NAME

gbz80 —

CPU opcode reference

DESCRIPTION

This is the list of opcodes supported by rgbasm(1), including a short description, the number of bytes needed to encode them and the number of CPU cycles at 1MHz (or 2MHz in GBC dual speed mode) needed to complete them.

Note: All arithmetic/logic operations that use register A as destination can omit the destination as it is assumed it's register A. The following two lines have the same effect:

OR A,B
OR B

LEGEND

List of abbreviations used in this document.

r8

Any of the 8-bit registers (A, B, C, D, E, H, L).

r16

Any of the general-purpose 16-bit registers (BC, DE, HL).

n8

8-bit integer constant.

n16

16-bit integer constant.

e8

8-bit offset (-128 to 127).

u3

3-bit unsigned integer constant (0 to 7).

cc

Condition codes:

Z:: Execute if Z is set.
NZ:: Execute if Z is not set.
C:: Execute if C is set.
NC:: Execute if C is not set.

vec

One of the RST vectors (0x00, 0x08, 0x10, 0x18, 0x20, 0x28, 0x30 and 0x38).

INSTRUCTION OVERVIEW

Bit Operations Instructions

BIT u3,r8
BIT u3,[HL]
RES u3,r8
RES u3,[HL]
SET u3,r8
SET u3,[HL]
SWAP r8
SWAP [HL]

Bit Shift Instructions

RL r8
RL [HL]
RLA
RLC r8
RLC [HL]
RLCA
RR r8
RR [HL]
RRA
RRC r8
RRC [HL]
RRCA
SLA r8
SLA [HL]
SRA r8
SRA [HL]
SRL r8
SRL [HL]

Load Instructions

LD r8,r8
LD r8,n8
LD r16,n16
LD [HL],r8
LD [HL],n8
LD r8,[HL]
LD [r16],A
LD [n16],A
LD [$FF00+n8],A
LD [$FF00+C],A
LD A,[r16]
LD A,[n16]
LD A,[$FF00+n8]
LD A,[$FF00+C]
LD [HL+],A
LD [HL-],A
LD A,[HL+]
LD A,[HL-]

Jumps and Subroutines

CALL n16
CALL cc,n16
JP HL
JP n16
JP cc,n16
JR e8
JR cc,e8
RET cc
RET
RETI
RST vec

Stack Operations Instructions

ADD HL,SP
ADD SP,e8
DEC SP
INC SP
LD SP,n16
LD [n16],SP
LD HL,SP+e8
LD SP,HL
POP AF
POP r16
PUSH AF
PUSH r16

Miscellaneous Instructions

CCF
CPL
DAA
DI
EI
HALT
NOP
SCF
STOP

INSTRUCTION REFERENCE

ADC A,r8

Add the value in r8 plus the carry flag to A.

Cycles: 1

Bytes: 1

Flags:

Z: Set if result is 0.
N: 0
H: Set if overflow from bit 3.
C: Set if overflow from bit 7.

ADC A,[HL]

Add the value pointed by HL plus the carry flag to A.

Cycles: 2

Bytes: 1

Flags: See ADC A,r8

ADC A,n8

Add the value n8 plus the carry flag to A.

Cycles: 2

Bytes: 2

Flags: See ADC A,r8

ADD A,r8

Add the value in r8 to A.

Cycles: 1

Bytes: 1

Flags:

Z: Set if result is 0.
N: 0
H: Set if overflow from bit 3.
C: Set if overflow from bit 7.

ADD A,[HL]

Add the value pointed by HL to A.

Cycles: 2

Bytes: 1

Flags: See ADD A,r8

ADD A,n8

Add the value n8 to A.

Cycles: 2

Bytes: 2

Flags: See ADD A,r8

ADD HL,r16

Add the value in r16 to HL.

Cycles: 2

Bytes: 1

Flags:

N: 0
H: Set if overflow from bit 11.
C: Set if overflow from bit 15.

ADD HL,SP

Add the value in SP to HL.

Cycles: 2

Bytes: 1

Flags: See ADD HL,r16

ADD SP,e8

Add the signed value e8 to SP.

Cycles: 4

Bytes: 2

Flags:

Z: 0
N: 0
H: Set if overflow from bit 3.
C: Set if overflow from bit 7.

AND A,r8

Bitwise AND between the value in r8 and A.

Cycles: 1

Bytes: 1

Flags:

Z: Set if result is 0.
N: 0
H: 1
C: 0

AND A,[HL]

Bitwise AND between the value pointed by HL and A.

Cycles: 2

Bytes: 1

Flags: See AND A,r8

AND A,n8

Bitwise AND between the value in n8 and A.

Cycles: 2

Bytes: 2

Flags: See AND A,r8

BIT u3,r8

Test bit u3 in register r8, set the zero flag if bit not set.

Cycles: 2

Bytes: 2

Flags:

Z: Set if the selected bit is 0.
N: 0
H: 1

BIT u3,[HL]

Test bit u3 in the byte pointed by HL, set the zero flag if bit not set.

Cycles: 3

Bytes: 2

Flags: See BIT u3,r8

CALL n16

Call address n16.

Cycles: 6

Bytes: 3

Flags: None affected.

CALL cc,n16

Call address n16 if condition cc is met.

Cycles: 6/3

Bytes: 3

Flags: None affected.

CCF

Complement Carry Flag.

Cycles: 1

Bytes: 1

Flags:

N: 0
H: 0
C: Complemented.

CP A,r8

Subtract the value in r8 from A and set flags accordingly, but don't store the result.

Cycles: 1

Bytes: 1

Flags:

Z: Set if result is 0.
N: 1
H: Set if no borrow from bit 4.
C: Set if no borrow (set if r8 > A).

CP A,[HL]

Subtract the value pointed by HL from A and set flags accordingly, but don't store the result.

Cycles: 2

Bytes: 1

Flags: See CP A,r8

CP A,n8

Subtract the value n8 from A and set flags accordingly, but don't store the result.

Cycles: 2

Bytes: 2

Flags: See CP A,r8

CPL

Complement accumulator (A = ~A).

Cycles: 1

Bytes: 1

Flags:

N: 1
H: 1

DAA

Decimal adjust register A to get a correct BCD representation after an arithmetic instruction.

Cycles: 1

Bytes: 1

Flags:

Z: Set if result is 0.
H: 0
C: Set or reset depending on the operation.

DEC r8

Decrement value in register r8 by 1.

Cycles: 1

Bytes: 1

Flags:

Z: Set if result is 0.
N: 1
H: Set if no borrow from bit 4.

DEC [HL]

Decrement the value pointed by HL by 1.

Cycles: 3

Bytes: 1

Flags: See DEC r8

DEC r16

Decrement value in register r16 by 1.

Cycles: 2

Bytes: 1

Flags: None affected.

DEC SP

Decrement value in register SP by 1.

Cycles: 2

Bytes: 1

Flags: None affected.

DI

Disable Interrupts.

Cycles: 1

Bytes: 1

Flags: None affected.

EI

Enable Interrupts.

Cycles: 1

Bytes: 1

Flags: None affected.

HALT

Enter CPU low power mode.

Cycles: -

Bytes: 1

Flags: None affected.

INC r8

Increment value in register r8 by 1.

Cycles: 1

Bytes: 1

Flags:

Z: Set if result is 0.
N: 0
H: Set if overflow from bit 3.

INC [HL]

Increment the value pointed by HL by 1.

Cycles: 3

Bytes: 1

Flags: See INC r8

INC r16

Increment value in register r16 by 1.

Cycles: 2

Bytes: 1

Flags: None affected.

INC SP

Increment value in register SP by 1.

Cycles: 2

Bytes: 1

Flags: None affected.

JP n16

Absolute jump to address n16.

Cycles: 4

Bytes: 3

Flags: None affected.

JP cc,n16

Absolute jump to address n16 if condition cc is met.

Cycles: 4/3

Bytes: 3

Flags: None affected.

JP HL

Jump to address in HL, that is, load PC with value in register HL.

Cycles: 1

Bytes: 1

Flags: None affected.

JR e8

Relative jump by adding e8 to the current address.

Cycles: 3

Bytes: 2

Flags: None affected.

JR cc,e8

Relative jump by adding e8 to the current address if condition cc is met.

Cycles: 3/2

Bytes: 2

Flags: None affected.

LD r8,r8

Store value in register on the right into register on the left.

Cycles: 1

Bytes: 1

Flags: None affected.

LD r8,n8

Load value n8 into register r8.

Cycles: 2

Bytes: 2

Flags: None affected.

LD r16,n16

Load value n16 into register r16.

Cycles: 3

Bytes: 3

Flags: None affected.

LD [HL],r8

Store value in register r8 into byte pointed by register HL.

Cycles: 2

Bytes: 1

Flags: None affected.

LD [HL],n8

Store value n8 into byte pointed by register HL.

Cycles: 3

Bytes: 2

Flags: None affected.

LD r8,[HL]

Load value into register r8 from byte pointed by register HL.

Cycles: 2

Bytes: 1

Flags: None affected.

LD [r16],A

Store value in register A into address pointed by register r16.

Cycles: 2

Bytes: 1

Flags: None affected.

LD [n16],A

Store value in register A into address n16.

Cycles: 4

Bytes: 3

Flags: None affected.

LD [$FF00+n8],A

Store value in register A into high RAM or I/O registers.

The following synonym forces this encoding: LDH [$FF00+n8],A

Cycles: 3

Bytes: 2

Flags: None affected.

LD [$FF00+C],A

Store value in register A into high RAM or I/O registers.

Cycles: 2

Bytes: 1

Flags: None affected.

LD A,[r16]

Load value in register A from address pointed by register r16.

Cycles: 2

Bytes: 1

Flags: None affected.

LD A,[n16]

Load value in register A from address n16.

Cycles: 4

Bytes: 3

Flags: None affected.

LD A,[$FF00+n8]

Load value in register A from high RAM or I/O registers.

The following synonym forces this encoding: LDH A,[$FF00+n8]

Cycles: 3

Bytes: 2

Flags: None affected.

LD A,[$FF00+C]

Load value in register A from high RAM or I/O registers.

Cycles: 2

Bytes: 1

Flags: None affected.

LD [HL+],A

Store value in register A into byte pointed by HL and post-increment HL.

Cycles: 2

Bytes: 1

Flags: None affected.

LD [HL-],A

Store value in register A into byte pointed by HL and post-decrement HL.

Cycles: 2

Bytes: 1

Flags: None affected.

LD A,[HL+]

Load value into register A from byte pointed by HL and post-increment HL.

Cycles: 2

Bytes: 1

Flags: None affected.

LD A,[HL-]

Load value into register A from byte pointed by HL and post-decrement HL.

Cycles: 2

Bytes: 1

Flags: None affected.

LD SP,n16

Load value n16 into register SP.

Cycles: 3

Bytes: 3

Flags: None affected.

LD [n16],SP

Store SP into addresses n16 (LSB) and n16 + 1 (MSB).

Cycles: 5

Bytes: 3

Flags: None affected.

LD HL,SP+e8

Add the signed value e8 to SP and store the result in HL.

Cycles: 3

Bytes: 2

Flags:

Z: 0
N: 0
H: Set if overflow from bit 3.
C: Set if overflow from bit 7.

LD SP,HL

Load register HL into register SP.

Cycles: 2

Bytes: 1

Flags: None affected.

NOP

No operation.

Cycles: 1

Bytes: 1

Flags: None affected.

OR A,r8

Bitwise OR between the value in r8 and A.

Cycles: 1

Bytes: 1

Flags:

Z: Set if result is 0.
N: 0
H: 0
C: 0

OR A,[HL]

Bitwise OR between the value pointed by HL and A.

Cycles: 2

Bytes: 1

Flags: See OR A,r8

OR A,n8

Bitwise OR between the value in n8 and A.

Cycles: 2

Bytes: 2

Flags: See OR A,r8

POP AF

Pop register AF from the stack.

Cycles: 3

Bytes: 1

Flags:

Z: Set from bit 7 of the popped low byte.
N: Set from bit 6 of the popped low byte.
H: Set from bit 5 of the popped low byte.
C: Set from bit 4 of the popped low byte.

POP r16

Pop register r16 from the stack.

Cycles: 3

Bytes: 1

Flags: None affected.

PUSH AF

Push register AF into the stack. The low byte's bit 7 corresponds to the Z flag, its bit 6 to the N flag, bit 5 to the H flag, and bit 4 to the C flag. Bits 3 to 0 are reset.

Cycles: 4

Bytes: 1

Flags: None affected.

PUSH r16

Push register r16 into the stack.

Cycles: 4

Bytes: 1

Flags: None affected.

RES u3,r8

Set bit u3 in register r8 to 0.

Cycles: 2

Bytes: 2

Flags: None affected.

RES u3,[HL]

Set bit u3 in the byte pointed by HL to 0.

Cycles: 4

Bytes: 2

Flags: None affected.

RET

Return from subroutine.

Cycles: 4

Bytes: 1

Flags: None affected.

RET cc

Return from subroutine if condition cc is met.

Cycles: 5/2

Bytes: 1

Flags: None affected.

RETI

Return from subroutine and enable interrupts.

Cycles: 4

Bytes: 1

Flags: None affected.

RL r8

Rotate register r8 left through carry.

C <- [7 <- 0] <- C

Cycles: 2

Bytes: 2

Flags:

Z: Set if result is 0.
N: 0
H: 0
C: Set according to result.

RL [HL]

Rotate value pointed by HL left through carry.

C <- [7 <- 0] <- C

Cycles: 4

Bytes: 2

Flags: See RL r8

RLA

Rotate register A left through carry.

C <- [7 <- 0] <- C

Cycles: 1

Bytes: 1

Flags:

Z: 0
N: 0
H: 0
C: Set according to result.

RLC r8

Rotate register r8 left.

C <- [7 <- 0] <- [7]

Cycles: 2

Bytes: 2

Flags:

Z: Set if result is 0.
N: 0
H: 0
C: Set according to result.

RLC [HL]

Rotate value pointed by HL left.

C <- [7 <- 0] <- [7]

Cycles: 4

Bytes: 2

Flags: See RLC r8

RLCA

Rotate register A left.

C <- [7 <- 0] <- [7]

Cycles: 1

Bytes: 1

Flags:

Z: 0
N: 0
H: 0
C: Set according to result.

RR r8

Rotate register r8 right through carry.

C -> [7 -> 0] -> C

Cycles: 2

Bytes: 2

Flags:

Z: Set if result is 0.
N: 0
H: 0
C: Set according to result.

RR [HL]

Rotate value pointed by HL right through carry.

C -> [7 -> 0] -> C

Cycles: 4

Bytes: 2

Flags: See RR r8

RRA

Rotate register A right through carry.

C -> [7 -> 0] -> C

Cycles: 1

Bytes: 1

Flags:

Z: 0
N: 0
H: 0
C: Set according to result.

RRC r8

Rotate register r8 right.

[0] -> [7 -> 0] -> C

Cycles: 2

Bytes: 2

Flags:

Z: Set if result is 0.
N: 0
H: 0
C: Set according to result.

RRC [HL]

Rotate value pointed by HL right.

[0] -> [7 -> 0] -> C

Cycles: 4

Bytes: 2

Flags: See RRC r8

RRCA

Rotate register A right.

[0] -> [7 -> 0] -> C

Cycles: 1

Bytes: 1

Flags:

Z: 0
N: 0
H: 0
C: Set according to result.

RST vec

Call restart vector vec.

Cycles: 4

Bytes: 1

Flags: None affected.

SBC A,r8

Subtract the value in r8 and the carry flag from A.

Cycles: 1

Bytes: 1

Flags:

Z: Set if result is 0.
N: 1
H: Set if no borrow from bit 4.
C: Set if no borrow (set if r8 > A).

SBC A,[HL]

Subtract the value pointed by HL and the carry flag from A.

Cycles: 2

Bytes: 1

Flags: See SBC A,r8

SBC A,n8

Subtract the value n8 and the carry flag from A.

Cycles: 2

Bytes: 2

Flags: See SBC A,r8

SCF

Set Carry Flag.

Cycles: 1

Bytes: 1

Flags:

N: 0
H: 0
C: 1

SET u3,r8

Set bit u3 in register r8 to 1.

Cycles: 2

Bytes: 2

Flags: None affected.

SET u3,[HL]

Set bit u3 in the byte pointed by HL to 1.

Cycles: 4

Bytes: 2

Flags: None affected.

SLA r8

Shift left arithmetic register r8.

C <- [7 <- 0] <- 0

Cycles: 2

Bytes: 2

Flags:

Z: Set if result is 0.
N: 0
H: 0
C: Set according to result.

SLA [HL]

Shift left arithmetic value pointed by HL.

C <- [7 <- 0] <- 0

Cycles: 4

Bytes: 2

Flags: See SLA r8

SRA r8

Shift right arithmetic register r8.

[7] -> [7 -> 0] -> C

Cycles: 2

Bytes: 2

Flags:

Z: Set if result is 0.
N: 0
H: 0
C: Set according to result.

SRA [HL]

Shift right arithmetic value pointed by HL.

[7] -> [7 -> 0] -> C

Cycles: 4

Bytes: 2

Flags: See SRA r8

SRL r8

Shift right logic register r8.

0 -> [7 -> 0] -> C

Cycles: 2

Bytes: 2

Flags:

Z: Set if result is 0.
N: 0
H: 0
C: Set according to result.

SRL [HL]

Shift right logic value pointed by HL.

0 -> [7 -> 0] -> C

Cycles: 4

Bytes: 2

Flags: See SRA r8

STOP

Enter CPU very low power mode. Also used to switch between double and normal speed CPU modes in GBC.

Cycles: -

Bytes: 2

Flags: None affected.

SUB A,r8

Subtract the value in r8 from A.

Cycles: 1

Bytes: 1

Flags:

Z: Set if result is 0.
N: 1
H: Set if no borrow from bit 4.
C: Set if no borrow (set if r8 > A).

SUB A,[HL]

Subtract the value pointed by HL from A.

Cycles: 2

Bytes: 1

Flags: See SUB A,r8

SUB A,n8

Subtract the value n8 from A.

Cycles: 2

Bytes: 2

Flags: See SUB A,r8

SWAP r8

Swap upper 4 bits in register r8 and the lower ones.

Cycles: 2

Bytes: 2

Flags:

Z: Set if result is 0.
N: 0
H: 0
C: 0

SWAP [HL]

Swap upper 4 bits in the byte pointed by HL and the lower ones.

Cycles: 4

Bytes: 2

Flags: See SWAP r8

XOR A,r8

Bitwise XOR between the value in r8 and A.

Cycles: 1

Bytes: 1

Flags:

Z: Set if result is 0.
N: 0
H: 0
C: 0

XOR A,[HL]

Bitwise XOR between the value pointed by HL and A.

Cycles: 2

Bytes: 1

Flags: See XOR A,r8

XOR A,n8

Bitwise XOR between the value in n8 and A.

Cycles: 2

Bytes: 2

Flags: See XOR A,r8

HISTORY

rgbds was originally written by Carsten Sørensen as part of the ASMotor package, and was later packaged in RGBDS by Justin Lloyd. It is now maintained by a number of contributors at https://github.com/rednex/rgbds.