore,
these instructions can significantly reduce memory space requirements. The signed dis-
placement can range between +127 and –128 from A+2. This range allows for a total dis-
placement of +129 to –126 from the jump relative op code address. Another major
advantage is that it allows for relocatable code.
Figure 27. Modified Page Zero Addressing Mode
Figure 28. Relative Addressing Mode
One Byte
B7
B0
Op Code
Effective Address is
(B5 B4 B3 000)2
Op Code
Op Code
Jump Relative (One Byte Op Code)
8-bit Two’s Complement
Displacement Added to
Address (A+2)
Z80 CPU Instructions UM008011-0816
36
Z80 CPU
User Manual
Extended Addressing
Extended Addressing provides for two bytes (16 bits) of address to be included in the
instruction. This data can be an address to which a program can jump or it can be an
address at which an operand is located.
Extended addressing is required for a program to jump from any location in memory to
any other location, or load and store data in any memory location.
During extended addressing use, specify the source or destination address of an operand.
This notation (nn) is used to indicate the contents of memory at nn, in which nn is the 16-
bit address specified in the instruction. The two bytes of address nn are used as a pointer to
a memory location. The parentheses always indicates that the value enclosed within them
is used as a pointer to a memory location. For example, (1200) refers to the contents of
memory at location 1200.
Indexed Addressing
In the Indexed Addressing Mode, the byte of data following the op code contains a dis-
placement that is added to one of the two index registers (the op code specifies which
index register is used) to form a pointer to memory. The contents of the index register are
not altered by this operation.
An example of an indexed instruction is to load the contents of the memory location
(Index Register + Displacement) into the Accumulator. The displacement is a signed two’s
Figure 29. Extended Addressing Mode
Figure 30. Indexed Addressing Mode
Op Code
One or
Two Bytes
low-order Address to low-order Operand
high-order Address to low-order Operand
Op Code
Op Code
Displacement
Two-Byte Op Code
Operand added to index register
to form a pointer to memory
UM008011-0816 Register Addressing
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complement number. Indexed addressing greatly simplifies programs using tables of data
because the index register can point to the start of any table. Two index registers are pro-
vided because often operations require two or more tables. Indexed addressing also allows
for relocatable code.
The two index registers in the Z80 CPU are referred to as IX and IY. To indicate indexed
addressing, use the following notation:
(IX+d) or (IY+d)
In this notation, d is the displacement specified after the op code. The parentheses indicate
that this value is used as a pointer to external memory.
Register Addressing
Many of the Z80 op codes contain bits of information that specify which CPU register is to
be used for an operation. An example of register addressing is to load the data in Register
6 into Register C.
Implied Addressing
Implied addressing refers to operations in which the op code automatically implies one or
more CPU registers as containing the operands. An example is the set of arithmetic opera-
tions in which the Accumulator is always implied to be the destination of the results.
Register Indirect Addressing
This type of addressing specifies a 16-bit CPU register pair (such as HL) to be used as a
pointer to any location in memory. This type of instruction is powerful and it is used in a
wide range of applications.
An example of this type of instruction is to load the Accumulator with the data in the
memory location pointed to by the HL register contents. Indexed addressing is actually a
form of Register Indirect addressing except that a displacement is added with indexed
addressing. Register indirect addressing allows for powerful but simple to implement
memory accesses. The block move and search commands in the Z80 CPU are extensions
of this type of addressing in which automatic register incrementing, decrementing, and
comparing is added. The notation for indicating Register Indirect addressing is to put
Figure 31. Register Indirect Addressing Mode
Op Code
One or Two Bytes
Z80 CPU Instructions UM008011-0816
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User Manual
parentheses around the name of the register that is to be used as the pointer. For example,
the symbol (HL) specifies that the contents of the HL register are to be used as a pointer to
a memory location. Often Register Indirect addressing is used to specify 16-bit operands.
In this case, the register contents point to the lower order portion of the operand while the
register contents are automatically incremented to obtain the upper portion of the operand.
Bit Addressing
The Z80 contains a large number of bit set, reset, and test instructions. These instructions
allow any memory location or CPU register to be specified for a bit operation through one
of three previous addressing modes (register, Register Indirect, and indexed) while three
bits in the op code specify which of the eight bits is to be manipulated.
Addressing Mode Combinations
Many instructions include more than one operand (such as arithmetic instructions or
loads). In these cases, two types of addressing can be employed. For example, load can use
immediate addressing to specify the source and Register Indirect or indexed addressing to
specify the destination.
UM008011-0816 Instruction Notation Summary
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Instruction Notation Summary
Table 4 lists the operand notations and descriptions used in the Z80 Instruction Set.
Table 4. Instruction Notation Summary
Notation Description
r Identifies any of the registers A, B, C, D, E, H, or L
(HL)
Identifies the contents of the memory location, whose address is specified by
the contents of the register pair HL
(IX+d)
Identifies the contents of the memory location, whose address is specified by
the contents of the
Index register pair IX plus the signed displacement d
(IY+d)
Identifies the contents of the memory location, whose address is specified by
the contents of the
Index register pair IY plus the signed displacement d
n Identifies a one-byte unsigned integer expression in the range (0 to 255)
nn
Identifies a two-byte unsigned integer expression in the range
(0 to 65535)
d
Identifies a one-byte signed integer expression in the range
(
-128 to +127)
b
Identifies a one-bit expression in the range (0 to 7). The most-significant bit
to the left is bit 7 and the least-significant bit to the right is bit 0
e
Identifies a one-byte signed integer expression in the range
(-126 to +129) for
relative jump offset from current location
cc
Identifies the status of the
Flag Register as any of (NZ, Z, NC, C, PO, PE, P,
or M) for the conditional jumps, calls, and return instructions
qq Identifies any of the register pairs BC, DE, HL or AF
ss Identifies any of the register pairs BC, DE, HL or SP
pp Identifies any of the register pairs BC, DE, IX or SP
rr Identifies any of the register pairs BC, DE, IY or SP
s Identifies any of r, n, (HL), (IX+d) or (IY+d)
m Identifies any of r, (HL), (IX+d) or (IY+d)
Z80 CPU Instructions UM008011-0816
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User Manual
Instruction Op Codes
This section describes each of the Z80 instructions and provides tables listing the op codes
for every instruction. In each of these tables, the op codes in shaded areas are identical to
those offered in the 8080A CPU. Also depicted is the assembly language mnemonic that is
used for each instruction. All instruction op codes are listed in hexadecimal notation. Sin-
gle-byte op codes require two hex characters while double byte op codes require four hex
characters. For convenience, the conversion from hex to binary is repeated in Table 5.
The Z80 instruction mnemonics consist of an op code and zero, one, or two operands.
Instructions in which the operand is implied contains no operand. Instructions that contain
only one logical operand, in which one operand is invariant (such as the Logical OR
instruction), are represented by a one-operand mnemonic. Instructions that contain two
varying operands are represented by two operand mnemonics.
Table 5. Hex, Binary, Decimal Conversion Table
Hex Binary Decimal
0 = 0000 = 0
1 = 0001 = 1
2 = 0010 = 2
3=0011=3
4 = 0100 = 4
5 = 0101 = 5
6=0110=6
7 = 0111 = 7
8 = 1000 = 8
9 = 1001 = 9
A = 1010 = 10
B=1011=11
C=1100=12
D=1101=13
E=1110=14
F = 1111 = 15
UM008011-0816 Load and Exchange
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Load and Exchange
Table 6 defines the op codes for all of the 8-bit load instructions implemented in the Z80
CPU. Also described in this table is the type of addressing used for each instruction. The
source of the data is found on the top horizontal row and the destination is specified in the
left column. For example, load Register C from Register B uses the op code
48h. In all of
the figures, the op code is specified in hexadecimal notation and the
48h (0100 1000
binary) code is fetched by the CPU from external memory during M1 time, decoded, and
then the register transfer is automatically performed by the CPU.
The assembly language mnemonic for this entire group is LD, followed by the destination,
followed by the source (LD DEST, SOURCE).
Several combinations of addressing modes are possible. For example, the source can use
register addressing and the destination can be registered indirect; such as load the memory
location pointed to by Register HL with the contents of the D Register. The op code for this
operation is 72. The mnemonic for this load instruction is LD (HL), D.
Note:
Z80 CPU Instructions UM008011-0816
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User Manual
Table 6. 8-Bit Load Group LD
Source
Implied Register Reg Indirect Indexed Ext. Imm.
Destination I R A B C D E F L (HL) (BC) (DE) (IX+d) (lY+d) (nn) n
Register
A
ED
57
ED
5F
7F 78 79 7A 7B 7C 7D 7E 0A 1A
DD
7E
d
FD
7E
d
3A
nn
3E
n
B 47404142434445 46
DD
46
d
FD
46
d
06
n
C4F48494A4B4C4D4E
DD
4E
d
FD
4E
d
0E
n
D 5750515253545556
DD
56
d
FD
56
d
16
n
E5F58595A5B5C5D5E
DD
5E
d
FD
5E
d
1E
n
H 6760616263646566
DD
66
d
FD
66
d
26
n
L6F68696A6B6C6D6E
DD
6E
d
FD
6E
d
2E
n
Register
Indirect
(HL) 77 70 71 72 73 74 75
36
n
(BC) 02
(DE) 12
Indexed
(IX+d)
DD
77
d
DD
70
d
DD
71
d
DD
72
d
DD
73
d
DD
74
d
DD
75
d
DD
36
d
n
(IY+d)
FD
77
d
FD
70
d
FD
71
d
FD
72
d
FD
73
d
FD
74
d
FD
75
d
FD
36
d
n
Ext. Addr.
(nn)
32
n
n
.
Implied
I
ED
47
R
ED
4F
UM008011-0816 Load and Exchange
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Descriptions of the 8-Bit Load Group instructions begin on page 70.
The parentheses around the HL indicate that the contents of HL are used as a pointer to a
memory location. In all Z80 load instruction mnemonics, the destination is always listed
first, with the source following. The Z80 assembly language is defined for ease of pro-
gramming. Every instruction is self documenting and programs written in Z80 language
are easy to maintain.
In Table 6, some op codes that are available in the Z80 CPU use two bytes. This feature is
an efficient method of memory utilization because 8-, 18-, 24-, or 32-bit instructions are
implemented in the Z80 CPU. Often utilized instructions such as arithmetic or logical
operations are only eight bits, which results in better memory utilization than is achieved
with fixed instruction sizes such as 16 bits.
All load instructions using indexed addressing for either the source or destination location
actually use three bytes of memory, with the third byte being the displacement, d. For
example, a Load Register E instruction with the operand pointed to by IX with an offset of
+8 is written as:
LID E, (IX + 8)
The instruction sequence for this value in memory is shown in Figure 32.
The two extended addressing instructions are also three-byte instructions. For example,
the instruction to load the Accumulator with the operand in memory location
6F32h is
written as:
LID A, (6F 32h)
The instruction sequence for this value in memory is shown in Figure 33.
Figure 32. Example of a 3-Byte Load Indexed Instruction Sequence
Note:
Op Code
Address A
A+1
A+2
DD
5E
08
Displacement
Operand
Z80 CPU Instructions UM008011-0816
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User Manual
In this figure, note that the low-order portion of the address is always the first operand.
The load immediate instructions for the general-purpose 8-bit registers are two-byte
instructions. The instruction for loading Register H with the value
36h is written as:
LD H, 36h
The instruction sequence for this value in memory is shown in Figure 34.
Loading a memory location using indexed addressing for the destination and immediate
addressing for the source requires four bytes. For example:
LD (IX–15), 21h
The instruction sequence for this value in memory is shown in Figure 35.
Figure 33. Example of a 3-Byte Load Extended Instruction Sequence
Figure 34. Example of a 2-Byte Load Immediate Instruction Sequence
Figure 35. Example of a 4-Byte Load Indexed/Immediate Instruction Sequence
Op Code
Address A
A+1
A+2
3A
32
6F
low-order Address
high-order Address
Op Code
Address A
A+1
Operand
26
36
Op Code
One or Two Bytes
Address A
A+1
A+2
A+3
DD
36
F1
21
Displacement (–15 in Signed
Two’s Complement
Operand to Load
UM008011-0816 Load and Exchange
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In this figure, note that with any indexed addressing, the displacement always follows
directly after the op code.
Table 7 specifies the 16-bit load operations, for which the extended addressing feature
covers all register pairs. Register indirect operations specifying the stack pointer are the
PUSH and POP instructions. The mnemonic for these instructions is PUSH and POP.
Table 7. 16-Bit Load Group LD, PUSH, and POP
Source
Register Imm. Ext. Ext. Reg. Indir.
Register AF BC DE HL SP IX IY nn (nn) (SP)
AF P1
BC
01
n
n
ED
4B
n
n
C1
DE
11
n
n
ED
5B
n
n
D1
HL
21
n
n
2A
n
n
E1
SP F9
DD
F9
FD
F9
31
n
n
ED
7B
n
n
IX
DD
21
n
n
DD
2A
n
n
DD
E1
IY
FD
21
n
n
FD
2A
n
n
FD
E1
Extended
(nn)
ED
43
n
n
ED
53
n
n
22
n
n
ED
73
n
n
DD
22
n
n
FD
22
n
n
PUSH
Instructions →
Register
Indirect
(SP) F6 C6 D6 E6
DD
E6
FD
E6
. POP
Instructions
Note: The PUSH and POP instruction adjust the SP after every execution.
Z80 CPU Instructions UM008011-0816
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User Manual
Descriptions of the 16-Bit Load Group instructions begin on page 98.
These 16-bit load operations differ from other 16-bit loads in that the stack pointer is auto-
matically decremented and incremented as each byte is pushed onto or popped from the
stack, respectively. For example, the PUSH AF instruction is a single-byte instruction with
the op code of
F5h. During execution, this sequence is generated as:
Decrement SP
LD (SP), A
Decrement SP
LD (SP), F
The external stack now appears as shown in Figure 36.
The POP instruction is the exact reverse of a PUSH. All PUSH and POP instructions uti-
lize a 16-bit operand and the high-order byte is always pushed first and popped last.
PUSH BC is PUSH B then C
PUSH DE is PUSH D then E
PUSH HL is PUSH H then L
POP HL is POP L then H
The instruction using extended immediate addressing for the source requires two bytes of
data following the op code, as shown in the following example:
LD DE, 0659h
The instruction sequence for this value in memory is shown in Figure 37.
Figure 36. Example of a 16-Bit Load Operation
Note:
(SP)
(SP+1)
F
A
Top of stack
•
•
•
•
UM008011-0816 Block Transfer and Search
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In all extended immediate or extended addressing modes, the low-order byte always
appears first after the op code.
Table 8 lists the 16-bit exchange instructions implemented in the Z80 CPU. Op code
08h
allows the programmer to switch between the two pairs of Accumulator flag registers,
while
D9h allows the programmer to switch between the duplicate set of six general-pur-
pose registers. These op codes are only one byte in length to minimize the time necessary
to perform the exchange so that the duplicate banks can be used to make fast interrupt
response times.
Block Transfer and Search
Table 9 lists the extremely powerful block transfer instructions. These instructions operate
with three registers.
• HL points to the source location
• DE points to the destination location
• BC is a byte counter
Figure 37. Example of a 2-Byte Load Indexed/Immediate Instruction Sequence
Table 8. Exchanges EX and EXX
Implied Addressing
AF'
BC', DE',
and HL' HL IX IY
Implied
AF 08
BC
DE D9
HL
DE EB
Register
Indirect
(SP) E3
DD
E3
FD
E3
Address A
A+1
E6
07
Op Code
Operand
Z80 CPU Instructions UM008011-0816
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User Manual
After the programmer initializes these three registers, any of these four instructions can be
used. The Load and Increment (LDI) instruction moves one byte from the location pointed
to by HL to the location pointed to by DE. Register pairs HL and DE are then automati-
cally incremented and are ready to point to the following locations. The byte counter (i.e.,
register pair BC) is also decremented at this time. This instruction is valuable when the
blocks of data must be moved but other types of processing are required between each
move. The Load, Increment and Repeat (LDIR) instruction is an extension of the LDI
instruction. The same load and increment operation is repeated until the byte counter
reaches the count of zero. As a result, this single instruction can move any block of data
from one location to any other.
Because 16-bit registers are used, the size of the block can be up to 64 KB long
(1KB = 1024 bits) and can be moved from any location in memory to any other location.
Furthermore, the blocks can be overlapping because there are no constraints on the data
used in the three register pairs.
The LDD and LDDR instructions are similar to LDI and LDIR. The only difference is that
register pairs HL and DE are decremented after every move so that a block transfer starts
from the highest address of the designated block rather than the lowest.
Table 10 specifies the op codes for the four block search instructions. The first, CPI (Com-
pare and Increment) compares the data in the Accumulator with the contents of the mem-
ory location pointed to by Register HL. The result of the compare is stored in one of the
flag bits and the HL register pair is then incremented and the byte counter (register pair
BC) is decremented.
Table 9. Block Transfer Group
Destination Source
Register
Indirect
(DE) Register
Indirect
(HL)
(ED)
A0
LDI – Load (DE) → (HL)
Inc HL and DE, Dec BC
(ED)
B0
LDIR, – Load (DE) → (HL)
Inc HL and DE, Dec BC; repeat until BC = 0.
(ED)
A8
LDD – Load (DE) → (HL)
Inc HL and DE, Dec BC
(ED)
B8
LDDR – Load (DE) → (HL)
Dec HL and DE, Dec BC; repeat until BC = 0.
Note: Register HL points to the source; the DE Register points to the destination; the BC Register is a byte counter.
UM008011-0816 Arithmetic and Logical
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Descriptions of the Exchange, Block Transfer, and Search Group instructions begin on
page 123.
The CPIR instruction is merely an extension of the CPl instruction in which the compare is
repeated until either a match is found or the byte counter (register pair BC) becomes zero.
As a result, this single instruction can search the entire memory for any 8-bit character.
The Compare and Decrement (CPD) and Compare, Decrement, and Repeat (CPDR)
instructions are similar; however, their only difference is that they decrement HL after
every compare so that they search the memory in the opposite direction; i.e., the search is
started at the highest location in the memory block.
These block transfer and compare instructions are extremely powerful in string manipula-
tion applications.
Arithmetic and Logical
Table 11 lists all of the 8-bit arithmetic operations that can be performed with the Accu-
mulator. Also listed are the increment (INC) and decrement (DEC) instructions. In all of
these instructions, with the exception of INC and DEC, the specified 8-bit operation is per-
formed between the data in the Accumulator and the source data.
Table 10. Block Search Group
Search Location
Register Indirect
(HL)
(ED)
A1
CPI
Inc HL, Dec BC
(ED)
B1
CPRI. Inc HL, Dec BC
Repeat until) BC = 0 or find match
(ED)
A9
WD Dec HL and BC
(ED)
B9
CPDR Dec HL and BC
Repeat until BC = 0 or find match
Note: HL points to a location in memory to be compared with
Accumulator contents; BC is a byte counter.
Note:
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User Manual
Descriptions of the 8-Bit Arithmetic Group instructions begin on page 144.
The result of the operation is placed in the Accumulator with the exception of the compare
(CP) instruction, which leaves the Accumulator unchanged. All of these operations effect
the Flag Register as a result of a specified operation.
Table 11. 8-Bit Arithmetic and Logic
Source
Register Addressing
Register
Indirect Indexed Immediate
Destination A B C D E F L (HL) (IX+d) (lY+d) n
ADD 87808182838485 88
DD
86
d
FD
86
d
C6
n
Add with Carry
ADC
8F 88 89 8A 8B 8C 8D 8E
DD
8E
d
FD
8E
d
CE
n
Subtract
SUB
97 90 91 92 93 94 95 96
DD
96
d
FD
96
d
D6
n
Subtract with Carry
SBC
9F 98 99 9A 9B 9C 9D 9E
DD
9E
d
FD
9E
d
DE
n
AND A7A0A1A2A3A4A5 A6
DD
A6
d
FD
A6
d
E6
n
XOR AF A8 A9 AA AB AC AD AE
DD
AE
d
FD
AE
d
EE
n
OR B7 B0 B1 B2 B3 B4 B5 B6
DD
B6
d
FD
B6
d
F6
n
Compare
CP
BF B8 B9 BA BB BC BD BE
DD
BE
d
FD
BE
d
FE
n
Increment
INC
3C 04 0C 14 1C 24 2C 34
DD
34
d
FD
34
d
Decrement
DEC
3D 05 0D 15 1D 25 2D 35
DD
35
d
FD
35
d
Note:
UM008011-0816 Arithmetic and Logical
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The INC and DEC instructions specify a register or a memory location as both the source
and the destination of the result. When the source operand is addressed using the index
registers, the displacement must directly follow. With immediate addressing, the actual
operand directly follows. As an example, the AND
07h instruction is shown in Figure 38.
Assuming that the Accumulator contains the value
F3h, the result of 03h is placed in the
Accumulator:
The Add (ADD) instruction performs a binary add between the data in the source location
and the data in the Accumulator. The Subtract (SUB) instruction performs a binary sub-
traction. When an Add with Carry (ADC) or Subtract with Carry (SBC) instruction is
specified, the Carry flag is also added or subtracted, respectively. The flags and the Deci-
mal Adjust (DAA) instruction in the Z80 CPU allow arithmetic operations for processing
the following items:
• Multiprecision packed BCD numbers
• Multiprecision signed or unsigned binary numbers
• Multiprecision two’s complement signed numbers
Other instructions in this group are the Logical And (AND), Logical Or (OR), Exclusive
Or (XOR), and Compare (CP) instructions.
Five general-purpose arithmetic instructions operate on the Accumulator or Carry flag.
These five instructions are listed in Table 12.
Figure 38. Example of an AND Instruction Sequence
Accumulator before operation 1111 0011 = F3h
Operand 0000 0111 = 07h
Result to Accumulator 0000 0011 = 03h
Table 12. General-Purpose AF Operation
Decimal Adjust Accumulator (DAA) 27
Complement Accumulator (CPL) 2F
Negate Accumulator (NEG)
(two’s complement
ED
44
Complement Carry Flag (CCF) 3F
Set Carry Flag (SCF) 37
Address A
A+1
E6
07
Op Code
Operand
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Descriptions of the General-Purpose Arithmetic and CPU Control Groups instructions
begin on page 172.
The decimal adjust instruction can adjust for subtraction and addition, making BCD arith-
metic operations simple.
1. To allow for this operation, the N flag is used. This flag is set if the most recent arithmetic
operation was a Subtract. The Negate Accumulator (NEG) instruction forms the two’s
complement of the number in the Accumulator.
2. A Reset Carry instruction is not included in the Z80 CPU, because this operation can
be easily achieved through other instructions such as a logical AND of the Accumu-
lator with itself.
Table 12 lists all of the 16-bit arithmetic operations between 16-bit registers. There are
five groups of instructions, including the Add with Carry and Subtract with Carry instruc-
tions; ADC and SBC affect all of the flags. These two groups simplify address calculation
or other 16-bit arithmetic operations.
Descriptions of the 16-Bit Arithmetic Group instructions begin on page 187.
Table 13. 16-Bit Arithmetic
Source
BC DE HL SP IX IY
Destination HL 09 19 29 39
Add (ADD)
IX
DD
09
DD
19
DD
39
DD
29
IY
FD
09
FD
19
FD
39
FD
29
Add with Carry and set ADC flags HL
ED
4A
ED
5A
ED
6A
ED
7A
Subtract with Carry and set SBC flags HL
ED
42
ED
52
ED
62
ED
72
Increment (INC) 03 13 23 33
DD
23
FD
23
Decrement (DEC) DB 1B 2B 3B
DD
2B
FD
2B
Note:
Notes:
Note:
UM008011-0816 Rotate and Shift
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Rotate and Shift
A major feature of the Z80 CPU is to rotate or shift data in the Accumulator, any general-
purpose register, or any memory location. All of the Rotate and Shift op codes are
depicted in Figure 39. Also included in the Z80 CPU are arithmetic and logical shift oper-
ations. These operations are useful in a wide range of applications including integer multi-
plication and division. Two BCD digit rotate instructions (RRD and RLD) allow a digit in
the Accumulator to be rotated with the two digits in a memory location pointed to by reg-
ister pair HL. These instructions allow for efficient BCD arithmetic.
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Descriptions of the Rotate and Shift Group instructions begin on page 204.
Figure 39. Rotates and Shifts
Source
Type
of
Rotate
Shift
A B C D E F L (HL) (IX+d) (lY+d) A
RCL
CB
07
CB
00
CB
01
CB
02
CB
03
CB
04
CB
06
CB
0E
DD
CB
d
06
FD
CB
d
06
RLCA 07
RRC
CB
0F
CB
08
CB
09
CB
0A
CB
06
CB
0C
CB
0D
CB
0E
DD
CB
d
0E
FD
CB
d
0E
RRCA 0F
RL
CB
17
CB
10
CB
11
CB
12
CB
13
CB
14
CB
15
CB
16
DD
CB
d
16
FD
CB
d
16
RLA 17
RR
CB
1F
CB
18
CB
19
CB
1A
CB
1B
CB
1C
CB
1D
CB
1E
DD
CB
d
1E
FD
CB
d
1E
RRA 1F
SLA
CB
27
CB
20
CB
21
CB
22
CB
23
CB
24
CB
25
CB
26
DD
CB
d
26
FD
CB
d
26
SRA
CB
2F
CB
28
CB
29
CB
2A
CB
2B
CB
2C
CB
2D
CB
2E
DD
CB
d
2E
FD
CB
d
2E
SRL
CB
3F
CB
38
CB
39
CB
3A
CB
3B
CB
3C
CB
3D
CB
3E
DD
CB
d
3E
FD
CB
d
3E
ED
6F
ED
67
CY
CY
0
ACC
ACC
Rotate
Left Circular
Rotate
Right Circular
Rotate
Left
Rotate
Right
Shift
Left Arithmetic
Shift
Right Arithmetic
Shift
Right Logical
(HL)
(HL)
b
7
b
0
b
7
–b
4
b
3
–b
0
b
3
–b
0
Rotate
Digit
Right
Rotate
Digit
Left
Note:
UM008011-0816 Bit Manipulation
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55
Bit Manipulation
The ability to set, reset, and test individual bits in a register or memory location is required
in almost every program. These bits can be flags in a general-purpose software routine,
indications of external control conditions, or data packed into memory locations, making
memory utilization more efficient.
With a single instruction, the Z80 CPU can set, reset, or test any bit in the Accumulator, in
any general-purpose register, or in any memory location. Table 14 lists the 240 instruc-
tions that are available for this purpose.
Table 14. Bit Manipulation Group
Register Addressing
Register
Indirect Indexed
A 8 C D E H L (HL) (IX+d) (IY+d)
Bit DD FD
Test Bit
0
C8 C8 C8 C8 C8 C8 C8 C8 C8 C8
47 40 41 42 43 44 45 46 d d
1
46 46
DD FD
C8 C8 C8 C8 C8 C8 C8 C8 C8 C8
4F 48 49 4A 48 4C 4D 4E d d
4E 4E
2
DD FD
C8 C8 C8 C8 C8 C8 C8 C8 C8 C8
57 50 51 52 53 54 55 56 d d
56 56
3
DD FD
C8 C8 C8 C8 C8 C8 C8 C8 C8 C8
5F 58 59 5A 5B 5C 5D 5E d d
46 46
4
DD FD
C8 C8 C8 C8 C8 C8 C8 C8 C8 C8
67 60 61 62 63 64 65 66 d d
66 66
5
DD FD
C8 C8 C8 C8 C8 C8 C8 C8 C8 C8
6F 68 69 6A 68 6C 6D 6E d d
6E 6E
Z80 CPU Instructions UM008011-0816
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User Manual
Test Bit
(cont’d.)
6
DD FD
C8 C8 C8 C8 C8 C8 C8 C8 C8 C8
77 70 71 72 73 74 75 76 d d
76 76
7
DD DD
C8 C8 C8 C8 C8 C8 CS C8 C8 C8
7F 78 79 7A 78 7C 7D 7E d d
46 46
Rest Bit
RES
0
DD FD
C8 C8 C8 C8 C8 C8 C8 C8 C8 C8
87 80 81 82 83 84 85 86 d d
86 86
1
DD FD
C8 C8 C8 C8 C8 C8 C8 C8 C8 C8
8F 88 89 8A 88 8C 8D 8E d d
8E 8E
2
DD FD
C8 C8 CS C8 C8 C8 C8 C8 C8 C8
97 90 91 92 93 94 95 96 d d
96 96
3
DD FD
C8 C8 C8 C8 CS C8 C8 C8 C8 C8
9F 98 99 9A 98 90 90 9E d d
9E 9E
4
DD FD
C8 C8 C8 C8 C6 C8 C8 C8 C8 C8
A7 AO AI A2 A3 A4 A5 A6 d d
A6 A6
5
DD FD
C8 C8 C8 C8 08 C8 C8 C8 C8 C8
AF A8 A9 AA AB AC AD AE d d
AE AE
6
DD FD
C8 C8 C8 C8 C8 C8 C8 C8 C8 C8
B7 B0 B1 82 B3 B4 B5 B6 d d
B6 B6
Table 14. Bit Manipulation Group (Continued)
Register Addressing
Register
Indirect Indexed
UM008011-0816 Bit Manipulation
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57
Rest Bit
RES
(cont’d.) 7
DD DD
C8 C8 C8 C8 C8 C8 C8 C8 C8 C8
BF B8 89 8A B8 8C BD 9E d d
BE BE
Set Bit
SET
0
DD FD
C8 C8 C8 C8 C8 C8 C8 C8 C8 C8
C7 C0 C1 C2 C3 C4 C5 C6 d d
C6 C6
1
DD FD
C8 C8 C8 C8 C8 C8 C8 C8 C8 C8
CF C8 C9 CA C8 CC CD CE d d
CE CE
2
DD FD
C8 C8 C8 C8 C8 C8 C8 C8 C8 C8
D7 DO D1 D2 D3 D4 DS D6 d d
D6 D6
3
DD FD
C8 C8 C8 C8 C8 C8 C8 C8 C8 C8
DF D8 09 DA DS DC DD DE d d
DE DE
4
DD FD
C8 C8 C8 C8 C8 C8 C8 C8 C8 C8
E7 E0 E1 E2 E3 E4 E5 E6 d d
E6 E6
5
DD FD
C8 C8 C8 C8 C8 C8 C8 C8 C8 C8
EF E8 E9 EA EB EC ED EE d d
EE EE
6
DD FD
C8 C8 C8 C8 C8 C8 C8 C8 C8 C8
F7 FO F1 F2 F3 F4 FS F6 d d
F6 F6
7
DD FD
C8 C8 C8 C8 C8 C8 C8 C8 C8 C8
FF F8 F9 FA FB FC FD FE d d
FE FE
Table 14. Bit Manipulation Group (Continued)
Register Addressing
Register
Indirect Indexed
Z80 CPU Instructions UM008011-0816
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User Manual
Register addressing can specify the Accumulator or any general-purpose register on which
an operation is to be performed. Register Indirect and Indexed addressing are available for
operations at external memory locations. Bit test operations set the Zero flag (Z) if the
tested bit is a 0.
Descriptions of the Bit Set, Reset, and Test Group instructions begin on page 242.
Jump, Call, and Return
Table 15 lists all of the jump, call, and return instructions implemented in the Z80 CPU. A
jump is a branch in a program in which the program counter is loaded with a 16-bit value
as specified by one of the three available addressing modes (Immediate Extended, Rela-
tive, or Register Indirect). In Table 15, the jump group includes several conditions that can
be specified before the jump is made. If these conditions are not met, the program merely
continues with the next sequential instruction. The conditions are all dependent on the data
in the Flag Register. The immediate extended addressing is used to jump to any location in
the memory. This instruction requires three bytes (i.e., two bytes designated to specifying
the 16-bit address), with the low-order address byte first, followed by the high-order
address byte.
An example of an unconditional jump to memory location
3E32h is shown in Figure 40.
The Relative Jump instruction uses only two bytes, the second byte is a signed two’s com-
plement displacement from the existing Program Counter. This displacement can be in the
range of +129 to –126 and is measured from the address of the instruction op code.
Figure 40. Example of an Unconditional Jump Sequence
Note:
Op Code
Address A
A+1
A+2
C3
32
3E
low-order Address
high-order Address
UM008011-0816 Jump, Call, and Return
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User Manual
59
Descriptions of the Jump Group instructions begin on page 261.
Three types of Register Indirect jumps are also included. These instructions are imple-
mented by loading the register pair HL or one of the index registers IX or IY directly into
the Program Counter. This feature allows for program jumps to be a function of previous
calculations.
A Call is a special form of a jump in which the address of the byte following the call
instruction is pushed onto the stack before the jump is made. A return instruction is the
reverse of a call because the data on the top of the stack is popped directly into the Pro-
Table 15. Jump, Call, and Return Group
Condition
Un-
Cond. Carry
Non-
Carry Zero
Non-
Zero
Parity
Even
Parity
Odd
Sign
Neg
Sign
Pos
Reg
B¹0
JUMP
JP
IMMED.
EXT.
nn
C3
n
n
D8
n
n
D2
n
n
CA
n
n
C2
n
n
EA
n
n
E2
n
n
FA
n
n
F2
n
n
JUMP
JR
RELATIVE PC+e
18
e–2
38
e–2
30
e–2
28
e–2
20
e–2
JUMP
JP
Register
INDIR.
(HL) EB
(IX)
DD
E9
(IY)
FD
E9
CALL
IMMED.
EXT.
nn
CD
n
n
DC
n
n
D4
n
n
CC
n
n
C4
n
n
EC
n
n
E4
n
n
FC
n
n
F4
n
n
Decrement B,
Jump If Non-Zero
DJNZ
RELATIVE PC+e
10
e–2
Return
RE
REGISTER
INDIR.
(SP)
(SP+1)
C9 D8 D0 C8 C0 E8 E0 F8 F0
Return From
Interrupt
RETI
ED
4D
Return From Non-
Maskable
Interrupt
RETN
ED
45
Note:
Z80 CPU Instructions UM008011-0816
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User Manual
gram Counter to form a jump address. The call and return instructions allow for simple
subroutine and interrupt handling. Two special return instruction are included in the Z80
family of microprocessors. The return from interrupt instruction (RETI) and the return
from nonmaskable interrupt (RETN) are treated in the CPU as an unconditional return
identical to the op code C9h. The difference is that (RETI) can be used at the end of an
interrupt routine and all Z80 peripheral chips recognize the execution of this instruction
for proper control of nested priority interrupt handling. This instruction, coupled with the
Z80 CPU’s peripheral devices implementation, simplifies the normal return from nested
interrupt. Without this feature, the following software sequence is necessary to inform the
interrupting device that the interrupt routine is completed:
Disable Interrupt ; Prevent interrupt before routine is exited.
LD A, n ; Notify peripheral that service routine
; is complete.
OUT n, A
Enable Interrupt
Return
This seven-byte sequence can be replaced with the one-byte EI instruction and the two-
byte RETI instruction in the Z80 CPU. This instruction is important because interrupt ser-
vice time often must be minimized.
The DJNZ instruction is used to facilitate program loop control. This two-byte relative
jump instruction decrements Register B, and the jump occurs if Register B is not decre-
mented to 0. The relative displacement is expressed as a signed two’s complement num-
ber. A simple example of its use is shown in Table 16.
Table 17 lists the eight op codes for the Restart instruction, which is a single-byte call to
any of the eight addresses listed. A simple mnemonic for each of these eight calls is also
listed. The Restart instruction is useful for frequently-used routines due to its minimal
memory consumption.
Table 16. Example Usage of the DJNZ Instruction
Address Instruction Comments
N, N+1 LD B, 7 ; Set B Register to count of 7
N+2 to N+9 (Perform a sequence of instructions) ; Loop to be performed 7 times
N+10,N+11 DJNZ – 8 ; To jump from N+12 to N+2
N + 12 (Next instruction)
UM008011-0816 Input/Output
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61
Descriptions of the Call and Return Group instructions begin on page 280.
Input/Output
The Z80 CPU contains an extensive set of input and output instructions, as shown in
Tables 18 and 19. The addressing of the input or output device can be either absolute or
Register Indirect, using the C register. In the Register Indirect addressing mode, data can
be transferred between the I/O devices and any of the internal registers. In addition, eight
block transfer instructions are implemented. These instructions are similar to the memory
block transfers except that they use register pair HL for a pointer to the memory source
(output commands) or destination (input commands) while Register B is used as a byte
counter. Register C holds the address of the port for which the input or output command is
required. Because Register B is eight bits in length, the I/O block transfer command han-
dles up to 256 bytes.
In the IN A and OUT n, A instructions, the I/O device’s n address appears in the lower half
of the address bus (A7–A0), while the Accumulator content is transferred in the upper half
of the address bus. In all Register Indirect input output instructions, including block I/O
transfers, the contents of the C Register are transferred to the lower half of the address bus
(device address) while the contents of Register B are transferred to the upper half of the
address bus.
Table 17. Restart Group
Op Code
CALL Address
0000h C7 RST 0
0008h CF RST 8
0010h D7 RST 16
0018h DF RST 24
0020h E7 RST 32
0028h EF RST 40
0030h F7 RST 48
0038h FF RST 56
Note:
Z80 CPU Instructions UM008011-0816
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User Manual
Table 18. Input Group
Immediate
(n)
Register
Indirect)
(c)
Input
Destination
Input
IN
Register
Address
A
DB
n
ED
7B
B
ED
40
C
ED
48
D
ED
50
E
ED
58
H
ED
60
L
ED
68
INI: input &
inc HL, Dec B
Register
Indir
(HL)
ED
A2
Block
Input
Commands
INIR: INP, Inc HL,
Dec B, repeat if B≠0
ED
B2
IND: input & Inc
Dec HL, Dec B
ED
AA
INDR: input, Dec HL,
Dec B, repeat if B≠0
ED
BA
UM008011-0816 CPU Control Group
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63
Descriptions of the Input and Output Group instructions begin on page 294.
CPU Control Group
Table 20 shows the six general-purpose CPU control instructions. The HALT instruction
suspends CPU operation until a subsequent interrupt is received, while the DI and EI are
used to lock out and enable interrupts. The three interrupt mode commands set the CPU to
any of the three available interrupt response modes; each of these is described in the next
paragraph. The NOP instruction has no function.
Table 19. 8-Bit Arithmetic and Logic
Source
Register Register Indirect
AB CDE HL (HL)
11OUT
Immediate (n)
D3
n
Register
Indirect
(c)
ED
79
ED
41
ED
49
ED
51
ED
59
ED
61
ED
69
11OUT: output
inc HL, dec B
ED
A3
Block
Output
Command
11OUT: output
dec B, repeat if B≠0
ED
B3
11OUT: output
dec HL and B
ED
AB
11OUTDR: output, dec
HL and B, repeat if
B≠0
ED
BB
Port
Destination
Address
Note:
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User Manual
If Mode 0 is set, the interrupting device can insert any instruction on the data bus and
allow the CPU to execute it. Mode 1 is a simplified mode in which the CPU automatically
executes a restart (RST) at address
0038h so that no external hardware is required (the old
Program Counter content is pushed onto the stack). Mode 2 is the most powerful because
it allows for an indirect call to any location in memory. With this mode, the CPU forms a
16-bit memory address in which the upper eight bits are the contents of Register I, and the
lower eight bits are supplied by the interrupting device. This address points to the first of
two sequential bytes in a table in which the address of the service routine is located, as
shown in Figure 41. The CPU automatically obtains the starting address and performs a
CALL instruction to this address.
Table 20. Miscellaneous CPU Control
NOP 00
HALT 76
Disable INT (EI) F3
Enable INT (EI) FB
Set INT Mode 0
IM0
ED
46
8080A mode
Set INT Mode 1
IM1
ED
56
Call to address 0038h
Set INT Mode 2
IM2
ED
5E
Indirect call using Register I and B bits from
INTER device as a pointer
Figure 41. Mode 2 Interrupt Command
Pointer to Interrupt Table,
Address of Interrupt
Service Routine
Register I is Upper Address,
Peripheral Supplies
Lower Address
UM008011-0816 Z80 Instruction Set
Z80 CPU
User Manual
65
Z80 Instruction Set
This chapter provides a description of the assembly language instructions available with
the Z80 CPU.
Z80 Assembly Language
Assembly language allows the user to write a program without concern for memory
addresses or machine instruction formats. It uses symbolic addresses to identify memory
locations and mnemonic codes (op codes and operands) to represent the instructions.
Labels (symbols) are assigned to a particular instruction step in a source program to iden-
tify that step as an entry point for use in subsequent instructions. Operands following each
instruction represent storage locations, registers, or constant values. The assembly lan-
guage also includes assembler directives that supplement the machine instruction. A
pseudo-op, for example, is a statement that is not translated to a machine instruction, but
rather is interpreted as a directive that controls the assembly process.
A program written in assembly language is called a source program, which consists of
symbolic commands called statements. Each statement is written on a single line and can
consist of one to four entries: A label field, an operation field, an operand field, and a com-
ment field. The source program is processed by the assembler to obtain a machine lan-
guage program (object program) that can be executed directly by the Z80 CPU.
Zilog provides several assemblers that differ in the features offered. Both absolute and
relocatable assemblers are available with the Development and Micro-computer Systems.
The absolute assembler is contained in base level software operating in a 16K memory
space, while the relocating assembler is part of the RIO environment operating in a 32K
memory space.
Z80 Status Indicator Flags
The Flag registers, F and F', supply information to the user about the status of the Z80
CPU at any particular time. The bit positions for each flag are listed in Table 21 and
defined in
Table 21. Flag Register Bit Positions
Bit 76543210
Position SZXHXP/VNC
Z80 Instruction Set UM008011-0816
66
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Each of these two Flag registers contains 6 bits of status information that are set or cleared
by CPU operations; bits 3 and 5 are not used. Four of these bits (C, P/V, Z, and S) can be
tested for use with conditional JUMP, CALL, or RETURN instructions. The H and N flags
cannot be tested; these two flags are used for BCD arithmetic.
Carry Flag
The Carry Flag (C) is set or cleared depending on the operation being performed. For
ADD instructions that generate a Carry, and for SUB instructions that generate a Borrow,
the Carry Flag is set. The Carry Flag is reset by an ADD instruction that does not generate
a Carry, and by a SUB instruction that does not generate a Borrow. This saved Carry facil-
itates software routines for extended precision arithmetic. Additionally, the DAA instruc-
tion sets the Carry Flag if the conditions for making the decimal adjustment are met.
For the RLA, RRA, RLS, and RRS instructions, the Carry bit is used as a link between the
least-significant byte (LSB) and the most-significant byte (MSB) for any register or mem-
ory location. During the RLCA, RLC, and SLA instructions, the Carry flag contains the
final value shifted out of bit 7 of any register or memory location. During the RRCA,
RRC, SRA, and SRL instructions, the Carry flag contains the final value shifted out of bit
0 of any register or memory location.
For the logical instructions AND, OR, and XOR, the Carry flag is reset.
The Carry flag can also be set by the Set Carry Flag (SCF) instruction and complemented
by the Compliment Carry Flag (CCF) instruction.
Add/Subtract Flag
The Add/Subtract Flag (N) is used by the Decimal Adjust Accumulator instruction (DAA)
to distinguish between the ADD and SUB instructions. For ADD instructions, N is cleared
to 0. For SUB instructions, N is set to 1.
Table 22. Flag Definitions
Symbol Field Name
CCarry Flag
N Add/Subtract
P/V Parity/Overflow Flag
HHalf Carry Flag
Z Zero Flag
S Sign Flag
XNot Used
UM008011-0816 Decimal Adjust Accumulator Flag
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67
Decimal Adjust Accumulator Flag
The Decimal Adjust Accumulator (DAA) instruction uses this flag to distinguish between
ADD and SUBTRACT instructions. For all ADD instructions, N sets to 0. For all SUB-
TRACT instructions, N sets to 1.
Parity/Overflow Flag
The Parity/Overflow (P/V) Flag is set to a specific state depending on the operation being
performed. For arithmetic operations, this flag indicates an overflow condition when the
result in the Accumulator is greater than the maximum possible number (+127) or is less
than the minimum possible number (–128). This overflow condition is determined by
examining the sign bits of the operands.
For addition, operands with different signs never cause overflow. When adding operands
with similar signs and the result contains a different sign, the Overflow Flag is set, as
shown in the following example.
The two numbers added together result in a number that exceeds +127 and the two posi-
tive operands result in a negative number (–95), which is incorrect. The Overflow Flag is
therefore set.
For subtraction, overflow can occur for operands of unalike signs. Operands of alike signs
never cause overflow, as shown in the following example.
The minuend sign has changed from a positive to a negative, resulting in an incorrect dif-
ference; the Overflow Flag is set.
Another method for identifying an overflow is to observe the Carry to and out of the sign
bit. If there is a Carry in and no Carry out, or if there is no Carry in and a Carry out, then
an Overflow has occurred.
This flag is also used with logical operations and rotate instructions to indicate the result-
ing parity is even. The number of 1 bits in a byte are counted. If the total is Odd, ODD par-
ity is flagged (i.e., P = 0). If the total is even, even parity is flagged (i.e., P = 1).
+120 = 0111 1000 ADDEND
+105 = 0110 1001 AUGEND
+225 = 1110 0001 (–95) SUM
+127 0111 1111 MINUEND
(–) –64 1100 0000 SUBTRAHEND
+191 1011 1111 DIFFERENCE
Z80 Instruction Set UM008011-0816
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During the CPI, CPIR, CPD, and CPDR search instructions and the LDI, LDIR, LDD, and
LDDR block transfer instructions, the P/V Flag monitors the state of the Byte Count (BC)
Register. When decrementing, if the byte counter decrements to 0, the flag is cleared to 0;
otherwise the flag is set to1.
During the LD A, I and LD A, R instructions, the P/V Flag is set with the value of the inter-
rupt enable flip-flop (IFF2) for storage or testing.
When inputting a byte from an I/O device with an IN r, (C) instruction, the P/V Flag is
adjusted to indicate data parity.
Half Carry Flag
The Half Carry Flag (H) is set (1) or cleared (0) depending on the Carry and Borrow status
between bits 3 and 4 of an 8-bit arithmetic operation. This flag is used by the Decimal
Adjust Accumulator (DAA) instruction to correct the result of a packed BCD add or sub-
tract operation. The H Flag is set (1) or cleared (0) as shown in Table 23.
Zero Flag
The Zero Flag (Z) is set (1) or cleared (0) if the result generated by the execution of certain
instructions is 0.
For 8-bit arithmetic and logical operations, the Z flag is set to a 1 if the resulting byte in
the Accumulator is 0. If the byte is not 0, the Z flag is reset to 0.
For Compare (search) instructions, the Z flag is set to 1 if the value in the Accumulator is
equal to the value in the memory location indicated by the value of the register pair HL.
When testing a bit in a register or memory location, the Z flag contains the complemented
state of the indicated bit (see Bit b, r in the Bit Set, Reset, and Test Group
section on page
242).
When inputting or outputting a byte between a memory location and an INI, IND, OUTI,
or OUTD I/O device, if the result of decrementing Register B is 0, then the Z flag is 1; oth-
erwise, the Z flag is 0. Additionally, for byte inputs from I/O devices using IN r, (C), the Z
flag is set to indicate a 0-byte input.
Table 23. Half Carry Flag Add/Subtract Operations
H Flag Add Subtract
1 A Carry occurs from bit 3 to bit 4 A Borrow from bit 4 occurs
0 No Carry occurs from bit 3 to bit 4 No Borrow from bit 4 occurs
UM008011-0816 Sign Flag
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69
Sign Flag
The Sign Flag (S) stores the state of the most-significant bit of the Accumulator (bit 7).
When the Z80 CPU performs arithmetic operations on signed numbers, the binary twos-
complement notation is used to represent and process numeric information. A positive
number is identified by a 0 in Bit 7. A negative number is identified by a 1. The binary
equivalent of the magnitude of a positive number is stored in bits 0 to 6 for a total range of
from 0 to 127. A negative number is represented by the twos complement of the equiva-
lent positive number. The total range for negative numbers is from –1 to –128.
When inputting a byte from an I/O device to a register using an IN r, (C) instruction, the S
Flag indicates either positive (S = 0) or negative (S = 1) data.
Z80 Instruction Description
Execution time (E.T.) for each instruction is provided in microseconds for an assumed
4 MHz clock. Total machine cycles (M) are indicated with total clock periods, or T states.
Also indicated are the number of T states for each M cycle, as shown in the following
example.
This example indicates that the instruction consists of two machine cycles. The first cycle
contains 4 clock periods/T states). The second cycle contains 3 clock periods, for a total of
7 clock periods/T states. The instruction executes in 1.75 microseconds.
In the register format of each of the instructions that follow, the most-significant bit to the
left and the least-significant bit to the right.
M Cycles T States E.T.
2 7(4,3) 4 MHz 1.75
Z80 Instruction Set UM008011-0816
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8-Bit Load Group
The following 8-bit load instructions are each described in this section. Simply click to
jump to an instruction’s description to learn more.
LD r, r'
– see page 71
LD r,n
– see page 72
LD r, (HL)
– see page 74
LD r, (IX+d)
– see page 75
LD r, (IY+d)
– see page 77
LD (HL), r
– see page 79
LD (IX+d), r
– see page 81
LD (IY+d), r
– see page 83
LD (HL), n
– see page 85
LD (IX+d), n
– see page 86
LD (IY+d), n
– see page 87
LD A, (BC)
– see page 88
LD A, (DE)
– see page 89
LD A, (nn)
– see page 90
LD (BC), A
– see page 91
LD (DE), A
– see page 92
LD (nn), A
– see page 93
LD A, I
– see page 94
LD A, R
– see page 95
LD I,A
– see page 96
LD R, A
– see page 97
UM008011-0816 Z80 Instruction Description
Z80 CPU
User Manual
71
LD r, r'
Operation
r, ← r′
Op Code
LD
Operands
r, r′
Description
The contents of any register r' are loaded to any other register r. r, r' identifies any of the
registers A, B, C, D, E, H, or L, assembled as follows in the object code:
Condition Bits Affected
None.
Example
If the H Register contains the number 8Ah, and the E register contains 10h, the instruction
LD H, E results in both registers containing
10h.
Register r, C
A 111
B 000
C 001
D 010
E 011
H 100
L 101
M Cycles T States MHz E.T.
141.0
01 r
r'
Z80 Instruction Set UM008011-0816
72
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User Manual
LD r,n
Operation
r ← n
Op Code
LD
Operands
r, n
Description
The 8-bit integer n is loaded to any register r, in which r identifies registers A, B, C, D, E,
H, or L, assembled as follows in the object code:
Condition Bits Affected
None.
Register r
A 111
B 000
C 001
D 010
E 011
H 100
L 101
M Cycles T States 4 MHz E.T.
2 7 (4, 3) 1.75
00 r 101
n
UM008011-0816 Z80 Instruction Description
Z80 CPU
User Manual
73
Example
Upon the execution of an LD E, A5h instruction, Register E contains A5h.
Z80 Instruction Set UM008011-0816
74
Z80 CPU
User Manual
LD r, (HL)
Operation
r ← (HL)
Op Code
LD
Operands
r, (HL)
Description
The 8-bit contents of memory location (HL) are loaded to register r, in which r identifies
registers A, B, C, D, E, H, or L, assembled as follows in the object code:
Condition Bits Affected
None.
Example
If register pair HL contains the number 75A1h, and memory address 75A1h contains byte
58h, the execution of LD C, (HL) results in 58h in Register C.
Register r
A 111
B 000
C 001
D 010
E 011
H 100
L 101
M Cycles T States 4 MHz E.T.
2 7 (4, 3) 1.75
01 r 101
UM008011-0816 Z80 Instruction Description
Z80 CPU
User Manual
75
LD r, (IX+d)
Operation
r ← (IX+d)
Op Code
LD
Operands
r, (IX+d)
Description
The (IX+d) operand (i.e., the contents of Index Register IX summed with two’s-comple-
ment displacement integer d) is loaded to register r, in which r identifies registers A, B, C,
D, E, H, or L, assembled as follows in the object code:
Condition Bits Affected
None.
Register r
A 111
B 000
C 001
D 010
E 011
H 100
L 101
M Cycles T States 4 MHz E.T.
5 19 (4, 4, 3, 5,
3)
2.50
d
01 r 101
11 1 01101
DD
Z80 Instruction Set UM008011-0816
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User Manual
Example
If Index Register IX contains the number 25AFh, the instruction LD B, (IX+19h) allows
the calculation of the sum
25AFh + 19h, which points to memory location 25C8h. If this
address contains byte
39h, the instruction results in Register B also containing 39h.
UM008011-0816 Z80 Instruction Description
Z80 CPU
User Manual
77
LD r, (IY+d)
Operation
r ← (IY+D)
Op Code
LD
Operands
r, (lY+d)
Description
The operand (lY+d) loads the contents of Index Register IY summed with two’s-comple-
ment displacement integer, d, to register r, in which r identifies registers A, B, C, D, E, H,
or L, assembled as follows in the object code:
Condition Bits Affected
None.
Register r
A 111
B 000
C 001
D 010
E 011
H 100
L 101
M Cycles T States 4 MHz E.T.
5 19 (4, 4, 3, 5, 3) 4.75
d
01 r 101
11 1 01111
FD
Z80 Instruction Set UM008011-0816
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User Manual
Example
If Index Register IY contains the number 25AFh, the instruction LD B, (IY+19h) allows
the calculation of the sum
25AFh + 19h, which points to memory location 25C8h. If this
address contains byte
39h, the instruction results in Register B also containing 39h.
UM008011-0816 Z80 Instruction Description
Z80 CPU
User Manual
79
LD (HL), r
Operation
(HL) ← r
Op Code
LD
Operands
(HL), r
Description
The contents of register r are loaded to the memory location specified by the contents of
the HL register pair. The r symbol identifies registers A, B, C, D, E, H, or L, assembled as
follows in the object code:
Condition Bits Affected
None.
Register r
A 111
B 000
C 001
D 010
E 011
H 100
L 101
M Cycles T States 4 MHz E.T.
2 7 (4, 3) 1.75
01 1 r10
Z80 Instruction Set UM008011-0816
80
Z80 CPU
User Manual
Example
If the contents of register pair HL specify memory location 2146h and Register B contains
byte
29h, then upon the execution of an LD (HL), B instruction, memory address 2146h
also contains
29h.
UM008011-0816 Z80 Instruction Description
Z80 CPU
User Manual
81
LD (IX+d), r
Operation
(IX+d) ← r
Op Code
LD
Operands
(IX+d), r
Description
The contents of register r are loaded to the memory address specified by the contents of
Index Register IX summed with d, a two’s-complement displacement integer. The r sym-
bol identifies registers A, B, C, D, E, H, or L, assembled as follows in the object code:
Condition Bits Affected
None.
Register r
A 111
B 000
C 001
D 010
E 011
H 100
L 101
M Cycles T States 4 MHz E.T.
5 19 (4, 4, 3, 5, 3) 4.75
d
11 1 01101
DD
01 1 r10
Z80 Instruction Set UM008011-0816
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User Manual
Example
If the C register contains byte 1Ch, and Index Register IX contains 3100h, then the
instruction LID (IX +
6h), C performs the sum 3100h + 6h and loads 1Ch to memory
location
3106h.
UM008011-0816 Z80 Instruction Description
Z80 CPU
User Manual
83
LD (IY+d), r
Operation
(lY+d) ← r
Op Code
LD
Operands
(lY+d), r
Description
The contents of resister r are loaded to the memory address specified by the sum of the
contents of Index Register IY and d, a two’s-complement displacement integer. The r sym-
bol is specified according to the following table.
Condition Bits Affected
None.
Register r
A 111
B 000
C 001
D 010
E 011
H 100
L 101
M Cycles T States 4 MHz E.T.
5 19 (4, 4, 3, 5, 3) 4.75
d
11 1 01111
FD
01 1 r10
Z80 Instruction Set UM008011-0816
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User Manual
Example
If the C register contains byte 48h, and Index Register IY contains 2A11h, then the
instruction LD (IY +
4h), C performs the sum 2A11h + 4h, and loads 48h to memory
location
2A15.
UM008011-0816 Z80 Instruction Description
Z80 CPU
User Manual
85
LD (HL), n
Operation
(HL) ← n
Op Code
LD
Operands
(HL), n
Description
The n integer is loaded to the memory address specified by the contents of the HL register
pair.
Condition Bits Affected
None.
Example
If the HL register pair contains 4444h, the instruction LD (HL), 28h results in the mem-
ory location
4444h containing byte 28h.
M Cycles T States 4 MHz E.T.
3 10 (4, 3, 3) 2.50
n
00 1 10110
36
Z80 Instruction Set UM008011-0816
86
Z80 CPU
User Manual
LD (IX+d), n
Operation
(IX+d) ← n
Op Code
LD
Operands
(IX+d), n
Description
The n operand is loaded to the memory address specified by the sum of Index Register IX
and the two’s complement displacement operand d.
Condition Bits Affected
None.
Example
If Index Register IX contains the number 219Ah, then upon execution of an LD (IX+5h),
5Ah instruction, byte 5Ah is contained in memory address 219Fh.
M Cycles T States 4 MHz E.T.
5 19 (4, 4, 3,5,3) 4.75
d
11 1 01101
DD
n
00 1 10110
36
UM008011-0816 Z80 Instruction Description
Z80 CPU
User Manual
87
LD (IY+d), n
Operation
(lY+d) ← n
Op Code
LD
Operands
(lY+d), n
Description
The n integer is loaded to the memory location specified by the contents of Index Register
summed with the two’s-complement displacement integer, d.
Condition Bits Affected
None.
Example
If Index Register IY contains the number A940h, the instruction LD (IY+10h), 97h
results in byte 97h in memory location A950h.
M Cycles T States 4 MHz E.T.
5 19 (4, 4, 3, 5, 3) 2.50
d
11 1 01111
FD
n
00 1 10110
36
Z80 Instruction Set UM008011-0816
88
Z80 CPU
User Manual
LD A, (BC)
Operation
A ← (BC)
Op Code
LD
Operands
A, (BC)
Description
The contents of the memory location specified by the contents of the BC register pair are
loaded to the Accumulator.
Condition Bits Affected
None.
Example
If the BC register pair contains the number 4747h, and memory address 4747h contains
byte
12h, then the instruction LD A, (BC) results in byte 12h in Register A.
M Cycles T States 4 MHz E.T.
2 7 (4, 3) 1.75
00 0 10001
0A
UM008011-0816 Z80 Instruction Description
Z80 CPU
User Manual
89
LD A, (DE)
Operation
A ← (DE)
Op Code
LD
Operands
A, (DE)
Description
The contents of the memory location specified by the register pair DE are loaded to the
Accumulator.
Condition Bits Affected
None.
Example
If the DE register pair contains the number 30A2h and memory address 30A2h contains
byte
22h, then the instruction LD A, (DE) results in byte 22h in Register A.
M Cycles T States 4 MHz E.T.
2 7 (4, 3) 1.75
00 1 10001
1A
Z80 Instruction Set UM008011-0816
90
Z80 CPU
User Manual
LD A, (nn)
Operation
A ← (nn)
Op Code
LD
Operands
A, (nn)
Description
The contents of the memory location specified by the operands nn are loaded to the Accu-
mulator. The first n operand after the op code is the low-order byte of a 2-byte memory
address.
Condition Bits Affected
None.
Example
If nn contains 8832h and memory address 8832h contains byte 04h, then upon the execu-
tion of an LD A, (nn) instruction, the
04h byte is in the Accumulator.
M Cycles T States 4 MHz E.T.
4 13 (4, 3, 3, 3) 3.25
n
00 1 10011
3A
n
UM008011-0816 Z80 Instruction Description
Z80 CPU
User Manual
91
LD (BC), A
Operation
(BC) ← A
Op Code
LD
Operands
(BC), A
Description
The contents of the Accumulator are loaded to the memory location specified by the con-
tents of the register pair BC.
Condition Bits Affected
None.
Example
If the Accumulator contains 7Ah and the BC register pair contains 1212h the instruction
LD (BC), A results in
7Ah in memory location 1212h.
M Cycles T States 4 MHz E.T.
2 7 (4, 3) 1.75
00 0 10000
02
Z80 Instruction Set UM008011-0816
92
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User Manual
LD (DE), A
Operation
(DE) ← A
Op Code
LD
Operands
(DE), A
Description
The contents of the Accumulator are loaded to the memory location specified by the con-
tents of the DE register pair.
Condition Bits Affected
None.
Example
If register pair DE contains 1128h and the Accumulator contains byte A0h, then the exe-
cution of a LD (DE), A instruction results in
A0h being stored in memory location 1128h.
M Cycles T States 4 MHz E.T.
2 7 (4, 3) 1.75
00 1 10000
12
UM008011-0816 Z80 Instruction Description
Z80 CPU
User Manual
93
LD (nn), A
Operation
(nn) ← A
Op Code
LD
Operands
(nn), A
Description
The contents of the Accumulator are loaded to the memory address specified by the oper-
and nn. The first n operand after the op code is the low-order byte of nn.
Condition Bits Affected
None.
Example
If the Accumulator contains byte D7h, then executing an LD (3141h), AD7h instruction
results in memory location
3141h.
M Cycles T States 4 MHz E.T.
4 13 (4, 3, 3, 3) 3.25
n
00 1 10010
32
n
Z80 Instruction Set UM008011-0816
94
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User Manual
LD A, I
Operation
A ← 1
Op Code
LD
Operands
A, I
Description
The contents of the Interrupt Vector Register I are loaded to the Accumulator.
Condition Bits Affected
S is set if the I Register is negative; otherwise, it is reset.
Z is set if the I Register is 0; otherwise, it is reset.
H is reset.
P/V contains contents of IFF2.
N is reset.
C is not affected.
If an interrupt occurs during execution of this instruction, the Parity flag contains a 0.
M Cycles T States MHz E.T.
2 9 (4, 5) 2.25
11 0 01111
ED
01 1 11100
57
UM008011-0816 Z80 Instruction Description
Z80 CPU
User Manual
95
LD A, R
Operation
A ← R
Op Code
LD
Operands
A, R
Description
The contents of Memory Refresh Register R are loaded to the Accumulator.
Condition Bits Affected
S is set if, R-Register is negative; otherwise, it is reset.
Z is set if the R Register is 0; otherwise, it is reset.
H is reset.
P/V contains contents of IFF2.
N is reset.
C is not affected.
If an interrupt occurs during execution of this instruction, the parity flag contains a 0.
M Cycles T States MHz E.T.
2 9 (4, 5) 2.25
11 0 01111
ED
01 1 11101
5F
Z80 Instruction Set UM008011-0816
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User Manual
LD I,A
Operation
I ← A
Op Code
LD
Operands
I, A
Description
The contents of the Accumulator are loaded to the Interrupt Control Vector Register, I.
Condition Bits Affected
None.
M Cycles T States MHz E.T.
2 9 (4, 5) 2.25
11 0 01111
ED
01 0 11100
47
UM008011-0816 Z80 Instruction Description
Z80 CPU
User Manual
97
LD R, A
Operation
R ← A
Op Code
LD
Operands
R, A
Description
The contents of the Accumulator are loaded to the Memory Refresh register R.
Condition Bits Affected
None.
M Cycles T States MHz E.T.
2 9 (4, 5) 2.25
11 0 01111
ED
01 0 11101
4F
Z80 Instruction Set UM008011-0816
98
Z80 CPU
User Manual
16-Bit Load Group
The following 16-bit load instructions are each described in this section. Simply click to
jump to an instruction’s description to learn more.
LD dd, nn
– see page 99
LD IX, nn
– see page 100
LD IY, nn
– see page 101
LD HL, (nn)
– see page 102
LD dd, (nn)
– see page 103
LD IX, (nn)
– see page 105
LD IY, (nn)
– see page 106
LD (nn), HL
– see page 107
LD (nn), dd
– see page 108
LD (nn), IX
– see page 110
LD (nn), IY
– see page 111
LD SP, HL
– see page 112
LD SP, IX
– see page 113
LD SP, IY
– see page 114
PUSH qq
– see page 115
PUSH IX
– see page 117
PUSH IY
– see page 118
POP qq
– see page 119
POP IX
– see page 121
POP IY
– see page 122
UM008011-0816 Z80 Instruction Description
Z80 CPU
User Manual
99
LD dd, nn
Operation
dd ← nn
Op Code
LD
Operands
dd, nn
Description
The 2-byte integer nn is loaded to the dd register pair, in which dd defines the BC, DE,
HL, or SP register pairs, assembled as follows in the object code:
The first n operand after the op code is the low-order byte.
Condition Bits Affected
None.
Example
Upon the execution of an LD HL, 5000h instruction, the HL register pair contains 5000h.
Pair dd
BC 00
DE 01
HL 10
SP 11
M Cycles T States 4 MHz E.T.
2 10 (4, 3, 3) 2.50
n
00 d 010d0
n
Z80 Instruction Set UM008011-0816
100
Z80 CPU
User Manual
LD IX, nn
Operation
IX ← nn
Op Code
LD
Operands
IX, nn
Description
The n integer is loaded to Index Register IX. The first n operand after the op code is the
low-order byte.
Condition Bits Affected
None.
Example
Upon the execution of an LD IX, 45A2h instruction, the index register contains integer
45A2h.
M Cycles T States 4 MHz E.T.
4 14 (4, 4, 3, 3) 3.50
11 1 01101
DD
00 0 01010
21
n
n
UM008011-0816 Z80 Instruction Description
Z80 CPU
User Manual
101
LD IY, nn
Operation
IY ← nn
Op Code
LD
Operands
IY, nn
Description
The nn integer is loaded to Index Register IY. The first n operand after the op code is the
low-order byte.
Condition Bits Affected
None.
Example
Upon the execution of a LD IY, 7733h instruction, Index Register IY contains the integer
7733h.
M Cycles T States 4 MHz E.T.
4 14 (4, 4, 3, 3) 3.50
11 1 01111
FD
00 0 01010
21
n
n
Z80 Instruction Set UM008011-0816
102
Z80 CPU
User Manual
LD HL, (nn)
Operation
H ← (nn + 1), L ← (nn)
Op Code
LD
Operands
HL, (nn)
Description
The contents of memory address (nn) are loaded to the low-order portion of register pair
HL (Register L), and the contents of the next highest memory address (nn + 1) are loaded
to the high-order portion of HL (Register H). The first n operand after the op code is the
low-order byte of nn.
Condition Bits Affected
None.
Example
If address 4545h contains 37h and address 4546h contains A1h, then upon the execution
of an LD HL, (
4545h) instruction, the HL register pair contains A137h.
M Cycles T States 4 MHz E.T.
5 16 (4, 3, 3, 3, 3) 4.00
00 0 10011
2A
n
n
UM008011-0816 Z80 Instruction Description
Z80 CPU
User Manual
103
LD dd, (nn)
Operation
ddh ← (nn + 1) ddl ← (nn)
Op Code
LD
Operands
dd, (nn)
Description
The contents of address (nn) are loaded to the low-order portion of register pair dd, and the
contents of the next highest memory address (nn + 1) are loaded to the high-order portion
of dd. Register pair dd defines BC, DE, HL, or SP register pairs, assembled as follows in
the object code:
The first n operand after the op code is the low-order byte of (nn).
Condition Bits Affected
None.
Pair dd
BC 00
DE 01
HL 10
SP 11
M Cycles T States 4 MHz E.T.
6 20 (4, 4, 3, 3, 3, 3) 5.00
11 0 01111
ED
01 d 110d1
n
n
Z80 Instruction Set UM008011-0816
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User Manual
Example
If Address 2130h contains 65h and address 2131h contains 78h, then upon the execution
of an LD BC, (
2130h) instruction, the BC register pair contains 7865h.
UM008011-0816 Z80 Instruction Description
Z80 CPU
User Manual
105
LD IX, (nn)
Operation
IXh ← (nn + 1), IXI ← (nn)
Op Code
LD
Operands
IX, (nn)
Description
The contents of the address (nn) are loaded to the low-order portion of Index Register IX,
and the contents of the next highest memory address (nn + 1) are loaded to the high-order
portion of IX. The first n operand after the op code is the low-order byte of nn.
Condition Bits Affected
None.
Example
If address 6666h contains 92h, and address 6667h contains DAh, then upon the execution
of an LD IX, (
6666h) instruction, Index Register IX contains DA92h.
M Cycles T States 4 MHz E.T.
6 20 (4, 4, 3, 3, 3, 3) 5.00
11 1 01101
DD
00 0 10011
2A
n
n
Z80 Instruction Set UM008011-0816
106
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User Manual
LD IY, (nn)
Operation
IYh ← (nn + 1), IYI ← nn)
Op Code
LD
Operands
IY, (nn)
Description
The contents of address (nn) are loaded to the low-order portion of Index Register IY, and
the contents of the next highest memory address (nn + 1) are loaded to the high-order por-
tion of IY. The first n operand after the op code is the low-order byte of nn.
Condition Bits Affected
None.
Example
If address 6666h contains 92h, and address 6667h contains DAh, then upon the execution
of an LD IY, (
6666h) instruction, Index Register IY contains DA92h.
M Cycles T States 4 MHz E.T.
6 20 (4, 4, 3, 3, 3, 3) 5.00
11 1 01111
FD
00 0 10011
2A
n
n
UM008011-0816 Z80 Instruction Description
Z80 CPU
User Manual
107
LD (nn), HL
Operation
(nn + 1) ← H, (nn) ← L
Op Code
LD
Operands
(nn), HL
Description
The contents of the low-order portion of register pair HL (Register L) are loaded to mem-
ory address (nn), and the contents of the high-order portion of HL (Register H) are loaded
to the next highest memory address (nn + 1). The first n operand after the op code is the
low-order byte of nn.
Condition Bits Affected
None.
Example
If register pair HL contains 483Ah, then upon the execution of an LD (B2291 – 1), HL
instruction, address
B229h contains 3Ah and address B22Ah contains 48h.
M Cycles T States 4 MHz E.T.
5 16 (4, 3, 3, 3, 3) 4.00
00 0 10010
22
n
n
Z80 Instruction Set UM008011-0816
108
Z80 CPU
User Manual
LD (nn), dd
Operation
(nn + 1) ← ddh, (nn) ← ddl
Op Code
LD
Operands
(nn), dd
Description
The low-order byte of register pair dd is loaded to memory address (nn); the upper byte is
loaded to memory address (nn + 1). Register pair dd defines either BC, DE, HL, or SP,
assembled as follows in the object code:
The first n operand after the op code is the low-order byte of a two byte memory address.
Condition Bits Affected
None.
Pair dd
BC 00
DE 01
HL 10
SP 11
M Cycles T States 4 MHz E.T.
6 20 (4, 4, 3, 3, 3, 3) 5.00
11 0 01111
ED
01 d 110d0
n
n
UM008011-0816 Z80 Instruction Description
Z80 CPU
User Manual
109
Example
If register pair BC contains the number 4644h, the instruction LD (1000h), BC results in
44h in memory location 1000h, and 46h in memory location 1001h.
Z80 Instruction Set UM008011-0816
110
Z80 CPU
User Manual
LD (nn), IX
Operation
(nn + 1) ← IXh, (nn) ← IXI
Op Code
LD
Operands
(nn), IX
Description
The low-order byte in Index Register IX is loaded to memory address (nn); the upper order
byte is loaded to the next highest address (nn + 1). The first n operand after the op code is
the low-order byte of nn.
Condition Bits Affected
None.
Example
If Index Register IX contains 5A30h, then upon the execution of an LD (4392h), IX
instruction, memory location
4392h contains number 30h and location 4393h contains
5Ah.
M Cycles T States 4 MHz E.T.
6 20 (4, 4, 3, 3, 3, 3) 5.00
11 1 01101
DD
00 0 10010
22
n
n
UM008011-0816 Z80 Instruction Description
Z80 CPU
User Manual
111
LD (nn), IY
Operation
(nn + 1) ← IYh, (nn) ← IYI
Op Code
LD
Operands
(nn), IY
Description
The low-order byte in Index Register IY is loaded to memory address (nn); the upper order
byte is loaded to memory location (nn + 1). The first n operand after the op code is the low-
order byte of nn.
Condition Bits Affected
None.
Example
If Index Register IY contains 4174h, then upon the execution of an LD (8838h), IY
instruction, memory location
8838h contains 74h and memory location 8839h contains
41h.
M Cycles T States 4 MHz E.T.
6 20 (4, 4, 3, 3, 3, 3) 5.00
11 1 01111
FD
00 0 10010
22
n
n
Z80 Instruction Set UM008011-0816
112
Z80 CPU
User Manual
LD SP, HL
Operation
SP ← HL
Op Code
LD
Operands
SP, HL
Description
The contents of the register pair HL are loaded to the Stack Pointer (SP).
Condition Bits Affected
None.
Example
If the register pair HL contains 442Eh, then upon the execution of an LD SP, HL instruc-
tion, the Stack Pointer also contains
442Eh.
M Cycles T States 4 MHz E.T.
16 1.5
11 1 01011
F9
UM008011-0816 Z80 Instruction Description
Z80 CPU
User Manual
113
LD SP, IX
Operation
SP ← IX
Op Code
LD
Operands
SP, IX
Description
The 2-byte contents of Index Register IX are loaded to the Stack Pointer (SP).
Condition Bits Affected
None.
Example
If Index Register IX contains 98DAh, then upon the execution of an LD SP, IX instruction,
the Stack Pointer also contains
98DAh.
M Cycles T States 4 MHz E.T.
2 10 (4, 6) 2.50
11 1 01101
DD
11 1 01011
F9
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LD SP, IY
Operation
SP ← IY
Op Code
LD
Operands
SP, IY
Description
The 2-byte contents of Index Register IY are loaded to the Stack Pointer SP.
Condition Bits Affected
None.
Example
If Index Register IY contains the integer A227h, then upon the execution of an LD SP, IY
instruction, the Stack Pointer also contains
A227h.
M Cycles T States 4 MHz E.T.
2 10 (4, 6) 2.50
11 1 01111
FD
11 1 01011
F9
UM008011-0816 Z80 Instruction Description
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115
PUSH qq
Operation
(SP – 2) ← qqL, (SP – 1) ← qqH
Op Code
PUSH
Operand
qq
Description
The contents of the register pair qq are pushed to the external memory last-in, first-out
(LIFO) stack. The Stack Pointer (SP) Register pair holds the 16-bit address of the current
top of the Stack. This instruction first decrements SP and loads the high-order byte of reg-
ister pair qq to the memory address specified by the SP. The SP is decremented again and
loads the low-order byte of qq to the memory location corresponding to this new address
in the SP. The operand qq identifies register pair BC, DE, HL, or AF, assembled as follows
in the object code:
Condition Bits Affected
None.
Pair qq
BC 00
DE 01
HL 10
AF 11
M Cycles T States 4 MHz E.T.
3 11 (5, 3, 3) 2.75
11 q 011q0
Z80 Instruction Set UM008011-0816
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Example
If the AF Register pair contains 2233h and the Stack Pointer contains 1007h, then upon
the execution of a PUSH AF instruction, memory address
1006h contains 22h, memory
address
1005h contains 33h, and the Stack Pointer contains 1005h.
UM008011-0816 Z80 Instruction Description
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117
PUSH IX
Operation
(SP – 2) ← IXL, (SP – 1) ← IXH
Op Code
PUSH
Operand
IX
Description
The contents of Index Register IX are pushed to the external memory last-in, first-out
(LIFO) stack. The Stack Pointer (SP) Register pair holds the 16-bit address of the current
top of the Stack. This instruction first decrements SP and loads the high-order byte of IX
to the memory address specified by SP; then decrements SP again and loads the low-order
byte to the memory location corresponding to this new address in SP.
Condition Bits Affected
None.
Example
If Index Register IX contains 2233h and the Stack Pointer contains 1007h, then upon the
execution of a PUSH IX instruction, memory address
1006h contains 22h, memory
address
1005h contains 33h, and the Stack Pointer contains 1005h.
M Cycles T States 4 MHz E.T.
4 15 (4, 5, 3, 3) 3.75
11 1 01101
DD
11 0 01110
E5
Z80 Instruction Set UM008011-0816
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PUSH IY
Operation
(SP – 2) ← IYL, (SP – 1) ← IYH
Op Code
PUSH
Operand
IY
Description
The contents of Index Register IY are pushed to the external memory last-in, first-out
(LIFO) stack. The Stack Pointer (SP) Register pair holds the 16-bit address of the current
top of the Stack. This instruction first decrements the SP and loads the high-order byte of
IY to the memory address specified by SP; then decrements SP again and loads the low-
order byte to the memory location corresponding to this new address in SP.
Condition Bits Affected
None.
Example
If Index Register IY contains 2233h and the Stack Pointer contains 1007h, then upon the
execution of a PUSH IY instruction, memory address
1006h contains 22h, memory
address
1005h contains 33h, and the Stack Pointer contains 1005h.
M Cycles T States 4 MHz E.T.
4 15 (4, 5, 3, 3) 3.75
11 1 01111
FD
11 0 01110
E5
UM008011-0816 Z80 Instruction Description
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119
POP qq
Operation
qqH ← (SP+1), qqL ← (SP)
Op Code
POP
Operand
qq
Description
The top two bytes of the external memory last-in, first-out (LIFO) stack are popped to reg-
ister pair qq. The Stack Pointer (SP) Register pair holds the 16-bit address of the current
top of the Stack. This instruction first loads to the low-order portion of qq, the byte at the
memory location corresponding to the contents of SP; then SP is incremented and the con-
tents of the corresponding adjacent memory location are loaded to the high-order portion
of qq and the SP is now incremented again. The operand qq identifies register pair BC,
DE, HL, or AF, assembled as follows in the object code:
Condition Bits Affected
None.
Pair r
BC 00
DE 01
HL 10
AF 11
M Cycles T States 4 MHz E.T.
3 10 (4, 3, 3) 2.50
11 q 010q0
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Example
If the Stack Pointer contains 1000h, memory location 1000h contains 55h, and location
1001h contains 33h, the instruction POP HL results in register pair HL containing 3355h,
and the Stack Pointer containing
1002h.
UM008011-0816 Z80 Instruction Description
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121
POP IX
Operation
IXH ← (SP+1), IXL ← (SP)
Op Code
POP
Operand
IX
Description
The top two bytes of the external memory last-in, first-out (LIFO) stack are popped to
Index Register IX. The Stack Pointer (SP) Register pair holds the 16-bit address of the
current top of the Stack. This instruction first loads to the low-order portion of IX the byte
at the memory location corresponding to the contents of SP; then SP is incremented and
the contents of the corresponding adjacent memory location are loaded to the high-order
portion of IX. The SP is incremented again.
Condition Bits Affected
None.
Example
If the Stack Pointer contains 1000h, memory location 1000h contains 55h, and location
1001h contains 33h, the instruction POP IX results in Index Register IX containing
3355h, and the Stack Pointer containing 1002h.
M Cycles T States 4 MHz E.T.
4 14 (4, 4, 3, 3) 3.50
11 1 01101
DD
11 0 01010
E1
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POP IY
Operation
IYH ← (SP – X1), IYL ← (SP)
Op Code
POP
Operand
IY
Description
The top two bytes of the external memory last-in, first-out (LIFO) stack are popped to
Index Register IY. The Stack Pointer (SP) Register pair holds the 16-bit address of the cur-
rent top of the Stack. This instruction first loads to the low-order portion of IY the byte at
the memory location corresponding to the contents of SP; then SP is incremented and the
contents of the corresponding adjacent memory location are loaded to the high-order por-
tion of IY. The SP is incremented again.
Condition Bits Affected
None.
Example
If the Stack Pointer Contains 1000h, memory location 1000h contains 55h, and location
1001h contains 33h, the instruction POP IY results in Index Register IY containing
3355h, and the Stack Pointer containing 1002h.
M Cycles T States 4 MHz E.T.
4 14 (4, 4, 3, 3) 3.50
11 1 01111
FD
11 0 01010
E1
UM008011-0816 Z80 Instruction Description
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123
Exchange, Block Transfer, and Search Group
The following exchange, block transfer, and search group instructions are each described
in this section. Simply click to jump to an instruction’s description to learn more.
EX DE, HL
– see page 124
EX AF, AF′
– see page 125
EXX
– see page 126
EX (SP), HL
– see page 127
EX (SP), IX
– see page 128
EX (SP), IY
– see page 129
LDI
– see page 130
LDIR
– see page 132
LDD
– see page 134
LDDR
– see page 136
CPI
– see page 138
CPIR
– see page 139
CPD
– see page 141
CPDR
– see page 142
Z80 Instruction Set UM008011-0816
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EX DE, HL
Operation
DE ↔ HL
Op Code
EX
Operands
DE, HL
Description
The 2-byte contents of register pairs DE and HL are exchanged.
Condition Bits Affected
None.
Example
If register pair DE contains 2822h and register pair HL contains 499Ah, then upon the
execution of an EX DE, HL instruction, register pair DE contains
499Ah and register pair
HL contains
2822h.
M Cycles T States 4 MHz E.T.
141.00
11 0 11011
EB
UM008011-0816 Z80 Instruction Description
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125
EX AF, AF′
Operation
AF ↔ AF'
Op Code
EX
Operands
AF, AF′
Description
The 2-byte contents of the register pairs AF and AF' are exchanged. Register pair AF con-
sists of registers A′ and F′.
Condition Bits Affected
None.
Example
If register pair AF contains 9900h and register pair AF′ contains 5944h, the contents of
AF are
5944h and the contents of AF′ are 9900h upon execution of the EX AF, AF′
instruction.
M Cycles T States 4 MHz E.T.
141.00
00 0 00001
08
Z80 Instruction Set UM008011-0816
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EXX
Operation
(BC) ↔ (BC′), (DE) ↔ (DE'), (HL) ↔ (HL′)
Op Code
EXX
Operands
None.
Description
Each 2-byte value in register pairs BC, DE, and HL is exchanged with the 2-byte value in
BC', DE', and HL', respectively.
Condition Bits Affected
None.
Example
If register pairs BC, DE, and HL contain 445Ah, 3DA2h, and 8859h, respectively, and
register pairs BC’, DE’, and HL’ contain
0988h, 9300h, and 00E7h, respectively, then
upon the execution of an EXX instruction, BC contains
0988h; DE contains 9300h; HL
contains
00E7h; BC’ contains 445Ah; DE’ contains 3DA2h; and HL’ contains 8859h.
M Cycles T States 4 MHz E.T.
141.00
11 1 01001
D9
UM008011-0816 Z80 Instruction Description
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127
EX (SP), HL
Operation
H ↔ (SP+1), L ↔ (SP)
Op Code
EX
Operands
(SP), HL
Description
The low-order byte contained in register pair HL is exchanged with the contents of the
memory address specified by the contents of register pair SP (Stack Pointer), and the high-
order byte of HL is exchanged with the next highest memory address (SP+1).
Condition Bits Affected
None.
Example
If the HL register pair contains 7012h, the SP register pair contains 8856h, the memory
location
8856h contains byte 11h, and memory location 8857h contains byte 22h, then
the instruction EX (SP), HL results in the HL register pair containing number
2211h,
memory location
8856h containing byte 12h, memory location 8857h containing byte
70h and Stack Pointer containing 8856h.
M Cycles T States 4 MHz E.T.
5 19 (4, 3, 4, 3, 5) 4.75
11 0 11010
E3
Z80 Instruction Set UM008011-0816
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EX (SP), IX
Operation
IXH ↔ (SP+1), IXL ↔ (SP)
Op Code
EX
Operands
(SP), IX
Description
The low-order byte in Index Register IX is exchanged with the contents of the memory
address specified by the contents of register pair SP (Stack Pointer), and the high-order
byte of IX is exchanged with the next highest memory address (SP+1).
Condition Bits Affected
None.
Example
If Index Register IX contains 3988h, the SP register pair Contains 0100h, memory loca-
tion
0100h contains byte 90h, and memory location 0101h contains byte 48h, then the
instruction EX (SP), IX results in the IX register pair containing number
4890h, memory
location
0100h containing 88h, memory location 0101h containing 39h, and the Stack
Pointer containing
0100h.
M Cycles T States 4 MHz E.T.
6 23 (4, 4, 3, 4, 3, 5) 5.75
11 1 01101
DD
11 0 11010
E3
UM008011-0816 Z80 Instruction Description
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129
EX (SP), IY
Operation
IYH ↔ (SP+1), IYL ↔ (SP)
Op Code
EX
Operands
(SP), IY
Description
The low-order byte in Index Register IY is exchanged with the contents of the memory
address specified by the contents of register pair SP (Stack Pointer), and the high-order
byte of IY is exchanged with the next highest memory address (SP+1).
Condition Bits Affected
None.
Example
If Index Register IY contains 3988h, the SP register pair contains 0100h, memory loca-
tion
0100h contains byte 90h, and memory location 0101h contains byte 48h, then the
instruction EX (SP), IY results in the IY register pair containing number
4890h, memory
location
0100h containing 88h, memory location 0101h containing 39h, and the Stack
Pointer containing
0100h.
M Cycles T States 4 MHz E.T.
6 23 (4, 4, 3, 4, 3, 5) 5.75
11 1 01111
FD
11 0 11010
E3
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LDI
Operation
(DE) ← (HL), DE ← DE + 1, HL ← HL + 1, BC ← BC – 1
Op Code
LDI
Operands
None
Description
A byte of data is transferred from the memory location addressed, by the contents of the
HL register pair to the memory location addressed by the contents of the DE register pair.
Then both these register pairs are incremented and the Byte Counter (BC) Register pair is
decremented.
Condition Bits Affected
S is not affected.
Z is not affected.
H is reset.
P/V is set if BC – 1 ≠ 0; otherwise, it is reset.
N is reset.
C is not affected.
Example
If the HL register pair contains 1111h, memory location 1111h contains byte 88h, the DE
register pair contains
2222h, the memory location 2222h contains byte 66h, and the BC
M Cycles T States 4 MHz E.T.
4 16 (4, 4, 3, 5) 4.00
11 0 01111
ED
10 0 00010
A0
UM008011-0816 Z80 Instruction Description
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131
register pair contains 7h, then the instruction LDI results in the following contents in reg-
ister pairs and memory addresses:
HL contains 1112h
(1111h) contains 88h
DE contains 2223h
(2222h) contains 88h
BC contains 6H
Z80 Instruction Set UM008011-0816
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LDIR
Operation
repeat {(DE) ← (HL), DE ← DE + 1, HL ← HL + 1, BC ← BC – 1} while (BC ≠ 0)
Op Code
LDIR
Operand
None
Description
This 2-byte instruction transfers a byte of data from the memory location addressed by the
contents of the HL register pair to the memory location addressed by the DE register pair.
Both these register pairs are incremented and the Byte Counter (BC) Register pair is dec-
remented. If decrementing allows the BC to go to 0, the instruction is terminated. If BC is
not 0, the program counter is decremented by two and the instruction is repeated. Inter-
rupts are recognized and two refresh cycles are executed after each data transfer. When the
BC is set to 0 prior to instruction execution, the instruction loops through 64 KB.
For BC ≠ 0:
For BC = 0:
Condition Bits Affected
S is not affected.
Z is not affected.
H is reset.
M Cycles T States 4 MHz E.T.
5 21 (4, 4, 3, 5, 5) 5.25
M Cycles T States 4 MHz E.T.
4 16 (4, 4, 3, 5) 4.00
11 0 01111
ED
10 1 00010
B0
UM008011-0816 Z80 Instruction Description
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P/V is set if BC – 1 ≠ 0; otherwise, it is reset.
N is reset.
C is not affected.
Example
The HL register pair contains 11111h, the DE register pair contains 2222h, the BC regis-
ter pair contains
0003h, and memory locations contain the following data.
Upon the execution of an LDIR instruction, the contents of register pairs and memory
locations now contain:
(1111h) contains 88h (2222h) contains 66h
(1112h) contains 36h (2223h) contains 59h
(1113h) contains A5h (2224h) contains C5h
HL contains 1114h
DE contains 2225h
BC contains 0000h
(1111h) contains 88h (2222h) contains 88h
(1112h) contains 36h (2223h) contains 36h
(1113h) contains A5h (2224h) contains A5h
Z80 Instruction Set UM008011-0816
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LDD
Operation
(DE) ← (HL), DE ← DE – 1, HL ← HL– 1, BC ← BC– 1
Op Code
LDD
Operands
None.
Description
This 2-byte instruction transfers a byte of data from the memory location addressed by the
contents of the HL register pair to the memory location addressed by the contents of the
DE register pair. Then both of these register pairs including the Byte Counter (BC) Regis-
ter pair are decremented.
Condition Bits Affected
S is not affected.
Z is not affected.
H is reset.
P/V is set if BC – 1 ≠ 0; otherwise, it is reset.
N is reset.
C is not affected.
Example
If the HL register pair contains 1111h, memory location 1111h contains byte 88h, the DE
register pair contains
2222h, memory location 2222h contains byte 66h, and the BC reg-
M Cycles T States 4 MHz E.T.
4 16 (4, 4, 3, 5) 4.00
11 0 01111
ED
10 0 00011
A8
UM008011-0816 Z80 Instruction Description
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135
ister pair contains 7h, then instruction LDD results in the following contents in register
pairs and memory addresses:
HL contains 1110h
(1111h) contains 88h
DE contains 2221h
(2222h) contains 88h
BC contains 6h
Z80 Instruction Set UM008011-0816
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LDDR
Operation
(DE) ← (HL), DE ← DE – 1, HL ← HL – 1, BC ← BC – 1
Op Code
LDDR
Operands
None.
Description
This 2-byte instruction transfers a byte of data from the memory location addressed by the
contents of the HL register pair to the memory location addressed by the contents of the
DE register pair. Then both of these registers, and the BC (Byte Counter), are decre-
mented. If decrementing causes BC to go to 0, the instruction is terminated. If BC is not 0,
the program counter is decremented by two and the instruction is repeated. Interrupts are
recognized and two refresh cycles execute after each data transfer.
When the BC is set to 0, prior to instruction execution, the instruction loops through
64 KB.
For BC ≠ 0:
For BC = 0:
M Cycles T States 4 MHz E.T.
5 21 (4, 4, 3, 5, 5) 5.25
M Cycles T States 4 MHz E.T.
4 16 (4, 4, 3, 5) 4.00
11 0 01111
ED
10 1 00011
B8
UM008011-0816 Z80 Instruction Description
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137
Condition Bits Affected
S is not affected.
Z is not affected.
H is reset.
P/V is reset.
N is reset.
Example
The HL register pair contains 1114h, the DE register pair contains 2225h, the BC register
pair contains
0003h, and memory locations contain the following data.
Upon the execution of an LDDR instruction, the contents of the register pairs and memory
locations now contain:
(1114h) contains A5h (2225h) contains C5h
(1113h) contains 36h (2224h) contains 59h
(1112h) contains 88h (2223h) contains 66h
HL contains 1111h
DE contains 2222h
DC contains 0000h
(1114h) contains A5h (2225h) contains A5h
(1113h) contains 36h (2224h) contains 36h
(1112h) contains 88h (2223h) contains 88h
Z80 Instruction Set UM008011-0816
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CPI
Operation
A – (HL), HL ← HL +1, BC ← BC – 1
Op Code
CPI
Operands
None.
Description
The contents of the memory location addressed by the HL register is compared with the
contents of the Accumulator. With a true compare, a condition bit is set. Then HL is incre-
mented and the Byte Counter (register pair BC) is decremented.
Condition Bits Affected
S is set if result is negative; otherwise, it is reset.
Z is set if A is (HL); otherwise, it is reset.
H is set if borrow from bit 4; otherwise, it is reset.
P/V is set if BC – 1 is not 0; otherwise, it is reset.
N is set.
C is not affected.
Example
If the HL register pair contains 1111h, memory location 1111h contains 3Bh, the Accu-
mulator contains
3Bh, and the Byte Counter contains 0001h. Upon the execution of a CPI
instruction, the Byte Counter contains
0000h, the HL register pair contains 1112h, the Z
flag in the F register is set, and the P/V flag in the F Register is reset. There is no effect on
the contents of the Accumulator or to address
1111h.
M Cycles T States 4 MHz E.T.
4 16 (4, 4, 3, 5) 4.00
11 0 01111
ED
10 0 01010
A1
UM008011-0816 Z80 Instruction Description
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139
CPIR
Operation
A – (HL), HL ← HL+1, BC ← BC – 1
Op Code
CPIR
Operands
None.
Description
The contents of the memory location addressed by the HL register pair is compared with
the contents of the Accumulator. During a compare operation, a condition bit is set. HL is
incremented and the Byte Counter (register pair BC) is decremented. If decrementing
causes BC to go to 0 or if A = (HL), the instruction is terminated. If BC is not 0 and A ≠
(HL), the program counter is decremented by two and the instruction is repeated. Inter-
rupts are recognized and two refresh cycles are executed after each data transfer.
If BC is set to 0 before instruction execution, the instruction loops through 64 KB if no
match is found.
For BC ≠ 0 and A ≠ (HL):
For BC = 0 and A = (HL):
M Cycles T States 4 MHz E.T.
5 21 (4, 4, 3, 5, 5) 5.25
M Cycles T States 4 MHz E.T.
4 16 (4, 4, 3, 5) 4.00
11 0 01111
ED
10 1 01010
B1
Z80 Instruction Set UM008011-0816
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Condition Bits Affected
S is set if result is negative; otherwise, it is reset.
Z is set if A equals (HL); otherwise, it is reset.
H is set if borrow from bit 4; otherwise, it is reset.
P/V is set if BC – 1 does not equal 0; otherwise, it is reset.
N is set.
C is not affected.
Example
If the HL register pair contains 1111h, the Accumulator contains F3h, the Byte Counter
contains
0007h, and memory locations contain the following data.
Upon the execution of a CPIR instruction, register pair HL contains
1114h, the Byte
Counter contains
0004h, the P/V flag in the F Register is set, and the Z flag in the F Reg-
ister is set.
(1111h) contains 52h
(1112h) contains 00h
(1113h) contains F3h
UM008011-0816 Z80 Instruction Description
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141
CPD
Operation
A – (HL), HL ← HL – 1, BC ← BC – 1
Op Code
CPD
Operands
None.
Description
The contents of the memory location addressed by the HL register pair is compared with
the contents of the Accumulator. During a compare operation, a condition bit is set. The
HL and Byte Counter (register pair BC) are decremented.
Condition Bits Affected
S is set if result is negative; otherwise, it is reset.
Z is set if A equals (HL); otherwise, it is reset.
H is set if borrow from bit 4; otherwise, it is reset.
P/V is set if BC – 1≠
0; otherwise, it is reset.
N is set.
C is not affected.
Example
If the HL register pair contains 1111h, memory location 1111h contains 3Bh, the Accu-
mulator contains
3Bh, and the Byte Counter contains 0001h. Upon the execution of a
CPD instruction, the Byte Counter contains
0000h, the HL register pair contains 1110h,
the flag in the F Register is set, and the P/V flag in the F Register is reset. There is no
effect on the contents of the Accumulator or address
1111h.
M Cycles T States 4 MHz E.T.
4 16 (4, 4, 3, 5) 4.00
11 0 01111
ED
10 0 01011
A9
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CPDR
Operation
A – (HL), HL ← HL – 1, BC ← BC – 1
Op Code
CPDR
Operands
None.
Description
The contents of the memory location addressed by the HL register pair is compared with
the contents of the Accumulator. During a compare operation, a condition bit is set. The
HL and Byte Counter (BC) Register pairs are decremented. If decrementing allows the BC
to go to 0 or if A = (HL), the instruction is terminated. If BC is not 0 and A = (HL), the
program counter is decremented by two and the instruction is repeated. Interrupts are rec-
ognized and two refresh cycles execute after each data transfer. When the BC is set to 0,
prior to instruction execution, the instruction loops through 64 KB if no match is found.
For BC ≠ 0 and A ≠ (HL):
For BC = 0 and A = (HL):
Condition Bits Affected
S is set if result is negative; otherwise, it is reset.
Z is set if A = (HL); otherwise, it is reset.
H is set if borrow form bit 4; otherwise, it is reset.
M Cycles T States 4 MHz E.T.
5 21 (4, 4, 3, 5, 5) 5.25
M Cycles T States 4 MHz E.T.
4 16 (4, 4, 3, 5) 4.00
11 0 01111
ED
10 1 01011
B9
UM008011-0816 Z80 Instruction Description
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143
P/V is set if BC – 1 ≠ 0; otherwise, it is reset.
N is set.
C is not affected.
Example
The HL register pair contains 1118h, the Accumulator contains F3h, the Byte Counter
contains
0007h, and memory locations contain the following data.
Upon the execution of a CPDR instruction, register pair HL contains
1115h, the Byte
Counter contains
0004h, the P/V flag in the F Register is set, and the Z flag in the F Reg-
ister is set.
(1118h) contains 52h
(1117h) contains 00h
(1116h) contains F3h
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8-Bit Arithmetic Group
The following 8-bit arithmetic group instructions are each described in this section. Sim-
ply click to jump to an instruction’s description to learn more.
ADD A, r
– see page 145
ADD A, n
– see page 147
ADD A, (HL)
– see page 148
ADD A, (IX + d)
– see page 149
ADD A, (IY + d)
– see page 150
ADC A, s
– see page 151
SUB s
– see page 153
SBC A, s
– see page 155
AND s
– see page 157
OR s
– see page 159
XOR s
– see page 161
CP s
– see page 163
INC r
– see page 165
INC (HL)
– see page 167
INC (IX+d)
– see page 168
INC (IY+d)
– see page 169
DEC m
– see page 170
UM008011-0816 Z80 Instruction Description
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ADD A, r
Operation
A ← A + r
Op Code
ADD
Operands
A, r
Description
The contents of register r are added to the contents of the Accumulator, and the result is
stored in the Accumulator. The r symbol identifies the registers A, B, C, D, E, H, or L,
assembled as follows in the object code:
Condition Bits Affected
S is set if result is negative; otherwise, it is reset.
Z is set if result is 0; otherwise, it is reset.
H is set if carry from bit 3; otherwise, it is reset.
Register r
A111
B000
C001
D010
E011
H100
L101
M Cycles T States 4 MHz E.T.
141.00
10 0 r00
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P/V is set if overflow; otherwise, it is reset.
N is reset.
C is set if carry from bit 7; otherwise, it is reset.
Example
If the Accumulator contains 44h and Register C contains 11h, then upon the execution of
an ADD A, C instruction, the Accumulator contains
55h.
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147
ADD A, n
Operation
A ← A + n
Op Code
ADD
Operands
A, n
Description
The n integer is added to the contents of the Accumulator, and the results are stored in the
Accumulator.
Condition Bits Affected
S is set if result is negative; otherwise, it is reset.
Z is set if result is 0; otherwise, it is reset.
H is set if carry from bit 3; otherwise, it is reset.
P/V is set if overflow; otherwise, it is reset.
N is reset.
C is set if carry from bit 7; otherwise, it is reset.
Example
If the Accumulator contains 23h, then upon the execution of an ADD A, 33h instruction,
the Accumulator contains
56h.
M Cycles T States 4 MHz E.T.
2 7 (4, 3) 1.75
n
11 0 10100
C6
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ADD A, (HL)
Operation
A ← A + (HL)
Op Code
ADD
Operands
A, (HL)
Description
The byte at the memory address specified by the contents of the HL register pair is added
to the contents of the Accumulator, and the result is stored in the Accumulator.
Condition Bits Affected
S is set if result is negative; otherwise, it is reset.
Z is set if result is 0; otherwise, it is reset.
H is set if carry from bit 3; otherwise, it is reset.
P/V is set if overflow; otherwise, it is reset.
N is reset.
C is set if carry from bit 7; otherwise, it is reset.
Example
If the Accumulator contains A0h, register pair HL contains 2323h, and memory location
2323h contains byte 08h, then upon the execution of an ADD A, (HL) instruction, the
Accumulator contains
A8h.
M Cycles T States 4 MHz E.T.
2 7 (4, 3) 1.75
10 0 10100
86
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149
ADD A, (IX + d)
Operation
A ← A + (IX+d)
Op Code
ADD
Operands
A, (IX + d)
Description
The contents of the Index (register pair IX) Register is added to a two’s complement dis-
placement d to point to an address in memory. The contents of this address is then added to
the contents of the Accumulator and the result is stored in the Accumulator.
Condition Bits Affected
S is set if result is negative; otherwise, it is reset.
Z is set if result is 0; otherwise, it is reset.
H is set if carry from bit 3; otherwise, it is reset.
P/V is set if overflow; otherwise, it is reset.
N is reset.
C is set if carry from bit 7; otherwise, it is reset.
Example
If the Accumulator contains 11h, Index Register IX contains 1000h, and memory location
1005h contains 22h, then upon the execution of an ADD A, (IX + 5h) instruction, the
Accumulator contains
33h.
M Cycles T States 4 MHz E.T.
5 19 (4, 4, 3, 5, 3) 4.75
11 1 01101
DD
10 0 10100
86
d
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ADD A, (IY + d)
Operation
A ← A + (IY+d)
Op Code
ADD
Operands
A, (IY + d)
Description
The contents of the Index (register pair IY) Register is added to a two’s complement dis-
placement d to point to an address in memory. The contents of this address is then added to
the contents of the Accumulator, and the result is stored in the Accumulator.
Condition Bits Affected
S is set if result is negative; otherwise, it is reset.
Z is set if result is 0; otherwise, it is reset.
H is set if carry from bit 3: otherwise, it is reset.
P/V is set if overflow; otherwise, it is reset.
N is reset.
C is set if carry from bit 7; otherwise, it is reset.
Example
If the Accumulator contains 11h, Index Register IY contains 1000h, and memory location
1005h contains 22h, then upon the execution of an ADD A, (IY + 5h) instruction, the
Accumulator contains
33h.
M Cycles T States 4 MHz E.T.
5 19(4, 4, 3, 5, 3) 4.75
11 1 01111
FD
10 0 10100
86
d
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ADC A, s
Operation
A ← A + s + CY
Op Code
ADC
Operands
A, s
This s operand is any of r, n, (HL), (IX+d), or (lY+d) as defined for the analogous ADD
instruction. These possible op code/operand combinations are assembled as follows in the
object code:
10 001
r*
11 0 10101
CE
n
10 0 10101
8E
11 1 10101
DD
10 0 10101
8E
d
11 1 01111
FD
10 0 10101
8E
d
ADC A,r
ADC A,n
ADC A, (HL)
ADC A, (IX+d)
ADC A, (IY+d)
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r identifies registers B, C, D, E, H, L, or A, assembled as follows in the object code field:
Description
The s operand, along with the Carry Flag (C in the F Register) is added to the contents of
the Accumulator, and the result is stored in the Accumulator.
Condition Bits Affected
S is set if result is negative; otherwise, it is reset.
Z is set if result is 0; otherwise, it is reset.
H is set if carry from bit 3; otherwise, it is reset.
P/V is set if overflow; otherwise, it is reset.
N is reset.
C is set if carry from bit 7: otherwise, it is reset.
Example
If the Accumulator contents are 16h, the Carry Flag is set, the HL register pair contains
6666h, and address 6666h contains 10h, then upon the execution of an ADC A, (HL)
instruction, the Accumulator contains
27h.
Register r
B 000
C 001
D 010
E 011
H 100
L 101
A 111
Instruction M Cycle T States 4 MHz E.T.
ADC A, r 1 4 1.00
ADC A, n 2 7 (4, 3) 1.75
ADC A, (HL) 2 7 (4, 3) 1.75
ADC A, (IX+d) 5 19 (4, 4, 3, 5, 3) 4.75
ADC A, (lY+d) 5 19 (4, 4, 3, 5, 3) 4.75
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SUB s
Operation
A ← A – s
Op Code
SUB
Operand
s
This s operand is any of r, n, (HL), (IX+d), or (lY+d) as defined for the analogous ADD
instruction. These possible op code/operand combinations are assembled as follows in the
object code:
10 100
r*
11 1 10100
D6
n
10 1 10100
96
11 1 01101
DD
10 1 10100
96
d
11 1 01111
FD
10 1 10100
96
d
SUB r
SUB n
SUB (HL)
SUB (IX+d)
SUB (IY+d)
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r identifies registers B, C, D, E, H, L, or A assembled as follows in the object code field:
Description
The s operand is subtracted from the contents of the Accumulator, and the result is stored
in the Accumulator.
Condition Bits Affected
S is set if result is negative; otherwise, it is reset.
Z is set if result is 0; otherwise, it is reset.
H is set if borrow from bit 4; otherwise, it is reset.
P/V is set if overflow; otherwise, it is reset.
N is set.
C is set if borrow; otherwise, it is reset.
Example
If the Accumulator contents are 29h, and the D Register contains 11h, then upon the exe-
cution of a SUB D instruction, the Accumulator contains
18h.
Register r
B 000
C 001
D 010
E 011
H 100
L 101
A 111
Instruction M Cycle T States 4 MHz E.T.
SUB r 1 4 1.00
SUB n 2 7 (4, 3) 1.75
SUB (HL) 2 7 (4, 3) 1.75
SUB (IX+d) 5 19 (4, 4, 3, 5, 3) 4.75
SUB (lY+d) 5 19 (4, 4, 3, 5, 3) 4.75
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155
SBC A, s
Operation
A ← A – s – CY
Op Code
SBC
Operands
A, s
The s operand is any of r, n, (HL), (IX+d), or (lY+d) as defined for the analogous ADD
instructions. These possible op code/operand combinations are assembled as follows in
the object code.
10 101
r*
11 1 10101
DE
n
10 1 10101
9E
11 1 01101
DD
10 1 10101
9E
d
11 1 01111
FD
10 1 10101
9E
d
SBC A, r
SBC A, n
SBC A, (HL)
SBC A, (IX+d)
SBC A, (IY+d)
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r identifies registers B, C, D, E, H, L, or A assembled as follows in the object code field:
Description
The s operand, along with the Carry flag (C in the F Register) is subtracted from the con-
tents of the Accumulator, and the result is stored in the Accumulator.
Condition Bits Affected
S is set if result is negative; otherwise, it is reset.
Z is set if result is 0; otherwise, it is reset.
H is set if borrow from bit 4; otherwise, it is reset.
P/V is reset if overflow; otherwise, it is reset.
N is set.
C is set if borrow; otherwise, it is reset.
Example
If the Accumulator contains 16h, the carry flag is set, the HL register pair contains 3433h,
and address
3433h contains 05h, then upon the execution of an SBC A, (HL) instruction,
the Accumulator contains
10h.
Register r
B000
C001
D010
E011
H100
L101
A111
Instruction M Cycles T States 4 MHz E.T.
SBC A, r 1 4 1.00
SBC A, n 2 7(4, 3) 1.75
SBC A, (HL) 2 7 (4, 3) 1.75
SBC A, (IX+d) 5 19 (4, 4, 3, 5, 3) 4.75
SBC A, (lY+d) 5 19 (4, 4, 3, 5, 3) 4.75
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157
AND s
Operation
A ← A ˄ s
Op Code
AND
Operand
s
The s operand is any of r, n, (HL), (IX+d), or (lY+d), as defined for the analogous ADD
instructions. These possible op code/operand combinations are assembled as follows in
the object code:
10 010
r*
11 0 10110
E6
10 0 10110
A6
11 1 01101
DD
10 0 10110
A6
11 1 01111
FD
10 0 10110
A6
AND r*
AND n
AND (HL)
AND (IX+d)
AND (IY+d)
nn
d
d
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r identifies registers B, C, D, E, H, L, or A specified in the assembled object code field, as
follows:
Description
A logical AND operation is performed between the byte specified by the s operand and the
byte contained in the Accumulator; the result is stored in the Accumulator.
Condition Bits Affected
S is set if result is negative; otherwise, it is reset.
Z is set if result is 0; otherwise, it is reset.
H is set.
P/V is reset if overflow; otherwise, it is reset.
N is reset.
C is reset.
Example
If Register B contains 7Bh (0111 1011) and the Accumulator contains C3h (1100 0011),
then upon the execution of an AND B instruction, the Accumulator contains
43h (0100
0011).
Register r
B 000
C 001
D 010
E 011
H 100
L 101
A 111
Instruction M Cycles T States 4 MHz E.T.
AND r 1 4 1.00
AND n 2 7 (4, 3) 1.75
AND (HL) 2 7 (4, 3) 1.75
AND (IX+d) 5 19 (4, 4, 3, 5, 3) 4.75
AND (IX+d) 5 19 (4, 4, 3. 5, 3) 4.75
UM008011-0816 Z80 Instruction Description
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159
OR s
Operation
A ← A ˅ s
Op Code
OR
Operand
s
The s operand is any of r, n, (HL), (IX+d), or (lY+d), as defined for the analogous ADD
instructions. These possible op code/operand combinations are assembled as follows in
the object code:
10 110
r*
11 1 10110
F6
10 1 10110
B6
11 1 01101
DD
10 1 10110
B6
11 1 01111
FD
10 1 10110
B6
OR r*
OR n
OR (HL)
OR (IX+d)
OR (IY+d)
n
d
d
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r identifies registers B, C–, D, E, H, L, or A specified in the assembled object code field,
as follows:
Description
A logical OR operation is performed between the byte specified by the s operand and the
byte contained in the Accumulator; the result is stored in the Accumulator.
Condition Bits Affected
S is set if result is negative; otherwise, it is reset.
Z is set if result is 0; otherwise, it is reset.
H is reset.
P/V is set if overflow; otherwise, it is reset.
N is reset.
C is reset.
Example
If the H Register contains 48h (0100 0100), and the Accumulator contains 12h (0001
0010), then upon the execution of an OR H instruction, the Accumulator contains 5Ah
(
0101 1010).
Register r
B 000
C 001
D 010
E 011
H 100
L 101
A 111
Instruction M Cycles T States 4 MHz E.T.
OR r 1 4 1.00
OR n 2 7 (4, 3) 1.75
OR (HL) 2 7 (4, 3) 1.75
OR (IX+d) 5 19 (4, 4, 3, 5, 3) 4.75
OR (lY+d) 5 19 (4, 4, 3, 5, 3) 4.75
UM008011-0816 Z80 Instruction Description
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161
XOR s
Operation
A ← A ⊕ s
Op Code
XOR
Operand
s
The s operand is any of r, n, (HL), (IX+d), or (lY+d), as defined for the analogous ADD
instructions. These possible Op Code/operand combinations are assembled as follows in
the object code:
10 011
r*
11 0 10111
EE
10 0 10111
AE
11 1 01101
DD
10 0 10111
AE
11 1 01111
FD
10 0 10111
AE
XOR r*
XOR n
XOR (HL)
XOR (IX+d)
XOR (IY+d)
n
d
d
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r identifies registers B, C, D, E, H, L, or A specified in the assembled object code field, as
follows:
Description
The logical exclusive-OR operation is performed between the byte specified by the s oper-
and and the byte contained in the Accumulator; the result is stored in the Accumulator.
Condition Bits Affected
S is set if result is negative; otherwise, it is reset.
Z is set if result is 0; otherwise, it is reset.
H is reset.
P/V is set if parity even; otherwise, it is reset.
N is reset.
C is reset.
Example
If the Accumulator contains 96h (1001 0110), then upon the execution of an XOR 5Dh
(5Dh = 0101 1101) instruction, the Accumulator contains CBh (1100 1011).
Register r
B 000
C 001
D 010
E 011
H 100
L 101
A 1l1
Instruction M Cycles T States 4 MHz E.T.
XOR r141.00
XOR n 2 7 (4, 3) 1.75
XOR (HL) 2 7 (4, 3) 1.75
XOR (IX+d) 5 19 (4, 4, 3, 5, 3) 4.75
XOR (lY+d) 5 19 (4, 4, 3, 5, 3) 4.75
UM008011-0816 Z80 Instruction Description
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163
CP s
Operation
A – s
Op Code
CP
Operand
s
The s operand is any of r, n, (HL), (IX+d), or (lY+d), as defined for the analogous ADD
instructions. These possible op code/operand combinations are assembled as follows in
the object code:
10 111
r*
11 1 10111
FE
10 1 10111
BE
11 1 01101
DD
10 1 10111
BE
11 1 01111
FD
10 1 10111
BE
CP r*
CP n
CP (HL)
CP (IX+d)
CP (IY+d)
n
d
d
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r identifies registers B, C, D, E, H, L, or A specified in the assembled object code field, as
follows:
Description
The contents of the s operand are compared with the contents of the Accumulator. If there
is a true compare, the Z flag is set. The execution of this instruction does not affect the
contents of the Accumulator.
Condition Bits Affected
S is set if result is negative; otherwise, it is reset.
Z is set if result is 0; otherwise, it is reset.
H is set if borrow from bit 4; otherwise, it is reset.
P/V is set if overflow; otherwise, it is reset.
N is set.
C is set if borrow; otherwise, it is reset.
Example
If the Accumulator contains 63h, the HL register pair contains 6000h, and memory loca-
tion
6000h contains 60h, the instruction CP (HL) results in the PN flag in the F Register
resetting.
Register r
B 000
C 001
D 010
E 011
H 100
L 101
A 111
Instruction M Cycles T States 4 MHz E.T.
CP r 1 4 1.00
CP n 2 7(4, 3) 1.75
CP (HL) 2 7 (4, 3) 1.75
CP (IX+d) 5 19 (4, 4, 3, 5, 3) 4.75
CP (lY+d) 5 19 (4, 4, 3, 5, 3) 4.75
UM008011-0816 Z80 Instruction Description
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165
INC r
Operation
r ← r + 1
Op Code
INC
Operand
r
Description
Register r is incremented and register r identifies any of the registers A, B, C, D, E, H, or
L, assembled as follows in the object code.
Condition Bits Affected
S is set if result is negative; otherwise, it is reset.
Z is set if result is 0; otherwise, it is reset.
H is set if carry from bit 3; otherwise, it is reset.
P/V is set if r was
7Fh before operation; otherwise, it is reset.
Register r
A 111
B 000
C 001
D 010
E 011
H 100
L 101
M Cycles T States 4 MHz E.T.
141.00
00 r 001
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N is reset.
C is not affected.
Example
If the D Register contains 28h, then upon the execution of an INC D instruction, the D
Register contains
29h.
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167
INC (HL)
Operation
(HL) ← (HL) + 1
Op Code
INC
Operand
(HL)
Description
The byte contained in the address specified by the contents of the HL register pair is incre-
mented.
Condition Bits Affected
S is set if result is negative; otherwise, it is reset.
Z is set if result is 0; otherwise, it is reset.
H is set if carry from bit 3; otherwise, it is reset.
P/V is set if (HL) was
7Fh before operation; otherwise, it is reset.
N is reset.
C is not affected.
Example
If the HL register pair contains 3434h and address 3434h contains 82h, then upon the
execution of an INC (HL) instruction, memory location
3434h contains 83h.
M Cycles T States 4 MHz E.T.
3 11 (4, 4, 3) 2.75
00 1 00110
34
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INC (IX+d)
Operation
(IX+d) ← (IX+d) + 1
Op Code
INC
Operands
(IX+d)
Description
The contents of Index Register IX (register pair IX) are added to the two’s-complement
displacement integer, d, to point to an address in memory. The contents of this address are
then incremented.
Condition Bits Affected
S is set if result is negative; otherwise, it is reset.
Z is set if result is 0; otherwise, it is reset.
H is set if carry from bit 3; otherwise, it is reset.
P/V is set if (IX+d) was
7Fh before operation; otherwise, it is reset.
N is reset.
C is not affected.
Example
If Index Register pair IX contains 2020h and memory location 2030h contains byte 34h,
then upon the execution of an INC (IX+
10h) instruction, memory location 2030h con-
tains
35h.
M Cycles T States 4 MHz E.T.
6 23 (4, 4, 3, 5, 4, 3) 5.75
11 1 01101
DD
00 1 00110
34
d
UM008011-0816 Z80 Instruction Description
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169
INC (IY+d)
Operation
(lY+d) ← (lY+d) + 1
Op Code
INC
Operands
(lY+d)
Description
The contents of Index Register IY (register pair IY) are added to the two’s-complement
displacement integer, d, to point to an address in memory. The contents of this address are
then incremented.
Condition Bits Affected
S is set if result is negative; otherwise, it is reset.
Z is set if result is 0; otherwise, it is reset.
H is set if carry from bit 3; otherwise, it is reset.
P/V is set if (lY+d) was
7Fh before operation; otherwise, it is reset.
N is reset.
C is not affected.
Example
If Index Register IY are 2020h and memory location 2030h contains byte 34h, then upon
the execution of an INC (IY+
10h) instruction, memory location 2030h contains 35h.
M Cycles T States 4 MHz E.T.
6 23 (4, 4, 3, 5, 4, 3) 5.75
11 1 01111
FD
00 1 00110
34
d
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DEC m
Operation
m ← m – 1
Op Code
DEC
Operand
m
The m operand is any of r, (HL), (IX+d), or (lY+d), as defined for the analogous INC
instructions. These possible op code/operand combinations are assembled as follows in
the object code:
r identifies registers B, C, D, E, H, L, or A assembled as follows in the object code field:
Register r
B 000
C 001
D 010
E 011
H 100
L 101
A 111
00 r 011
00 1 01110
35
11 1 01101
DD
00 1 01110
35
11 1 01111
FD
00 1 01110
35
DEC (HL)
DEC (IX+d)
DEC (IY+d)
d
d
DEC r*
UM008011-0816 Z80 Instruction Description
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Description
The byte specified by the m operand is decremented.
Condition Bits Affected
S is set if result is negative; otherwise, it is reset.
Z is set if result is 0; otherwise, it is reset.
H is set if borrow from bit 4, otherwise, it is reset.
P/V is set if m was
80h before operation; otherwise, it is reset.
N is set.
C is not affected.
Example
If the D Register contains byte 2Ah, then upon the execution of a DEC D instruction, the D
Register contains
29h.
Instruction M Cycles T States 4 MHz E.T.
DEC r 1 4 1.00
DEC (HL) 3 11 (4, 4, 3) 2.75
DEC (IX+d) 6 23 (4, 4, 3, 5, 4, 3) 5.75
DEC (lY+d) 6 23 (4, 4, 3, 5, 4, 3) 5.75
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General-Purpose Arithmetic and CPU
Control Groups
The following general-purpose arithmetic and CPU control group instructions are each
described in this section. Simply click to jump to an instruction’s description to learn
more.
DAA
– see page 173
CPL
– see page 175
NEG
– see page 176
CCF
– see page 178
SCF
– see page 179
NOP
– see page 180
HALT
– see page 181
DI
– see page 182
EI
– see page 183
IM 0
– see page 184
IM 1
– see page 185
IM 2
– see page 186
UM008011-0816 Z80 Instruction Description
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173
DAA
Operation
@
Op Code
DAA
Operands
None.
Description
This instruction conditionally adjusts the Accumulator for BCD addition and subtraction
operations. For addition (ADD, ADC, INC) or subtraction (SUB, SBC, DEC, NEG), the
following table indicates the operation being performed:
Operation
C Before
DAA
Hex Value
In Upper
Digit
(Bits 7–4)
H Before
DAA
Hex Value
In Lower
Digit
(Bits 3–0)
Number
Added To
Byte
C After
DAA
09–000–900 0
0 0–8 0 A–F 06 0
00–910–306 0
ADD 0 A–F 0 0–9 60 1
ADC 0 9–F 0 A–F 66 1
INC 0 A–F 1 0–3 66 1
10–200–960 1
1 0–2 0 A–F 66 1
10–310–366 1
SUB 0 0–9 0 0–9 00 0
SBC 0 0–8 1 6–F FA 0
DEC 1 7–F 0 0–9 A0 1
NEG 1 6–7 1 6–F 9A 1
00 0 11110
27
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Condition Bits Affected
S is set if most-significant bit of the Accumulator is 1 after an operation; otherwise, it is
reset.
Z is set if the Accumulator is 0 after an operation; otherwise, it is reset.
H: see the DAA instruction table on the previous page.
P/V is set if the Accumulator is at even parity after an operation; otherwise, it is reset.
N is not affected.
C: see the DAA instruction table on the previous page.
Example
An addition operation is performed between 15 (BCD) and 27 (BCD); simple decimal
arithmetic provides the following result:
15
+
27
42
The binary representations are added in the Accumulator according to standard binary
arithmetic, as follows:
0001 0101
+ 0010
0111
0011 1100 = 3C
The sum is ambiguous. The DAA instruction adjusts this result so that the correct BCD
representation is obtained, as follows:
0011 1100
+ 0000
0110
0100 0010 = 42
M Cycles T States 4 MHz E.T.
141.00
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CPL
Operation
A ← A
Op Code
CPL
Operands
None.
Description
The contents of the Accumulator (Register A) are inverted (one’s complement).
Condition Bits Affected
S is not affected.
Z is not affected.
H is set.
P/V is not affected.
N is set.
C is not affected.
Example
If the Accumulator contains 1011 0100, then upon the execution of a CPL instruction, the
Accumulator contains
0100 1011.
M Cycles T States 4 MHz E.T.
141.00
00 0 11111
2F
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NEG
Operation
A ← 0 – A
Op Code
NEG
Operands
None.
Description
The contents of the Accumulator are negated (two’s complement). This method is the
same as subtracting the contents of the Accumulator from zero.
The 80h address remains unchanged.
Condition Bits Affected
S is set if result is negative; otherwise, it is reset.
Z is set if result is 0; otherwise, it is reset.
H is set if borrow from bit 4; otherwise, it is reset.
P/V is set if Accumulator was
80h before operation; otherwise, it is reset.
N is set.
C is set if Accumulator was not
00h before operation; otherwise, it is reset.
M Cycles T States 4 MHz E.T.
2 8 (4, 4) 2.00
11 0 01111
ED
01 0 00100
44
Note:
UM008011-0816 Z80 Instruction Description
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Example
The Accumulator contains the following data:
Upon the execution of a NEG instruction, the Accumulator contains:
10 1 00001
01 0 00011
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CCF
Operation
CY ← CY
Op Code
CCF
Operands
None.
Description
The Carry flag in the F Register is inverted.
Condition Bits Affected
S is not affected.
Z is not affected.
H, previous carry is copied.
P/V is not affected.
N is reset.
C is set if CY was 0 before operation; otherwise, it is reset.
M Cycles T States 4 MHz E.T.
141.00
00 1 11111
3F
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SCF
Operation
CY ← 1
Op Code
SCF
Operands
None.
Description
The Carry flag in the F Register is set.
Condition Bits Affected
S is not affected.
Z is not affected.
H is reset.
P/V is not affected.
N is reset.
C is set.
M Cycles T States 4 MHz E.T.
141.00
00 1 11110
37
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NOP
Operation
—
Op Code
NOP
Operands
None.
Description
The CPU performs no operation during this machine cycle.
Condition Bits Affected
None.
M Cycles T States 4 MHz E.T.
141.00
00 0 00000
00
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HALT
Operation
—
Op Code
HALT
Operands
None.
Description
The HALT instruction suspends CPU operation until a subsequent interrupt or reset is
received. While in the HALT state, the processor executes NOPs to maintain memory
refresh logic.
Condition Bits Affected
None.
M Cycles T States 4 MHz E.T.
141.00
01 1 10110
76
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DI
Operation
IFF ← 0
Op Code
DI
Operands
None.
Description
DI disables the maskable interrupt by resetting the interrupt enable flip-flops (IFF1 and
IFF2).
This instruction disables the maskable interrupt during its execution.
Condition Bits Affected
None.
Example
When the CPU executes the instruction DI the maskable interrupt is disabled until it is
subsequently re-enabled by an EI instruction. The CPU does not respond to an Interrupt
Request (INT) signal.
M Cycles T States 4 MHz E.T.
141.00
11 1 11010
F3
Note:
UM008011-0816 Z80 Instruction Description
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EI
Operation
IFF ← 1
Op Code
EI
Operands
None.
Description
The enable interrupt instruction sets both interrupt enable flip flops (IFFI and IFF2) to a
logic 1, allowing recognition of any maskable interrupt.
During the execution of this instruction and the following instruction, maskable interrupts
are disabled.
Condition Bits Affected
None.
Example
When the CPU executes an EI RETI instruction, the maskable interrupt is enabled then
upon the execution of an the RETI instruction.
M Cycles T States 4 MHz E.T.
141.00
11 1 11011
FB
Note:
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IM 0
Operation
Set Interrupt Mode 0
Op Code
IM
Operand
0
Description
The IM 0 instruction sets Interrupt Mode 0. In this mode, the interrupting device can insert
any instruction on the data bus for execution by the CPU. The first byte of a multi-byte
instruction is read during the interrupt acknowledge cycle. Subsequent bytes are read in by
a normal memory read sequence.
Condition Bits Affected
None.
M Cycles T States 4 MHz E.T.
2 8 (4, 4) 2.00
11 0 01111
ED
01 0 10100
46
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IM 1
Operation
Set Interrupt Mode 1
Op Code
IM
Operand
1
Description
The IM 1 instruction sets Interrupt Mode 1. In this mode, the processor responds to an
interrupt by executing a restart at address
0038h.
Condition Bits Affected
None.
M Cycles T States 4 MHz E.T.
2 8 (4, 4) 2.00
11 0 01111
ED
01 1 10100
56
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IM 2
Operation
Set Interrupt Mode 2
Op Code
IM
Operand
2
Description
The IM 2 instruction sets the vectored Interrupt Mode 2. This mode allows an indirect call
to any memory location by an 8-bit vector supplied from the peripheral device. This vector
then becomes the least-significant eight bits of the indirect pointer, while the I Register in
the CPU provides the most-significant eight bits. This address points to an address in a
vector table that is the starting address for the interrupt service routine.
Condition Bits Affected
None.
M Cycles T States 4 MHz E.T.
2 8 (4, 4) 2.00
11 0 01111
ED
01 1 10101
5E
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16-Bit Arithmetic Group
The following 16-bit arithmetic group instructions are each described in this section. Sim-
ply click to jump to an instruction’s description to learn more.
ADD HL, ss
– see page 188
ADC HL, ss
– see page 190
SBC HL, ss
– see page 192
ADD IX, pp
– see page 194
ADD IY, rr
– see page 196
INC ss
– see page 198
INC IX
– see page 199
INC IY
– see page 200
DEC ss
– see page 201
DEC IX
– see page 202
DEC IY
– see page 203
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ADD HL, ss
Operation
HL ← HL + ss
Op Code
ADD
Operands
HL, ss
Description
The contents of register pair ss (any of register pairs BC, DE, HL, or SP) are added to the
contents of register pair HL and the result is stored in HL. In the assembled object code,
operand ss is specified as follows:
Condition Bits Affected
S is not affected.
Z is not affected.
H is set if carry from bit 11; otherwise, it is reset.
P/V is not affected.
N is reset.
Register
Pair ss
BC 00
DE 01
HL 10
SP 11
M Cycles T States 4 MHz E.T.
3 11 (4, 4, 3) 2.75
00 s 010s1
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C is set if carry from bit 15; otherwise, it is reset.
Example
If register pair HL contains the integer 4242h and register pair DE contains 1111h, then
upon the execution of an ADD HL, DE instruction, the HL register pair contains
5353h.
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ADC HL, ss
Operation
HL ← HL + ss + CY
Op Code
ADC
Operands
HL, ss
Description
The contents of register pair ss (any of register pairs BC, DE, HL, or SP) are added with
the Carry flag (C flag in the F Register) to the contents of register pair HL, and the result is
stored in HL. In the assembled object code, operand ss is specified as follows:
Condition Bits Affected
S is set if result is negative; otherwise, it is reset.
Z is set if result is 0; otherwise, it is reset.
H is set if carry from bit 11; otherwise, it is reset.
P/V is set if overflow; otherwise, it is reset.
Register
Pair ss
BC
00
DE
01
HL
10
SP
11
M Cycles T States 4 MHz E.T.
4 15 (4, 4, 4, 3) 3.75
11 0 01111
ED
01 s 100s1
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191
N is reset.
C is set if carry from bit 15; otherwise, it is reset.
Example
If register pair BC contains 2222h, register pair HL contains 5437h, and the Carry Flag is
set, then upon the execution of an ADC HL, BC instruction, HL contains
765Ah.
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SBC HL, ss
Operation
HL ← HL – ss – CY
Op Code
SBC
Operands
HL, ss
Description
The contents of the register pair ss (any of register pairs BC, DE, HL, or SP) and the Carry
Flag (C flag in the F Register) are subtracted from the contents of register pair HL, and the
result is stored in HL. In the assembled object code, operand ss is specified as follows:
Condition Bits Affected
S is set if result is negative; otherwise, it is reset.
Z is set if result is 0; otherwise, it is reset.
H is set if borrow from bit 12; otherwise, it is reset.
P/V is set if overflow; otherwise, it is reset.
Register
Pair ss
BC
00
DE
01
HL
10
SP
11
M Cycles T States 4 MHz E.T.
4 15 (4, 4, 4, 3) 3.75
11 0 01111
ED
01 s 100s0
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193
N is set.
C is set if borrow; otherwise, it is reset.
Example
If the HL register pair contains 9999h, register pair DE contains 1111h, and the Carry
flag is set, then upon the execution of a
n SBC HL, DE instruction, HL contains 8887h.
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ADD IX, pp
Operation
IX ← IX + pp
Op Code
ADD
Operands
IX, pp
Description
The contents of register pair pp (any of register pairs BC, DE, IX, or SP) are added to the
contents of Index Register IX, and the results are stored in IX. In the assembled object
code, operand pp is specified as follows:
Condition Bits Affected
S is not affected.
Z is not affected.
H is set if carry from bit 11; otherwise, it is reset.
P/V is not affected.
Register
Pair ss
BC
00
DE
01
IX
10
SP
11
M Cycles T States 4 MHz E.T.
4 15 (4, 4, 4, 3) 3.75
11 1 01101
DD
00 p 010p1
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N is reset.
C is set if carry from bit 15; otherwise, it is reset.
Example
If Index Register IX contains 333h and register pair BC contains 5555h, then upon the
execution of an ADD IX, BC instruction, IX contains
8888h.
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ADD IY, rr
Operation
IY ← IY + rr
Op Code
ADD
Operands
IY, rr
Description
The contents of register pair rr (any of register pairs BC, DE, IY, or SP) are added to the
contents of Index Register IY, and the result is stored in IY. In the assembled object code,
the rr operand is specified as follows:
Condition Bits Affected
S is not affected.
Z is not affected.
H is set if carry from bit 11; otherwise, it is reset.
P/V is not affected.
Register
Pair ss
BC
00
DE
01
IY
10
SP
11
M Cycles T States 4 MHz E.T.
4 15 (4, 4, 4, 3) 3.75
11 1 01111
FD
00 r 010r1
UM008011-0816 Z80 Instruction Description
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N is reset.
C is set if carry from bit 15; otherwise, it is reset.
Example
If Index Register IY contains 333h and register pair BC contains 555h, then upon the exe-
cution of an ADD IY, BC instruction, IY contains
8888h.
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INC ss
Operation
ss ← ss + 1
Op Code
INC
Operand
ss
Description
The contents of register pair ss (any of register pairs BC, DE, HL, or SP) are incremented.
In the assembled object code, operand ss is specified as follows:
Condition Bits Affected
None.
Example
If the register pair contains 1000h, then upon the execution of an INC HL instruction, HL
contains
1001h.
Register
Pair ss
BC
00
DE
01
HL
10
SP
11
M Cycles T States 4 MHz E.T.
161.50
00 s 110s0
UM008011-0816 Z80 Instruction Description
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199
INC IX
Operation
IX ← IX + 1
Op Code
INC
Operand
IX
Description
The contents of Index Register IX are incremented.
Condition Bits Affected
None.
Example
If Index Register IX contains the integer 3300h, then upon the execution of an INC IX
instruction, Index Register IX contains
3301h.
M Cycles T States 4 MHz E.T.
2 10 (4, 6) 2.50
11 1 01101
DD
00 0 11010
23
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INC IY
Operation
IY ← IY + 1
Op Code
INC
Operand
IY
Description
The contents of Index Register IY are incremented.
Condition Bits Affected
None.
Example
If the index register contains 2977h, then upon the execution of an INC IY instruction,
Index Register IY contains
2978h.
M Cycles T States 4 MHz E.T.
2 10 (4, 6) 2.50
11 1 01111
FD
00 0 11010
23
UM008011-0816 Z80 Instruction Description
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DEC ss
Operation
ss ← ss – 1
Op Code
DEC
Operand
ss
Description
The contents of register pair ss (any of the register pairs BC, DE, HL, or SP) are decre-
mented. In the assembled object code, operand ss is specified as follows:
Condition Bits Affected
None.
Example
If register pair HL contains 1001h, then upon the execution of an DEC HL instruction, HL
contains
1000h.
Register
Pair ss
BC
00
DE
01
HL
10
SP
11
M Cycles T States 4 MHz E.T.
161.50
00 s 110s1
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DEC IX
Operation
IX ← IX – 1
Op Code
DEC
Operand
IX
Description
The contents of Index Register IX are decremented.
Condition Bits Affected
None.
Example
If Index Register IX contains 2006h, then upon the execution of a DEC IX instruction,
Index Register IX contains
2005h.
M Cycles T States 4 MHz E.T.
2 10 (4, 6) 2.50
11 1 01101
DD
00 0 11011
2B
UM008011-0816 Z80 Instruction Description
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DEC IY
Operation
IY ← IY– 1
Op Code
DEC
Operand
IY
Description
The contents of Index Register IY are decremented.
Condition Bits Affected
None.
Example
If Index Register IY contains 7649h, then upon the execution of a DEC IY instruction,
Index Register IY contains
7648h.
M Cycles T States 4 MHz E.T.
2 10 (4, 6) 2.50
11 1 01111
FD
00 0 11011
2B
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Rotate and Shift Group
The following rotate and shift group instructions are each described in this section. Simply
click to jump to an instruction’s description to learn more.
RLCA
– see page 205
RLA
– see page 207
RRCA
– see page 209
RRA
– see page 211
RLC r
– see page 213
RLC (HL)
– see page 215
RLC (IX+d)
– see page 217
RLC (IY+d)
– see page 219
RL m
– see page 221
RRC m
– see page 224
RR m
– see page 227
SLA m
– see page 230
SRA m
– see page 233
SRL m
– see page 236
RLD
– see page 238
RRD
– see page 240
UM008011-0816 Z80 Instruction Description
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205
RLCA
Operation
Op Code
RLCA
Operands
None.
Description
The contents of the Accumulator (Register A) are rotated left 1 bit position. The sign bit
(bit 7) is copied to the Carry flag and also to bit 0. Bit 0 is the least-significant bit.
Condition Bits Affected
S is not affected.
Z is not affected.
H is reset.
P/V is not affected.
N is reset.
C is data from bit 7 of Accumulator.
M Cycles T States 4 MHz E.T.
141.00
CY
70
A
00 0 11100
07
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Example
The Accumulator contains the following data:
Upon the execution of an RLCA instruction, the Accumulator and Carry flag contains:
10 0 00001
76 4 10253
00 1 01000
76 4 10253
C
1
UM008011-0816 Z80 Instruction Description
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RLA
Operation
Op Code
RLA
Operands
None.
Description
The contents of the Accumulator (Register A) are rotated left 1 bit position through the
Carry flag. The previous contents of the Carry flag are copied to bit 0. Bit 0 is the least-
significant bit.
Condition Bits Affected
Condition Bits Affected.
S is not affected.
Z is not affected.
H is reset.
P/V is not affected.
N is reset.
C is data from bit 7 of Accumulator.
M Cycles T States 4 MHz E.T.
141.00
00 1 11100
17
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Example
The Accumulator and the Carry flag contains the following data:
Upon the execution of an RLA instruction, the Accumulator and the Carry flag contains:
01 1 10110
76 4 10253
C
1
11 0 01111
76 4 10253
C
0
UM008011-0816 Z80 Instruction Description
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209
RRCA
Operation
Op Code
RRCA
Operands
None.
Description
The contents of the Accumulator (Register A) are rotated right 1 bit position. Bit 0 is cop-
ied to the Carry flag and also to bit 7. Bit 0 is the least-significant bit.
Condition Bits Affected
S is not affected.
Z is not affected.
H is reset.
P/V is not affected.
N is reset.
C is data from bit 0 of Accumulator.
Example
The Accumulator contains the following data.
M Cycles T States 4 MHz E.T.
141.00
CY
07
A
00 0 11101
0F
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Upon the execution of an RRCA instruction, the Accumulator and the Carry flag now con-
tain:
00 0 010
64 10253
7
0
1
00 1 010
64 10253
7
1
0
1
C
UM008011-0816 Z80 Instruction Description
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211
RRA
Operation
Op Code
RRA
Operands
None.
Description
The contents of the Accumulator (Register A) are rotated right 1 bit position through the
Carry flag. The previous contents of the Carry flag are copied to bit 7. Bit 0 is the least-
significant bit.
Condition Bits Affected
S is not affected.
Z is not affected.
H is reset.
P/V is not affected.
N is reset.
C is data from bit 0 of Accumulator.
M Cycles T States 4 MHz E.T.
141.00
CY
07
A
00 1 11101
1F
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Example
The Accumulator and the Carry Flag contain the following data:
Upon the execution of an RRA instruction, the Accumulator and the Carry flag now con-
tain:
100111 00
76 4 10253
C
0
000101 01
76 4 10253
C
1
UM008011-0816 Z80 Instruction Description
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RLC r
Operation
Op Code
RLC
Operand
r
Description
The contents of register r are rotated left 1 bit position. The contents of bit 7 are copied to
the Carry flag and also to bit 0. In the assembled object code, operand r is specified as fol-
lows:
Register r
B 000
C 001
D 010
E 011
H 100
L 101
A 111
M Cycles T States 4 MHz E.T.
2 8 (4, 4) 2.00
CY
70
r
00 000
r
11 0 11001
CB
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Condition Bits Affected
S is set if result is negative; otherwise, it is reset.
Z is set if result is 0; otherwise, it is reset.
H is reset.
P/V is set if parity even; otherwise, it is reset.
N is reset.
C is data from bit 7 of source register.
Example
Register r contains the following data.
Upon the execution of an RLC r instruction, register r and the Carry flag now contain:
001010 00
76 4 10253
00 1 01000
76 4 10253
C
1
UM008011-0816 Z80 Instruction Description
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215
RLC (HL)
Operation
Op Code
RLC
Operand
(HL)
Description
The contents of the memory address specified by the contents of register pair HL are
rotated left 1 bit position. The contents of bit 7 are copied to the Carry flag and also to bit
0. Bit 0 is the least-significant bit.
Condition Bits Affected
S is set if result is negative; otherwise, it is reset.
Z is set if result is 0; otherwise, it is reset.
H is reset.
P/V is set if parity even; otherwise, it is reset.
N is reset.
C is data from bit 7 of source register.
M Cycles T States 4 MHz E.T.
4 15 (4, 4, 4, 3) 3.75
CY
70
(HL)
11 0 11001
CB
00 0 10100
06
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Example
The HL register pair contains 2828h and the contents of memory location 2828h are:
Upon the execution of an RLC(HL) instruction, memory location
2828h and the Carry
flag now contain:
10 0 00001
76 4 10253
00 1 01000
76 4 10253
C
1
UM008011-0816 Z80 Instruction Description
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217
RLC (IX+d)
Operation
Op Code
RLC
Operand
(IX+d)
Description
The contents of the memory address specified by the sum of the contents of Index Register
IX and the two’s-complement displacement integer, d, are rotated left 1 bit position. The
contents of bit 7 are copied to the Carry flag and also to bit 0. Bit 0 is the least-significant
bit.
Condition Bits Affected
S is set if result is negative; otherwise, it is reset.
Z is set if result is 0; otherwise, it is reset.
H is reset.
P/V is set if parity even; otherwise, it is reset.
N is reset.
M Cycles T States 4 MHz E.T.
6 23 (4, 4, 3, 5, 4, 3) 5.75
CY
70
(IX+d)
11 1 01101
DD
11 0 11001
CB
00 0 10100
06
d
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C is data from bit 7 of source register.
Example
Index Register IX contains 1000h and memory location 1022h contains the following
data.
Upon the execution of an RLC (IX+
2h) instruction, memory location 1002h and the
Carry flag now contain:
10 0 00001
76 4 10253
00 1 01000
76 4 10253
C
1
UM008011-0816 Z80 Instruction Description
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219
RLC (IY+d)
Operation
Op Code
RLC
Operand
(lY+d)
Description
The contents of the memory address specified by the sum of the contents of Index Register
IY and the two’s-complement displacement integer, d, are rotated left 1 bit position. The
contents of bit 7 are copied to the Carry flag and also to bit 0. Bit 0 is the least-significant
bit.
Condition Bits Affected
S is set if result is negative; otherwise, it is reset.
Z is set if result is 0; otherwise, it is reset.
H is reset.
P/V is set if parity even; otherwise, it is reset.
N is reset.
M Cycles T States 4 MHz E.T.
6 23 (4, 4, 3, 5, 4, 3) 5.75
CY
70
(IY+d)
11 1 01111
FD
11 0 11001
CB
00 0 10100
06
d
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C is data from bit 7 of source register.
Example
Index Register IY contains 1000h and memory location 1002h contain the following
data:
Upon the execution of an RLC (IY+
2h) instruction, memory location 1002h and the
Carry flag now contain:
10 0 00001
76 4 10253
00 1 01000
76 4 10253
C
1
UM008011-0816 Z80 Instruction Description
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221
RL m
Operation
Op Code
RL
Operand
m
The m operand is any of r, (HL), (IX+d), or (lY+d), as defined for the analogous RLC
instructions. In the assembled object code, the possible op code/operand combinations are
specified as follows:
CY
70
m
00 100
r*
11 0 11001
CB
11 0 11001
CB
11 1 01101
DD
11 0 11001
CB
11 1 01111
FD
11 0 11001
CB
RL r*
RL (HL)
RL (IX+d)
RL (IY+d)
d
d
00 1 10100
16
00 1 10100
16
00 1 10100
16
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r identifies registers B, C, D, E, H, L, or A assembled as follows in the object code field:
Description
The contents of the m operand are rotated left 1 bit position. The contents of bit 7 are cop-
ied to the Carry flag, and the previous contents of the Carry flag are copied to bit 0.
Condition Bits Affected
S is set if result is negative; otherwise, it is reset.
Z is set if result is 0; otherwise, it is reset.
H is reset.
P/V is set if parity even; otherwise, it is reset.
N is reset.
C is data from bit 7 of source register.
Example
The D Register and the Carry flag contain the following data.
Register r
B
000
C
001
D
010
E
011
H
100
L
101
A
111
Instruction M Cycles T States 4 MHz E.T.
RL r 2 8 (4, 4) 2.00
RL (HL) 4 15(4, 4, 4, 3) 3.75
RL (IX+d) 6 23 (4, 4, 3, 5, 4, 3) 5.75
RL (IY+d) 6 23 (4, 4, 3, 5, 4, 3) 5.75
10 0 11101
76 4 10253
C
0
UM008011-0816 Z80 Instruction Description
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Upon the execution of an RL D instruction, the D Register and the Carry flag now contain:
00 1 10101
76 4 10253
C
1
Z80 Instruction Set UM008011-0816
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RRC m
Operation
Op Code
RRC
Operand
m
The m operand is any of r, (HL), (IX+d), or (lY+d), as defined for the analogous RLC
instructions. In the assembled object code, the possible op code/operand combinations are
specified as follows:
UM008011-0816 Z80 Instruction Description
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r identifies registers B, C, D, E, H, L, or A assembled as follows in the object code field:
Description
The contents of the m operand are rotated right 1 bit position. The contents of bit 0 are
copied to the Carry flag and also to bit 7. Bit 0 is the least-significant bit.
Register r
B 000
C 001
D 010
E 011
H 100
L 101
A 111
00 001
r*
11 0 11001
CB
11 0 11001
CB
11 1 01101
DD
11 0 11001
CB
11 1 01111
FD
11 0 11001
CB
RRC r*
RRC (HL)
RRC (IX+d)
RRC (IY+d)
d
d
00 0 10101
OE
00 0 10101
OE
00 0 10101
OE
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Condition Bits Affected
S is set if result is negative; otherwise, it is reset.
Z is set if result is 0; otherwise, it is reset.
H is reset.
P/V is set if parity even; otherwise, it is reset.
N is reset.
C is data from bit 0 of source register.
Example
Register A contains the following data.
Upon the execution of an RRC A instruction, Register A and the Carry flag now contain:
Instruction M Cycles T States 4 MHz E.T.
RRC r 2 8 (4, 4) 2.00
RRC (HL) 4 15 (4, 4, 4, 3) 3.75
RRC (IX+d) 6 23 (4, 4, 3, 5, 4, 3) 5.75
RRC (lY+d) 6 23 (4, 4, 3, 5, 4, 3) 5.75
00 1 01010
76 4 10253
001010 01
76 4 10253
C
1
UM008011-0816 Z80 Instruction Description
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227
RR m
Operation
Op Code
RR
Operand
m
The m operand is any of r, (HL), (IX+d), or (lY+d), as defined for the analogous RLC
instructions. In the assembled object code, the possible op code/operand combinations are
specified as follows:
Z80 Instruction Set UM008011-0816
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r identifies registers B, C, D, E, H, L, or A assembled as follows in the object code field:
Description
The contents of operand m are rotated right 1 bit position through the Carry flag. The con-
tents of bit 0 are copied to the Carry flag and the previous contents of the Carry flag are
copied to bit 7. Bit 0 is the least-significant bit.
Register r
B 000
C 001
D 010
E 011
H 100
L 101
A 111
00 001
r*
11 0 11001
CB
11 0 11001
CB
11 1 01101
DD
11 0 11001
CB
11 1 01111
FD
11 0 11001
CB
RR r*
RR (HL)
RR (IX+d)
RR (IY+d)
d
d
00 1 10101
1E
00 1 10101
1E
00 1 10101
1E
UM008011-0816 Z80 Instruction Description
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Condition Bits Affected
S is set if result is negative; otherwise, it is reset.
Z is set if result is 0; otherwise, it is reset.
H is reset.
P/V is set if parity even; otherwise, it is reset.
N is reset.
C is data from bit 0 of source register.
Example
The HL register pair contains 4343h and memory location 4343h and the Carry flag con-
tain the following data.
Upon the execution of an RR (HL) instruction, location
4343h and the Carry flag now
contain:
Instruction M Cycles T States 4 MHz E.T.
RR r 2 8 (4, 4) 2.00
RR (HL) 4 15 (4, 4, 4, 3) 3.75
RR (IX+d) 6 23 (4, 4, 3, 5, 4, 3) 5.75
RR (lY+d) 6 23 (4, 4, 3, 5, 4, 3) 5.75
101110 11
76 4 10253
C
0
011101 10
76 4 10253
C
1
Z80 Instruction Set UM008011-0816
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SLA m
Operation
Op Code
SLA
Operand
m
The m operand is any of r, (HL), (IX+d), or (lY+d), as defined for the analogous RLC
instructions. In the assembled object code, the possible op code/operand combinations are
specified as follows:
CY
70
m
0
00 010
r*
11 0 11001
CB
11 0 11001
CB
11 1 01101
DD
11 0 11001
CB
11 1 01111
FD
11 0 11001
CB
SLA r*
SLA (HL)
SLA (IX+d)
SLA (IY+d)
d
d
00 0 10110
26
00 0 10110
26
00 0 10110
26
UM008011-0816 Z80 Instruction Description
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r identifies registers B, C, D, E, H, L, or A assembled as follows in the object code field:
Description
An arithmetic shift left 1 bit position is performed on the contents of operand m. The con-
tents of bit 7 are copied to the Carry flag. Bit 0 is the least-significant bit.
Condition Bits Affected
S is set if result is negative; otherwise, it is reset.
Z is set if result is 0; otherwise, it is reset.
H is reset.
P/V is set if parity is even; otherwise, it is reset.
N is reset.
C is data from bit 7.
Example
Register L contains the following data.
Register r
B
000
C
001
D
010
E
011
H
100
L
101
A
111
Instruction M Cycles T States 4 MHz E.T.
SLA r 2 8 (4, 4) 2.00
SLA (HL) 4 15 (4, 4, 4, 3) 3.75
SLA (IX+d) 6 23 (4, 4, 3, 5, 4, 3) 5.75
SLA (IY+d) 6 23 (4, 4, 3, 5, 4, 3) 5.75
10 1 01010
76 4 10253
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Upon the execution of an SLA L instruction, Register L and the Carry flag now contain:
01 0 10010
76 4 10253
C
1
UM008011-0816 Z80 Instruction Description
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233
SRA m
Operation
Op Code
SRA
Operand
m
The m operand is any of r, (HL), (IX+d), or (lY+d), as defined for the analogous RLC
instructions. In the assembled object code, the possible op code/operand combinations are
specified as follows:
CY
07
m
00 011
r*
11 0 11001
CB
11 0 11001
CB
11 1 01101
DD
11 0 11001
CB
11 1 01111
FD
11 0 11001
CB
SRA r*
SRA (HL)
SRA (IX+d)
SRA (IY+d)
d
d
00 0 10111
2E
00 0 10111
2E
00 0 10111
2E
Z80 Instruction Set UM008011-0816
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r identifies registers B, C, D, E, H, L, or A assembled as follows in the object code field:
Description
An arithmetic shift right 1 bit position is performed on the contents of operand m. The
contents of bit 0 are copied to the Carry flag and the previous contents of bit 7 remain
unchanged. Bit 0 is the least-significant bit.
Condition Bits Affected
S is set if result is negative; otherwise, it is reset.
Z is set if result is 0; otherwise, it is reset.
H is reset.
P/V is set if parity is even; otherwise, it is reset.
N is reset.
C is data from bit 0 of source register.
Example
Index Register IX contains 1000h and memory location 1003h contains the following
data.
Register r
B 000
C 001
D 010
E 011
H 100
L 101
A 111
Instruction M Cycles T States 4 MHz E.T.
SRA r 2 8 (4, 4) 2.00
SRA (HL) 4 15 (4, 4, 4, 3) 3.75
SRA (IX+d) 6 23 (4, 4, 3, 5, 4, 3) 5.75
SRA (lY+d) 6 23 (4, 4, 3, 5, 4, 3) 5.75
10 1 00011
76 4 10253
UM008011-0816 Z80 Instruction Description
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235
Upon the execution of an SRA (IX+3h) instruction, memory location 1003h and the
Carry flag now contain:
001110 11
76 4 10253
C
0
Z80 Instruction Set UM008011-0816
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SRL m
Operation
Op Code
SRL
Operand
m
The operand m is any of r, (HL), (IX+d), or (lY+d), as defined for the analogous RLC
instructions. In the assembled object code, the possible op code/operand combinations are
specified as follows:
CY
07
m
0
00 111
r*
11 0 11001
CB
11 0 11001
CB
11 1 01101
DD
11 0 11001
CB
11 1 01111
FD
11 0 11001
CB
SRL r*
SRL (HL)
SRL (IX+d)
SRL (IY+d)
d
d
00 1 10111
3E
00 1 10111
3E
00 1 10111
3E
UM008011-0816 Z80 Instruction Description
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r identifies registers B, C, D, E, H, L, or A.
Description
The contents of operand m are shifted right 1 bit position. The contents of bit 0 are copied
to the Carry flag, and bit 7 is reset. Bit 0 is the least-significant bit.
Condition Bits Affected
S is reset.
Z is set if result is 0; otherwise, it is reset.
H is reset.
P/V is set if parity is even; otherwise, it is reset.
N is reset.
C is data from bit 0 of source register.
Example
Register B contains the following data.
Upon the execution of an SRL B instruction, Register B and the Carry flag now contain:
Instruction M Cycles T States 4 MHz E.T.
SRL r 2 8 (4, 4) 2.00
SRL (HL) 4 15 (4, 4, 4, 3) 3.75
SRL (IX+d) 6 23 (4, 4, 3, 5, 4, 3) 5.75
SRL (lY+d) 6 23 (4, 4, 3, 5, 4, 3) 5.75
10 0 11101
76 4 10253
110100 10
76 4 10253
C
1
Z80 Instruction Set UM008011-0816
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RLD
Operation
Op Code
RLD
Operands
Description
The contents of the low-order four bits (bits 3, 2, 1, and 0) of the memory location (HL)
are copied to the high-order four bits (7, 6, 5, and 4) of that same memory location; the
previous contents of those high-order four bits are copied to the low-order four bits of the
Accumulator (Register A); and the previous contents of the low-order four bits of the
Accumulator are copied to the low-order four bits of memory location (HL). The contents
of the high-order bits of the Accumulator are unaffected.
(HL) refers to the memory location specified by the contents of the HL register pair.
Condition Bits Affected
S is set if the Accumulator is negative after an operation; otherwise, it is reset.
Z is set if the Accumulator is 0 after an operation; otherwise, it is reset.
H is reset.
M Cycles T States 4 MHz E.T.
5 18 (4, 4, 3, 4, 3) 4.50
47 03 47 03
A
11 0 01111
ED
01 0 11111
6F
Note:
UM008011-0816 Z80 Instruction Description
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P/V is set if the parity of the Accumulator is even after an operation; otherwise, it is reset.
N is reset.
C is not affected.
Example
The HL register pair contains 5000h and the Accumulator and memory location 5000h
contain the following data.
Upon the execution of an RLD instruction, the Accumulator and memory location
5000h
now contain:
01 1 10011
76 4 10253
Accumulator
00 1 01010
76 4 10253
(5000h)
01 1 11010
76 4 10253
Accumulator
00 1 10001
76 4 10253
(5000h)
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RRD
Operation
Op Code
RRD
Operands
Description
The contents of the low-order four bits (bits 3, 2, 1, and 0) of memory location (HL) are
copied to the low-order four bits of the Accumulator (Register A). The previous contents
of the low-order four bits of the Accumulator are copied to the high-order four bits (7, 6, 5,
and 4) of location (HL); and the previous contents of the high-order four bits of (HL) are
copied to the low-order four bits of (HL). The contents of the high-order bits of the Accu-
mulator are unaffected.
(HL) refers to the memory location specified by the contents of the HL register pair.
Condition Bits Affected
S is set if the Accumulator is negative after an operation; otherwise, it is reset.
Z is set if the Accumulator is 0 after an operation; otherwise, it is reset.
H is reset.
M Cycles T States 4 MHz E.T.
5 18 (4, 4, 3, 4, 3) 4.50
47 03 47 03
A
(HL)
11 0 01111
ED
01 0 11110
67
Note:
UM008011-0816 Z80 Instruction Description
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P/V is set if the parity of the Accumulator is even after an operation; otherwise, it is reset.
N is reset.
C is not affected.
Example
The HL register pair contains 5000h and the Accumulator and memory location 5000h
contain the following data.
Upon the execution of an RRD instruction, the Accumulator and memory location
5000h
now contain:
10 0 00100
76 4 10253
Accumulator
00 0 00010
76 4 10253
(5000h)
10 0 00000
76 4 10253
Accumulator
01 0 10000
76 4 10253
(5000h)
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Bit Set, Reset, and Test Group
The following bit set, reset, and test group instructions are each described in this section.
Simply click to jump to an instruction’s description to learn more.
BIT b, r
– see page 243
BIT b, (HL)
– see page 245
BIT b, (IX+d)
– see page 247
BIT b, (IY+d)
– see page 249
SET b, r
– see page 251
SET b, (HL)
– see page 253
SET b, (IX+d)
– see page 255
SET b, (IY+d)
– see page 257
RES b, m
– see page 259
UM008011-0816 Z80 Instruction Description
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243
BIT b, r
Operation
Z ← rb
Op Code
BIT
Operands
b, r
Description
This instruction tests bit b in register r and sets the Z flag accordingly. In the assembled
object code, operands b and r are specified as follows:
Condition Bits Affected
S is unknown.
Z is set if specified bit is 0; otherwise, it is reset.
Bit Tested b Register r
0 000 B 000
1 001 C 001
2 010 D 010
3 011 E 011
4 100 H 100
5 101 L 101
6 110 A 111
7 111
M Cycles T States 4 MHz E.T.
2 8 (4, 4) 4.50
01 b
r
11 0 11001
CB
Z80 Instruction Set UM008011-0816
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H is set.
P/V is unknown.
N is reset.
C is not affected.
Example
If bit 2 in Register B contains 0, then upon the execution of a BIT 2, B instruction, the Z
flag in the F Register contains 1, and bit 2 in Register B remains at 0. Bit 0 in Register B is
the least-significant bit.
UM008011-0816 Z80 Instruction Description
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245
BIT b, (HL)
Operation
Z ← (HL)b
Op Code
BIT
Operands
b, (HL)
Description
This instruction tests bit b in the memory location specified by the contents of the HL reg-
ister pair and sets the Z flag accordingly. In the assembled object code, operand b is speci-
fied as follows:
Condition Bits Affected
S is unknown.
Bit Tested b
0 000
1 001
2 010
3 011
4 100
5 101
6 110
1 111
M Cycles T States 4 MHz E.T.
3 12 (4, 4, 4) 4 3.00
11 0 11001
CB
01 b 101
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Z is set if specified bit is 0; otherwise, it is reset.
H is set.
P/V is unknown.
H is reset.
C is not affected.
Example
If the HL register pair contains 4444h, and bit 4 in the memory location 444h contains 1,
then upon the execution of a BIT 4, (HL) instruction, the Z flag in the F Register contains
0, and bit 4 in memory location
4444h remains at 1. Bit 0 in memory location 4444h is
the least-significant bit.
UM008011-0816 Z80 Instruction Description
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247
BIT b, (IX+d)
Operation
Z ← (IX+d)b
Op Code
BIT
Operands
b, (IX+d)
Description
This instruction tests bit b in the memory location specified by the contents of register pair
IX combined with the two’s complement displacement d and sets the Z flag accordingly.
In the assembled object code, operand b is specified as follows:
Bit Tested b
0 000
1 001
2 010
3 011
4 100
5 101
6 110
7 111
M Cycles T States 4 MHz E.T.
5 20 (4, 4, 3, 5, 4) 5.00
11 1 01101
DD
11 0 11001
CB
d
01 b 110
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Condition Bits Affected
S is unknown.
Z is set if specified bit is 0; otherwise, it is reset.
H is set.
P/V is unknown.
N is reset.
C is not affected.
Example
If Index Register IX contains 2000h and bit 6 in memory location 2004h contains 1, then
upon the execution of a BIT 6, (IX+
4h) instruction, the Z flag in the F Register contains a
0 and bit 6 in memory location
2004h still contains a 1. Bit 0 in memory location 2004h
is the least-significant bit.
UM008011-0816 Z80 Instruction Description
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249
BIT b, (IY+d)
Operation
Z ← (IY+d)b
Op Code
BIT
Operands
b, (lY+d)
Description
This instruction tests bit b in the memory location specified by the contents of register pair
IY combined with the two’s complement displacement d and sets the Z flag accordingly.
In the assembled object code, operand b is specified as follows.
Bit Tested b
0 000
1 001
2 010
3 011
4 100
5 101
6 110
7 111
M Cycles T States 4 MHz E.T.
5 20 (4, 4, 3, 5, 4) 5.00
11 1 01111
FD
11 0 11001
CB
d
01 b 110
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Condition Bits Affected
S is unknown.
Z is set if specified bit is 0; otherwise, it is reset.
H is set.
P/V is unknown.
H is reset.
C is not affected.
Example
If Index Register contains 2000h and bit 6 in memory location 2004h contains a 1, then
upon the execution of a BIT 6, (IY+
4h) instruction, the Z flag and the F Register still con-
tains a 0, and bit 6 in memory location
2004h still contains a 1. Bit 0 in memory location
2004h is the least-significant bit.
UM008011-0816 Z80 Instruction Description
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251
SET b, r
Operation
rb ← 1
Op Code
SET
Operands
b, r
Description
Bit b in register r (any of registers B, C, D, E, H, L, or A) is set. In the assembled object
code, operands b and r are specified as follows:
Condition Bits Affected
None.
Bit b Register r
0 000 B 000
1 001 C 001
2 010 D 010
3 011 E 011
4 100 H 100
5 101 L 101
6 110 A 111
7 111
M Cycles T States 4 MHz E.T.
2 8 (4, 4) 2.00
11 b
r
11 0 11001
CB
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Example
Upon the execution of a SET 4, A instruction, bit 4 in Register A is set. Bit 0 is the least-
significant bit.
UM008011-0816 Z80 Instruction Description
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253
SET b, (HL)
Operation
(HL)b ← 1
Op Code
SET
Operands
b, (HL)
Description
Bit b in the memory location addressed by the contents of register pair HL is set. In the
assembled object code, operand b is specified as follows:
Condition Bits Affected
None.
Bit Tested b
0 000
1 001
2 010
3 011
4 100
5 101
6 110
7 111
M Cycles T States 4 MHz E.T.
4 15 (4, 4, 4, 3) 3.75
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Example
If the HL register pair contains 3000h, then upon the execution of a SET 4, (HL) instruc-
tion, bit 4 in memory location
3000h is 1. Bit 0 in memory location 3000h is the least-sig-
nificant bit.
UM008011-0816 Z80 Instruction Description
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255
SET b, (IX+d)
Operation
(IX+d)b ← 1
Op Code
SET
Operands
b, (IX+d)
Description
Bit b in the memory location addressed by the sum of the contents of the IX register pair
and the two’s complement integer d is set. In the assembled object code, operand b is spec-
ified as follows:
Bit Tested b
0 000
1 001
2 010
3 011
4 100
5 101
6 110
7 111
M Cycles T States 4 MHz E.T.
6 23 (4, 4, 3, 5, 4, 3) 5.75
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Condition Bits Affected
None.
Example
If the index register contains 2000h, then upon the execution of a SET 0, (IX + 3h)
instruction, bit 0 in memory location
2003h is 1. Bit 0 in memory location 2003h is the
least-significant bit.
UM008011-0816 Z80 Instruction Description
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257
SET b, (IY+d)
Operation
(IY + d) b ← 1
Op Code
SET
Operands
b, (IY + d)
Description
Bit b in the memory location addressed by the sum of the contents of the IY register pair
and the two’s complement displacement d is set. In the assembled object code, operand b
is specified as follows:
Bit Tested b
0 000
1 001
2 010
3 011
4 100
5 101
6 110
7 111
M Cycles T States 4 MHz E.T.
6 23 (4, 4, 3, 5, 4, 3) 5.75
11 1 01111
FD
11 0 11001
CB
d
11 b 110
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Condition Bits Affected
None.
Example
If Index Register IY contains 2000h, then upon the execution of a Set 0, (IY+3h) instruc-
tion, bit 0 in memory location
2003h is 1. Bit 0 in memory location 2003h is the least-sig-
nificant bit.
UM008011-0816 Z80 Instruction Description
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259
RES b, m
Operation
sb ← 0
Op Code
RES
Operands
b, m
The b operand represents any bit (7 through 0) of the contents of the m operand, (any of r,
(HL), (IX+d), or (lY+d)) as defined for the analogous SET instructions. These possible op
code/operand combinations are assembled as follows in the object code:
11 0 11001
CB
11 0 11001
CB
11 1 01101
DD
11 0 11001
CB
d
11 1 01111
FD
11 0 11001
CB
d
RES b, rn
RES b, (HL)
RES b, (IX+d)
RES b, (IY+d)
10 b 110
10 b 110
10 b
r
10 b 110
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Description
Bit b in operand m is reset.
Condition Bits Affected
None.
Example
Upon the execution of a RES 6, D instruction, bit 6 in register 0 is reset. Bit 0 in the D
Register is the least-significant bit.
Bit b Register r
0 000 B 000
1 001 C 001
2 010 D 010
3 011 E 011
4 100 H 100
5 101 L 101
6 110 A 111
7 111
Instruction M Cycles T States 4 MHz E.T.
RES r 4 8 (4, 4) 2.00
RES (HL) 4 15 (4, 4, 4, 3) 3.75
RES (IX+d) 6 23 (4, 4, 3, 5, 4, 3) 5.75
RES (lY+d) 6 23 (4, 4, 3, 5, 4, 3) 5.75
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261
Jump Group
The following jump group instructions are each described in this section. Simply click to
jump to an instruction’s description to learn more.
JP nn
– see page 262
JP cc, nn
– see page 263
JR e
– see page 265
JR C, e
– see page 267
JR NC, e
– see page 269
JR Z, e
– see page 271
JR NZ, e
– see page 273
JP (HL)
– see page 275
JP (IX)
– see page 276
JP (IY)
– see page 277
DJNZ, e
– see page 278
Z80 Instruction Set UM008011-0816
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JP nn
Operation
PC ← nn
Op Code
JP
Operand
nn
The first operand in this assembled object code is the low-order byte of a two-byte address.
Description
Operand nn is loaded to register pair Program Counter (PC). The next instruction is
fetched from the location designated by the new contents of the PC.
Condition Bits Affected
None.
M Cycles T States 4 MHz E.T.
3 10 (4, 3, 3) 2.50
11 0 11000
C3
n
n
Note:
UM008011-0816 Z80 Instruction Description
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263
JP cc, nn
Operation
IF cc true, PC ← nn
Op Code
JP
Operands
cc, nn
The first n operand in this assembled object code is the low-order byte of a 2-byte memory
address.
Description
If condition cc is true, the instruction loads operand nn to register pair Program Counter
(PC), and the program continues with the instruction beginning at address nn. If condition
cc is false, the Program Counter is incremented as usual, and the program continues with
the next sequential instruction. Condition cc is programmed as one of eight statuses that
correspond to condition bits in the Flag Register (Register F). These eight statuses are
defined in the following table, which specifies the corresponding cc bit fields in the
assembled object code.
cc Condition
Relevant
Flag
000 Non-Zero (NZ) Z
001 Zero (Z) Z
010 No Carry (NC) C
011 Carry (C) C
100 Parity Odd (PO) P/V
101 Parity Even (PE) P/V
110 Sign Positive (P) S
111 Sign Negative (M) S
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Condition Bits Affected
None.
Example
If the Carry flag (i.e., the C flag in F Register) is set and address 1520h contains 03h, then
upon the execution of a JP C,
1520h instruction, the Program Counter contains 1520h
and, on the next machine cycle, the CPD fetches byte
03h from address 1520h.
M Cycles T States 4 MHz E.T.
3 10 (4, 3, 3) 2.50
UM008011-0816 Z80 Instruction Description
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265
JR e
Operation
PC ← PC + e
Op Code
JR
Operand
e
Description
This instruction provides for unconditional branching to other segments of a program. The
value of displacement e is added to the Program Counter (PC) and the next instruction is
fetched from the location designated by the new contents of the PC. This jump is mea-
sured from the address of the instruction op code and contains a range of –126 to +129
bytes. The assembler automatically adjusts for the twice incremented PC.
Condition Bits Affected
None.
Example
To jump forward five locations from address 480, the following assembly language state-
ment is used:
JR $+5
The resulting object code and final Program Counter value is shown in the following table:
M Cycles T States 4 MHz E.T.
3 12 (4, 3, 5) 3.00
00 1 00001
18
e–2
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Location Instruction
480 18
481 03
482 –
483 –
484 –
485 ←
PC after jump
UM008011-0816 Z80 Instruction Description
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267
JR C, e
Operation
If C = 0, continue
If C = 1, PC ← PC+ e
Op Code
JR
Operands
C, e
Description
This instruction provides for conditional branching to other segments of a program
depending on the results of a test on the Carry Flag. If the flag = 1, the value of displace-
ment e is added to the Program Counter (PC) and the next instruction is fetched from the
location designated by the new contents of the PC. The jump is measured from the address
of the instruction op code and contains a range of –126 to +129 bytes. The assembler auto-
matically adjusts for the twice incremented PC.
If the flag = 0, the next instruction executed is taken from the location following this
instruction. If condition is met
If condition is not met:
Condition Bits Affected
None.
M Cycles T States 4 MHz E.T.
3 12 (4, 3, 5) 3.00
M Cycles T States 4 MHz E.T.
2 7 (4, 3) 1.75
00 1 00011
38
e–2
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Example
The Carry flag is set and it is required to jump back four locations from 480. The assembly
language statement is
JR C, $–4
The resulting object code and final Program Counter value is shown in the following table:
Location Instruction
47C ← PC after jump
47D –
47E –
47F –
480 38
481 FA (two’s
complement – 6)
UM008011-0816 Z80 Instruction Description
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269
JR NC, e
Operation
If C = 1, continue
If C = 0, PC ← PC + e
Op Code
JR
Operands
NC, e
Description
This instruction provides for conditional branching to other segments of a program
depending on the results of a test on the Carry Flag. If the flag is equal to 0, the value of
displacement e is added to the Program Counter (PC) and the next instruction is fetched
from the location designated by the new contents of the PC. The jump is measured from
the address of the instruction op code and contains a range of –126 to +129 bytes. The
assembler automatically adjusts for the twice incremented PC.
If the flag = 1, the next instruction executed is taken from the location following this
instruction.
If the condition is met:
If the condition is not met:
Condition Bits Affected
None.
M Cycles T States 4 MHz E.T.
3 12 (4, 3, 5) 3.00
M Cycles T States 4 MHz E.T.
7 7 (4, 3) 1.75
00 1 00010
30
e–2
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Example
The Carry Flag is reset and it is required to repeat the jump instruction. The assembly lan-
guage statement is
JR NC, $
The resulting object code and Program Counter after the jump are:
Location Instruction
480 30
← PC after jump
481 00
UM008011-0816 Z80 Instruction Description
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271
JR Z, e
Operation
If Z = 0, continue
If Z = 1, PC ← PC + e
Op Code
JR
Operands
Z, e
Description
This instruction provides for conditional branching to other segments of a program
depending on the results of a test on the Zero Flag. If the flag = 1, the value of displace-
ment e is added to the Program Counter (PC) and the next instruction is fetched from the
location designated by the new contents of the PC. The jump is measured from the address
of the instruction op code and contains a range of –126 to +129 bytes. The assembler auto-
matically adjusts for the twice-incremented PC.
If the Zero Flag = 0, the next instruction executed is taken from the location following this
instruction.
If this condition is met, the following data results:
If this condition is not met, the following data results:
Condition Bits Affected
None.
M Cycles T States 4 MHz E.T.
3 12 (4, 3, 5) 3.00
M Cycles T States 4 MHz E.T.
2 7 (4, 3) 1.75
00 0 00011
28
e–2
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Example
The Zero Flag is set and it is required to jump forward five locations from address 300.
The following assembly language statement is used:
JR Z ,$ + 5
The resulting object code and final Program Counter value are:
Location Instruction
300 28
301 03
302
–
303 –
304 –
305 ← PC after jump
UM008011-0816 Z80 Instruction Description
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273
JR NZ, e
Operation
If Z = 1, continue
If Z = 0, PC ← pc + e
Op Code
JR
Operands
NZ, e
Description
This instruction provides for conditional branching to other segments of a program
depending on the results of a test on the Zero Flag. If the flag = 0, the value of displace-
ment e is added to the Program Counter (PC) and the next instruction is fetched from the
location designated by the new contents of the PC. The jump is measured from the address
of the instruction op code and contains a range of –126 to +129 bytes. The assembler auto-
matically adjusts for the twice incremented PC.
If the Zero Flag = 1, the next instruction executed is taken from the location following this
instruction.
If the condition is met:
If the condition is not met:
Condition Bits Affected
None.
M Cycles T States 4 MHz E.T.
3 12 (4, 3, 5) 3.00
M Cycles T States 4 MHz E.T.
2 7 (4, 3) 1.75
00 0 00010
20
e–2
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Example
The Zero Flag is reset and it is required to jump back four locations from 480. The assem-
bly language statement is
JR NZ, $–4
The resulting object code and final Program Counter value is:
Location Instruction
47C ← PC after jump
47D
–
47E –
47F –
480 20
481 FA (two’s
complement – 6)
UM008011-0816 Z80 Instruction Description
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JP (HL)
Operation
PC ← HL
Op Code
JP
Operand
(HL)
Description
The Program Counter (PC) is loaded with the contents of the HL register pair. The next
instruction is fetched from the location designated by the new contents of the PC.
Condition Bits Affected
None.
Example
If the Program Counter contains 1000h and the HL register pair contains 4800h, then
upon the execution of a JP (HL) instruction, the Program Counter contains
4800h.
M Cycles T States 4 MHz E.T.
141.00
11 0 01011
E9
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JP (IX)
Operation
pc ← IX
Op Code
JP
Operand
(IX)
Description
The Program Counter (PC) is loaded with the contents of the IX register pair. The next
instruction is fetched from the location designated by the new contents of the PC.
Condition Bits Affected
None.
Example
If the Program Counter contains 1000h and the IX register pair contains 4800h, then
upon the execution of a JP (IX) instruction, the Program Counter contains
4800h.
M Cycles T States 4 MHz E.T.
2 8 (4, 4) 2.00
11 1 01101
DD
11 0 01011
E9
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277
JP (IY)
Operation
PC ← IY
Op Code
JP
Operand
(IY)
Description
The Program Counter (PC) is loaded with the contents of the IY register pair. The next
instruction is fetched from the location designated by the new contents of the PC.
Condition Bits Affected
None.
Example
If the Program Counter contains 1000h and the IY register pair contains 4800h, then
upon the execution of a JP (IY) instruction, the Program Counter contains
4800h.
M Cycles T States 4 MHz E.T.
2 8 (4, 4) 2.00
11 1 01111
FD
11 0 01011
E9
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DJNZ, e
Operation
B ← B – 1
If B = 0, continue
If B ≠ 0, PC ← PC + e
Op Code
DJNZ
Operand
e
Description
This instruction is similar to the conditional jump instructions except that a register value
is used to determine branching. Register B is decremented, and if a nonzero value remains,
the value of displacement e is added to the Program Counter (PC). The next instruction is
fetched from the location designated by the new contents of the PC. The jump is measured
from the address of the instruction op code and contains a range of –126 to +129 bytes.
The assembler automatically adjusts for the twice incremented PC.
If the result of decrementing leaves B with a zero value, the next instruction executed is
taken from the location following this instruction.
if B ≠
0:
If B = 0:
M Cycles T States 4 MHz E.T.
3 13 (5,3, 5) 3.25
M Cycles T States 4 MHz E.T.
2 8 (5, 3) 2.00
00 1 00000
10
e–2
UM008011-0816 Z80 Instruction Description
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Condition Bits Affected
None.
Example
A typical software routine is used to demonstrate the use of the DJNZ instruction. This
routine moves a line from an input buffer (INBUF) to an output buffer (OUTBUF). It
moves the bytes until it finds a CR, or until it has moved 80 bytes, whichever occurs first.
LD 8, 80 ;Set up counter
LD HL, Inbuf ;Set up pointers
LD DE, Outbuf
LOOP: LID A, (HL) ;Get next byte from
;input buffer
LD (DE), A ;Store in output buffer
CP ODH ;Is it a CR?
JR Z, DONE ;Yes finished
INC HL ;Increment pointers
INC DE
DJNZ LOOP ;Loop back if 80
;bytes have not
;been moved
DONE:
Z80 Instruction Set UM008011-0816
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Call and Return Group
The following call and return group instructions are each described in this section. Simply
click to jump to an instruction’s description to learn more.
CALL nn
– see page 281
CALL cc, nn
– see page 283
RET
– see page 285
RET cc
– see page 286
RETI
– see page 288
RETN
– see page 290
RST p
– see page 292
UM008011-0816 Z80 Instruction Description
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281
CALL nn
Operation
(SP – 1) ← PCH, (SP – 2) ← PCL, PC ← nn
Op Code
CALL
Operand
nn
The first of the two n operands in the assembled object code above is the least-significant
byte of a 2-byte memory address.
Description
The current contents of the Program Counter (PC) are pushed onto the top of the external
memory stack. The operands nn are then loaded to the PC to point to the address in mem-
ory at which the first op code of a subroutine is to be fetched. At the end of the subroutine,
a RETurn instruction can be used to return to the original program flow by popping the top
of the stack back to the PC. The push is accomplished by first decrementing the current
contents of the Stack Pointer (register pair SP), loading the high-order byte of the PC con-
tents to the memory address now pointed to by the SP; then decrementing SP again, and
loading the low-order byte of the PC contents to the top of stack.
Because this process is a 3-byte instruction, the Program Counter was incremented by
three before the push is executed.
Condition Bits Affected
None.
M Cycles T States 4 MHz E.T.
5 17 (4, 3, 4, 3, 3) 4.25
11 0 01101
CD
n
n
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Example
The Program Counter contains 1A47h, the Stack Pointer contains 3002h, and memory
locations contain the following data.
If an instruction fetch sequence begins, the 3-byte instruction CD
3521h is fetched to the
CPU for execution. The mnemonic equivalent of this instruction is CALL
2135h. Upon
the execution of this instruction, memory address
3001h contains 1Ah, address 3000h
contains
4Ah, the Stack Pointer contains 3000h, and the Program Counter contains
2135h, thereby pointing to the address of the first op code of the next subroutine to be
executed.
Location Contents
1A47h CDh
IA48h 35h
1A49h 21h
UM008011-0816 Z80 Instruction Description
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283
CALL cc, nn
Operation
IF cc true: (sp – 1) ← PCH
(sp – 2) ← PCL, pc ← nn
Op Code
CALL
Operands
cc, nn
The first of the two n operands in the assembled object code above is the least-significant
byte of the 2-byte memory address.
Description
If condition cc is true, this instruction pushes the current contents of the Program Counter
(PC) onto the top of the external memory stack, then loads the operands nn to PC to point
to the address in memory at which the first op code of a subroutine is to be fetched. At the
end of the subroutine, a RETurn instruction can be used to return to the original program
flow by popping the top of the stack back to PC. If condition cc is false, the Program
Counter is incremented as usual, and the program continues with the next sequential
instruction. The stack push is accomplished by first decrementing the current contents of
the Stack Pointer (SP), loading the high-order byte of the PC contents to the memory
address now pointed to by SP; then decrementing SP again, and loading the low-order
byte of the PC contents to the top of the stack.
Because this process is a 3-byte instruction, the Program Counter was incremented by
three before the push is executed.
Condition cc is programmed as one of eight statuses that corresponds to condition bits in
the Flag Register (Register F). These eight statuses are defined in the following table,
which also specifies the corresponding cc bit fields in the assembled object code.
n
n
11 010
cc
Z80 Instruction Set UM008011-0816
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If cc is true:
If cc is false:
Condition Bits Affected
None.
Example
The C Flag in the F Register is reset, the Program Counter contains 1A47h, the Stack
Pointer contains
3002h, and memory locations contain the following data.
If an instruction fetch sequence begins, the 3-byte instruction
D43521h is fetched to the
CPU for execution. The mnemonic equivalent of this instruction is CALL NC,
2135h.
Upon the execution of this instruction, memory address
3001h contains 1Ah, address
3000h contains 4Ah, the Stack Pointer contains 3000h, and the Program Counter contains
2135h, thereby pointing to the address of the first op code of the next subroutine to be
executed.
cc Condition
Relevant
Flag
000 Non-Zero (NZ) Z
001 Zero (Z) Z
010 Non Carry (NC) C
011 Carry (C) Z
100 Parity Odd (PO) P/V
101 Parity Even (PE) P/V
110 Sign Positive (P) S
111 Sign Negative (M) S
M Cycles T States 4 MHz E.T.
5 17 (4, 3, 4, 3, 3) 4.25
M Cycles T States 4 MHz E.T.
3 10 (4, 3, 3) 2.50
Location Contents
1A47h D4h
1448h 35h
1A49h 21h
UM008011-0816 Z80 Instruction Description
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285
RET
Operation
pCL ← (sp), pCH ← (sp+1)
Op Code
RET
Operands
None.
Description
The byte at the memory location specified by the contents of the Stack Pointer (SP) Regis-
ter pair is moved to the low-order eight bits of the Program Counter (PC). The SP is now
incremented and the byte at the memory location specified by the new contents of this
instruction is fetched from the memory location specified by the PC. This instruction is
normally used to return to the main line program at the completion of a routine entered by
a CALL instruction.
Condition Bits Affected
None.
Example
The Program Counter contains 3535h, the Stack Pointer contains 2000h, memory loca-
tion
2000h contains B5h, and memory location 2001h contains 18h. Upon the execution
of a RET instruction, the Stack Pointer contains
2002h and the Program Counter contains
18B5h, thereby pointing to the address of the next program op code to be fetched.
M Cycles T States 4 MHz E.T.
3 10 (4, 3, 3) 2.50
11 0 01001
C9
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RET cc
Operation
If cc true: PCL ← (sp), pCH ← (sp+1)
Op Code
RET
Operand
cc
Description
If condition cc is true, the byte at the memory location specified by the contents of the
Stack Pointer (SP) Register pair is moved to the low-order eight bits of the Program Coun-
ter (PC). The SP is incremented and the byte at the memory location specified by the new
contents of the SP are moved to the high-order eight bits of the PC. The SP is incremented
again. The next op code following this instruction is fetched from the memory location
specified by the PC. This instruction is normally used to return to the main line program at
the completion of a routine entered by a CALL instruction. If condition cc is false, the PC
is simply incremented as usual, and the program continues with the next sequential
instruction. Condition cc is programmed as one of eight status that correspond to condition
bits in the Flag Register (Register F). These eight status are defined in the following table,
which also specifies the corresponding cc bit fields in the assembled object code.
cc Condition
Relevant
Flag
000 Non-Zero (NZ) Z
001 Zero (Z) Z
010 Non Carry (NC) C
011 Carry (C) C
100 Parity Odd (PO) P/V
101 Parity Even (PE) P/V
110 Sign Positive (P) S
111 Sign Negative (M) S
11 000
cc
UM008011-0816 Z80 Instruction Description
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287
If cc is true, then the following data is returned:
If cc is false, then the following data is returned:
Condition Bits Affected
None.
Example
The S flag in the F Register is set, the Program Counter contains 3535h, the Stack Pointer
contains
2000h, memory location 2000h contains B5h, and memory location 2001h con-
tains
18h. Upon the execution of a RET M instruction, the Stack Pointer contains 2002h
and the Program Counter contains
18B5h, thereby pointing to the address of the next pro-
gram op code to be fetched.
M Cycles T States 4 MHz E.T.
3 11 (5, 3, 3) 2.75
M Cycles T States 4 MHz E.T.
151.25
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RETI
Operation
Return from Interrupt
Op Code
RETI
Operands
None.
Description
This instruction is used at the end of a maskable interrupt service routine to:
• Restore the contents of the Program Counter (analogous to the RET instruction)
• Signal an I/O device that the interrupt routine is completed. The RETI instruction also
facilitates the nesting of interrupts, allowing higher priority devices to temporarily
suspend service of lower priority service routines. However, this instruction does not
enable interrupts that were disabled when the interrupt routine was entered. Before
doing the RETI instruction, the enable interrupt instruction (EI) should be executed to
allow recognition of interrupts after completion of the current service routine.
Condition Bits Affected
None.
Example
Assume that there are two interrupting devices, A and B, connected in a daisy-chain con-
figuration, with A having a higher priority than B.
M Cycles T States 4 MHz E.T.
4 14 (4, 4, 3, 3) 3.50
11 0 01111
ED
01 0 01101
4D
UM008011-0816 Z80 Instruction Description
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B generates an interrupt and is acknowledged. The interrupt enable out, IEO, of B goes
Low, blocking any lower priority devices from interrupting while B is being serviced.
Then A generates an interrupt, suspending service of B. The IEO of A goes Low, indicat-
ing that a higher priority device is being serviced. The A routine is completed and a RETI
is issued resetting the IEO of A, allowing the B routine to continue. A second RETI is
issued on completion of the B routine and the IE0 of B is reset (High), allowing lower-pri-
ority devices interrupt access.
A
B
IEI
IEO
IEI
IEO
+
INT
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RETN
Operation
Return from nonmaskable interrupt
Op Code
RETN
Operands
None.
Description
This instruction is used at the end of a nonmaskable interrupts service routine to restore
the contents of the Program Counter (analogous to the RET instruction). The state of IFF2
is copied back to IFF1 so that maskable interrupts are enabled immediately following the
RETN if they were enabled before the nonmaskable interrupt.
Condition Bits Affected
None.
Example
If the Stack Pointer contains 1000h and the Program Counter contains 1A45h when a
Nonmaskable Interrupt (NMI) signal is received, the CPU ignores the next instruction and
instead restarts, returning to memory address
0066h. The current Program Counter con-
tains
1A45h, which is pushed onto the external stack address of 0FFFh and 0FFEh, high-
order byte first, and
0066h is loaded onto the Program Counter. That address begins an
interrupt service routine that ends with a RETN instruction.
Upon the execution of a RETN instruction, the contents of the former Program Counter
are popped off the external memory stack, low-order first, resulting in the Stack Pointer
again containing
1000h. The program flow continues where it left off with an op code
fetch to address
1A45h, order-byte first, and 0066h is loaded onto the Program Counter.
M Cycles T States 4 MHz E.T.
4 14 (4, 4, 3, 3) 3.50
11 0 01111
ED
01 0 01100
45
UM008011-0816 Z80 Instruction Description
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That address begins an interrupt service routine that ends with a RETN instruction. Upon
the execution of a RETN instruction, the contents of the former Program Counter are
popped off the external memory stack, low-order first, resulting in stack pointer contents
of
1000h. The program flow continues where it left off with an op code fetch to address
1A45h.
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RST p
Operation
(SP – 1) ← PCH, (SP – 2) ← PCL, PCH ← 0, PCL ← P
Op Code
RST
Operand
p
Description
The current Program Counter (PC) contents are pushed onto the external memory stack,
and the Page 0 memory location assigned by operand p is loaded to the PC. Program exe-
cution then begins with the op code in the address now pointed to by PC. The push is per-
formed by first decrementing the contents of the Stack Pointer (SP), loading the high-order
byte of PC to the memory address now pointed to by SP, decrementing SP again, and load-
ing the low-order byte of PC to the address now pointed to by SP. The Restart instruction
allows for a jump to one of eight addresses indicated in the following table. The operand p
is assembled to the object code using the corresponding T state.
Because all addresses are stored in Page 0 of memory, the high-order byte of PC is loaded
with
00h. The number selected from the p column of the table is loaded to the low-order
byte of PC.
pt
00h 000
08h 001
10h 010
18h 011
20h 100
28h 101
30h 110
38h 111
11 t 111
UM008011-0816 Z80 Instruction Description
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293
Example
If the Program Counter contains 15B3h, then upon the execution of an RST 18h (object
code
1101111) instruction, the PC contains 0018h as the address of the next fetched op
code.
M Cycles T States 4 MHz E.T.
3 11 (5, 3, 3) 2.75
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Input and Output Group
The following input and output group instructions are each described in this section. Sim-
ply click to jump to an instruction’s description to learn more.
IN A, (n)
– see page 295
IN r (C)
– see page 296
INI
– see page 298
INIR
– see page 300
IND
– see page 302
INDR
– see page 304
OUT (n), A
– see page 306
OUT (C), r
– see page 307
OUTI
– see page 309
OTIR
– see page 311
OUTD
– see page 313
OTDR
– see page 315
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IN A, (n)
Operation
A ← (n)
Op Code
IN
Operands
A, (n)
Description
The operand n is placed on the bottom half (A0 through A7) of the address bus to select
the I/O device at one of 256 possible ports. The contents of the Accumulator also appear
on the top half (A8 through A15) of the address bus at this time. Then one byte from the
selected port is placed on the data bus and written to the Accumulator (Register A) in the
CPU.
Condition Bits Affected
None.
Example
The Accumulator contains 23h, and byte 7Bh is available at the peripheral device mapped
to I/O port address
01h. Upon the execution of an IN A, (01h) instruction, the Accumula-
tor contains
7Bh.
M Cycles T States 4 MHz LT.
3 11 (4, 3, 4) 2.75
11 1 11001
DB
n
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IN r (C)
Operation
r ← (C)
Op Code
IN
Operands
r, (C)
Description
The contents of Register C are placed on the bottom half (A0 through A7) of the address
bus to select the I/O device at one of 256 possible ports. The contents of Register B are
placed on the top half (A8 through A15) of the address bus at this time. Then one byte
from the selected port is placed on the data bus and written to register r in the CPU. Regis-
ter r identifies any of the CPU registers shown in the following table, which also indicates
the corresponding 3-bit r field for each. The flags are affected, checking the input data.
Register r
Flag 110 Undefined op code; set the flag
B 000
C 001
D 010
E 011
H 100
L 101
A 111
M Cycles T States 4 MHz E.T.
3 12 (4, 4, 4) 3.00
11 0 01111
ED
01 r 000
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Condition Bits Affected
S is set if input data is negative; otherwise, it is reset.
Z is set if input data is 0; otherwise, it is reset.
H is reset.
P/V is set if parity is even; otherwise, it is reset.
N is reset.
C is not affected.
Example
Register C contains 07h, Register B contains 10h, and byte 7Bh is available at the periph-
eral device mapped to I/O port address
07h. Upon the execution of an IN D, (C) com-
mand, the D Register contains
7Bh.
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INI
Operation
(HL) ← (C), B ← B – 1, HL ← HL + 1
Op Code
INI
Operands
None.
Description
The contents of Register C are placed on the bottom half (A0 through A7) of the address
bus to select the I/O device at one of 256 possible ports. Register B can be used as a byte
counter, and its contents are placed on the top half (A8 through A15) of the address bus at
this time. Then one byte from the selected port is placed on the data bus and written to the
CPU. The contents of the HL register pair are then placed on the address bus and the input
byte is written to the corresponding location of memory. Finally, the byte counter is decre-
mented and register pair HL is incremented.
Condition Bits Affected
S is unknown.
Z is set if B – 1 = 0; otherwise it is reset.
H is unknown.
P/V is unknown.
N is set.
C is not affected.
M Cycles T States 4 MHz E.T.
4 16 (4, 5, 3, 4) 4.00
11 0 01111
ED
10 0 10010
A2
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Example
Register C contains 07h, Register B contains 10h, the HL register pair contains 1000h,
and byte
7Bh is available at the peripheral device mapped to I/O port address 07h. Upon
the execution of an INI instruction, memory location
1000h contains 7Bh, the HL register
pair contains
1001h, and Register B contains 0Fh.
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INIR
Operation
(HL) ← (C), B ← B – 1, HL ← HL +1
Op Code
INIR
Operands
None.
Description
The contents of Register C are placed on the bottom half (A0 through A7) of the address
bus to select the I/O device at one of 256 possible ports. Register B is used as a byte coun-
ter, and its contents are placed on the top half (A8 through A15) of the address bus at this
time. Then one byte from the selected port is placed on the data bus and written to the
CPU. The contents of the HL register pair are placed on the address bus and the input byte
is written to the corresponding location of memory. Then register pair HL is incremented,
the byte counter is decremented. If decrementing causes B to go to 0, the instruction is ter-
minated. If B is not 0, the Program Counter is decremented by two and the instruction
repeated. Interrupts are recognized and two refresh cycles execute after each data transfer.
If B is set to 0 prior to instruction execution, 256 bytes of data are input.
If B ≠ 0:
If B = 0:
M Cycles T States 4 MHz E.T.
5 21 (4, 5, 3, 4, 5) 5.25
M Cycles T States 4 MHz E.T.
4 16 (4, 5, 3, 4) 4.00
11 0 01111
ED
10 1 10010
B2
Note:
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Condition Bits Affected
S is unknown.
Z is set.
H is unknown.
P/V is unknown.
N is set.
C is not affected.
Example
Register C contains 07h, Register B contains 03h, the HL register pair contains 1000h,
and the following sequence of bytes is available at the peripheral device mapped to I/O
port of address
07h.
Upon the execution of an INIR instruction, the HL register pair contains
1003h, Register
B contains a 0, and the memory locations contain the following data:
51h
A9h
03h
1000h 51h
1001h A9h
1002h 03h
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IND
Operation
(HL) ← (C), B ← B – 1, HL ← HL – 1
Op Code
IND
Operands
None.
Description
The contents of Register C are placed on the bottom half (A0 through A7) of the address
bus to select the I/O device at one of 256 possible ports. Register B can be used as a byte
counter, and its contents are placed on the top half (A8 through A15) of the address bus at
this time. Then one byte from the selected port is placed on the data bus and written to the
CPU. The contents of the HL register pair are placed on the address bus and the input byte
is written to the corresponding location of memory. Finally, the byte counter and register
pair HL are decremented.
Condition Bits Affected
S is unknown.
Z is set if B – 1 = 0; otherwise, it is reset.
H is unknown.
P/V is unknown.
N is set.
C is not affected.
M Cycles T States 4 MHz E.T.
4 16 (4, 5, 3, 4) 4.00
11 0 01111
ED
10 0 10011
AA
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Example
Register C contains 07h, Register B contains 10h, the HL register pair contains 1000h,
and byte
7Bh is available at the peripheral device mapped to I/O port address 07h. Upon
the execution of an IND instruction, memory location
1000h contains 7Bh, the HL regis-
ter pair contains
0FFFh, and Register B contains 0Fh.
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INDR
Operation
(HL) ← (C), B ← 131, HL ← HL1
Op Code
INDR
Operands
None.
Description
The contents of Register C are placed on the bottom half (A0 through A7) of the address
bus to select the I/O device at one of 256 possible ports. Register B is used as a byte coun-
ter, and its contents are placed on the top half (A8 through A15) of the address bus at this
time. Then one byte from the selected port is placed on the data bus and written to the
CPU. The contents of the HL register pair are placed on the address bus and the input byte
is written to the corresponding location of memory. Then HL and the byte counter are dec-
remented. If decrementing causes B to go to 0, the instruction is terminated. If B is not 0,
the Program Counter is decremented by two and the instruction repeated. Interrupts are
recognized and two refresh cycles are executed after each data transfer.
When B is set to 0 prior to instruction execution, 256 bytes of data are input.
If B ≠ 0:
If B = 0:
M Cycles T States 4 MHz E.T.
5 21 (4, 5, 3, 4, 5) 5.25
M Cycles T States 4 MHz E.T.
4 16 (4, 5, 3, 4) 4.00
11 0 01111
ED
10 1 10011
BA
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Condition Bits Affected
S is unknown.
Z is set.
H is unknown.
P/V is unknown.
N is set.
C is not affected.
Example
Register C contains 07h, Register B contains 03h, the HL register pair contains 1000h
and the following sequence of bytes is available at the peripheral device mapped to I/O
port address
07h:
Upon the execution of an INDR instruction, the HL register pair contains
0FFDh, Register
B contains a 0, and the memory locations contain the following data:
51h
A9h
03h
0FFEh 03h
0FFFh A9h
1000h 51h
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OUT (n), A
Operation
(n) ← A
Op Code
OUT
Operands
(n), A
Description
The operand n is placed on the bottom half (A0 through A7) of the address bus to select
the I/O device at one of 256 possible ports. The contents of the Accumulator (Register A)
also appear on the top half (A8 through A15) of the address bus at this time. Then the byte
contained in the Accumulator is placed on the data bus and written to the selected periph-
eral device.
Condition Bits Affected
None.
Example
If the Accumulator contains 23h, then upon the execution of an OUT (01h) instruction,
byte
23h is written to the peripheral device mapped to I/O port address 01h.
M Cycles T States 4 MHz E.T.
3 11 (4, 3, 4) 2.75
11 1 11000
D3
n
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OUT (C), r
Operation
(C) ← r
Op Code
OUT
Operands
(C), r
Description
The contents of Register C are placed on the bottom half (A0 through A7) of the address
bus to select the I/O device at one of 256 possible ports. The contents of Register B are
placed on the top half (A8 through A15) of the address bus at this time. Then the byte con-
tained in register r is placed on the data bus and written to the selected peripheral device.
Register r identifies any of the CPU registers shown in the following table, which also
shows the corresponding three-bit r field for each that appears in the assembled object
code.
Register r
B 000
C 001
D 010
E 011
H 100
L 101
A 111
M Cycles T States 4 MHz E.T.
3 12 (4, 4, 4) 3.00
11 0 01111
ED
01 r 001
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Condition Bits Affected
None.
Example
If Register C contains 01h and the D Register contains 5Ah, then upon the execution of an
OUT (C), D instruction, byte
5Ah is written to the peripheral device mapped to I/O port
address
01h.
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OUTI
Operation
(C) ← (HL), B ← B – 1, HL ← HL + 1
Op Code
OUTI
Operands
None.
Description
The contents of the HL register pair are placed on the address bus to select a location in
memory. The byte contained in this memory location is temporarily stored in the CPU.
Then, after the byte counter (B) is decremented, the contents of Register C are placed on
the bottom half (A0 through A7) of the address bus to select the I/O device at one of 256
possible ports. Register B can be used as a byte counter, and its decremented value is
placed on the top half (A8 through A15) of the address bus. The byte to be output is placed
on the data bus and written to a selected peripheral device. Finally, the register pair HL is
incremented.
Condition Bits Affected
S is unknown.
Z is set if B – 1 = 0; otherwise, it is reset.
H is unknown.
P/V is unknown.
N is set.
C is not affected.
M Cycles T States 4 MHz E.T.
4 16 (4, 5, 3, 4) 4.00
11 0 01111
ED
10 0 11010
A3
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Example
If Register C contains 07h, Register B contains 10h, the HL register pair contains 100014
and memory address
1000h contains 5914, then upon the execution of an OUTI instruc-
tion, Register B contains
0Fh, the HL register pair contains 1001h, and byte 59h is writ-
ten to the peripheral device mapped to I/O port address
07h.
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OTIR
Operation
(C) ← (HL), B ← B – 1, HL ← HL + 1
Op Code
OTIR
Operands
None.
Description
The contents of the HL register pair are placed on the address bus to select a location in
memory. The byte contained in this memory location is temporarily stored in the CPU.
Then, after the byte counter (B) is decremented, the contents of Register C are placed on
the bottom half (A0 through A7) of the address bus to select the I/O device at one of 256
possible ports. Register B can be used as a byte counter, and its decremented value is
placed on the top half (A8 through A15) of the address bus at this time. Next, the byte to
be output is placed on the data bus and written to the selected peripheral device. Then reg-
ister pair HL is incremented. If the decremented B Register is not 0, the Program Counter
(PC) is decremented by two and the instruction is repeated. If B has gone to 0, the instruc-
tion is terminated. Interrupts are recognized and two refresh cycles are executed after each
data transfer.
When B is set to 0 prior to instruction execution, the instruction outputs 256 bytes of data.
If B ≠ 0:
M Cycles T States 4 MHz E.T.
5 21 (4, 5, 3, 4, 5) 5.25
11 0 01111
ED
10 1 11010
B3
Note:
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If B = 0:
Condition Bits Affected
S is unknown.
Z is set.
H is unknown.
P/V is unknown.
N is set.
C is not affected.
Example
Register C contains 07h, Register B contains 03h, the HL register pair contains 1000h,
and memory locations contain the following data.
Upon the execution of an OTIR instruction, the HL register pair contains
1003h, Register
B contains a 0, and a group of bytes is written to the peripheral device mapped to I/O port
address
07h in the following sequence:
M Cycles T States 4 MHz E.T.
4 16 (4, 5, 3, 4) 4.00
1000h contains 51h
1001h contains A9h
1002h contains 03h
51h
A9h
03h
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OUTD
Operation
(C) ← (HL), B ← B – 1, HL ← HL – 1
Op Code
OUTD
Operands
None.
Description
The contents of the HL register pair are placed on the address bus to select a location in
memory. The byte contained in this memory location is temporarily stored in the CPU.
Then, after the byte counter (B) is decremented, the contents of Register C are placed on
the bottom half (A0 through A7) of the address bus to select the I/O device at one of 256
possible ports. Register B can be used as a byte counter, and its decremented value is
placed on the top half (A8 through A15) of the address bus at this time. Next, the byte to
be output is placed on the data bus and written to the selected peripheral device. Finally,
the register pair HL is decremented.
Condition Bits Affected
S is unknown.
Z is set if B – 1 = 0; otherwise, it is reset.
H is unknown.
P/V is unknown.
N is set.
C is not affected.
M Cycles T States 4 MHz E.T.
4 16 (4, 5, 3. 4) 4.00
11 0 01111
ED
10 0 11011
AB
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Example
If Register C contains 07h, Register B contains 10h, the HL register pair contains 1000h,
and memory location
1000h contains 59h, then upon the execution of an OUTD instruc-
tion, Register B contains
0Fh, the HL register pair contains 0FFFh, and byte 59h is writ-
ten to the peripheral device mapped to I/O port address
07h.
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OTDR
Operation
(C) ← (HL), B ← B – 1, HL ← HL – 1
Op Code
OTDR
Operands
None.
Description
The contents of the HL register pair are placed on the address bus to select a location in
memory. The byte contained in this memory location is temporarily stored in the CPU.
Then, after the byte counter (B) is decremented, the contents of Register C are placed on
the bottom half (A0 through A7) of the address bus to select the I/O device at one of 256
possible ports. Register B can be used as a byte counter, and its decremented value is
placed on the top half (A8 through A15) of the address bus at this time. Next, the byte to
be output is placed on the data bus and written to the selected peripheral device. Then, reg-
ister pair HL is decremented and if the decremented B Register is not 0, the Program
Counter (PC) is decremented by two and the instruction is repeated. If B has gone to 0, the
instruction is terminated. Interrupts are recognized and two refresh cycles are executed
after each data transfer.
When B is set to 0 prior to instruction execution, the instruction outputs 256 bytes of data.
If B ≠ 0:
M Cycles T States 4 MHz E.T.
5 21 (4, 5, 3, 4, 5) 5.25
11 0 01111
ED
10 1 11011
BB
Note:
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If B = 0:
Condition Bits Affected
S is unknown.
Z is set.
H is unknown.
P/V is unknown.
N is set.
C is not affected.
Example
Register C contains 07h, Register B contains 03h, the HL register pair contains 1000h,
and memory locations contain the following data.
Upon the execution of an OTDR instruction, the HL register pair contain
0FFDh, Register
B contains a 0, and a group of bytes is written to the peripheral device mapped to I/O port
address
07h in the following sequence:
M Cycles T States 4 MHz E.T.
4 16 (4, 5, 3, 4) 4.00
0FFEh 51h
0FFFh A9h
1000h 03h
03h
A9h
51h
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Customer Support
To share comments, get your technical questions answered, or report issues you may be
experiencing with our products, please visit Zilog’s Technical Support page at
http://support.zilog.com
.
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edition exists, please visit the Zilog website at http://www.zilog.com
.
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