Altair8800 Simulator

8080 Instruction Set

Conventions in instruction source:

D = Destination register (8 bit) S = Source register (8 bit)

RP = Register pair (16 bit)

# = 8 or 16 bit immediate operand a = 16 bit Memory address

p = 8 bit port address ccc = Conditional

Conventions in instruction encoding: db = Data byte (8 bit)

lb = Low byte of 16 bit value hb = High byte of 16 bit value pa = Port address (8 bit)

Dest and Source reg fields: 111=A (Accumulator) 000=B

001=C

010=D

011=E

100=H

101=L

110=M (Memory reference through address in H:L)

00=BC (B:C as 16 bit register) 01=DE (D:E as 16 bit register) 10=HL (H:L as 16 bit register)

11=SP (Stack pointer, refers to PSW (FLAGS:A) for PUSH/POP)

Condition code 'CCC' fields: (FLAGS: S Z x A x P x C) 000=NZ (Zero flag not set)

001=Z (Zero flag set) 010=NC (Carry flag not set) 011=C (Carry flag set)

100=PO (Parity flag not set - ODD) 101=PE (Parity flag set - EVEN) 110=P (Sign flag not set - POSITIVE) 111=M (Sign flag set - MINUS)

Inst	Encoding			Flags			Description
ACI	#	11001110		db	ZSCPA		Add	immediate to A with carry*
ADC	S	10001SSS			ZSCPA		Add	register to A with carry
ADD	S	10000SSS			ZSPCA		Add	register to A
ADI	#	11000110		db	ZSCPA		Add	immediate to A
ANA	S	10100SSS			ZSCPA		AND	register with A
ANI	#	11100110		db	ZSPCA		AND	immediate with A
CALL		a	11001101	lb	hb	-	Unconditional subroutine call
Cccc		a	11CCC100	lb	hb	-	Conditional subroutine call
CMA			00101111			-	Complement A
CMC			00111111			C	Complement Carry flag
CMP	S		10111SSS			ZSPCA	Compare register with A
CPI	#		11111110			ZSPCA	Compare immediate with A
DAA			00100111			ZSPCA	Decimal Adjust accumulator
DAD	R	P	00RP1001			C	Add register pair to HL (16 bit add)*
DCR	D		00DDD101			ZSPA	Decrement register*
DCX	R	P	00RP1011			-	Decrement register pair
DI			11110011			-	Disable interrupts
EI			11111011			-	Enable interrupts
HLT			01110110			-	Halt processor
IN p			11011011	pa		-	Read input port into A
INR	D		00DDD100			ZSPA	Increment register
INX Jccc	R	P a	00RP0011 11CCC010	lb	hb	- -	Increment register pair Conditional jump*
JMP	a		11000011	lb	hb	-	Unconditional jump*
LDA	a		00111010	lb	hb	-	Load A from memory
LDAX		RP	00RP1010	*1		-	Load indirect through BC or DE
LHLD		a	00101010	lb	hb	-	Load H:L from memory*
LXI	R	P,#	00RP0001	lb	hb	-	Load register pair immediate*
MOV	D	,S	01DDDSSS			-	Move register to register*
MVI	D	,#	00DDD110	db		-	Move immediate to register*
NOP			00000000			-	No operation
ORA	S		10110SSS			ZSPCA	OR register with A
ORI	#		11110110			ZSPCA	OR immediate with A
OUT	p		11010011	pa		-	Write A to output port
PCHL			11101001			-	Jump to address in H:L
POP	R	P	11RP0001	*2		*2	Pop register pair from the stack
PUSH		RP	11RP0101	*2		-	Push register pair on the stack
RAL			00010111			C	Rotate A left through carry*
RAR			00011111			C	Rotate A right through carry
Rccc			11CCC000			-	Conditional return from subroutine
RET			11001001			-	Unconditional return from subroutine
RLC			00000111			C	Rotate A left
RRC			00001111			C	Rotate A right
RST	n		11NNN111			-	Restart (Call n*8)
SBB	S		10011SSS			ZSCPA	Subtract register from A with borrow
SBI	#		11011110	db		ZSCPA	Subtract immediate from A with borrow
SHLD		a	00100010	lb	hb	-	Store H:L to memory*
SPHL			11111001			-	Set SP to content of H:L
STA	a		00110010	lb	hb	-	Store A to memory
STAX		RP	00RP0010	*1		-	Store indirect through BC or DE
STC			00110111			C	Set Carry flag
SUB	S		10010SSS			ZSCPA	Subtract register from A
SUI	#		11010110	db		ZSCPA	Subtract immediate from A
XCHG			11101011			-	Exchange DE and HL content
XRA	S		10101SSS			ZSPCA	Exclusive OR register with A
XRI	#		11101110	db		ZSPCA	Exclusive OR immediate with A
XTHL			11100011			-	Swap H:L with top word on stack

*1 = Only RP=00(BC) and 01(DE) are allowed for LDAX/STAX

*2 = RP=11 refers to PSW for PUSH/POP (cannot push/pop SP).

When PSW is POP'd, ALL flags are affected.

Encoding			Inst			Flags	Description
00000000			NOP			-	No operation
00000111			RLC			C	Rotate A left
00001111			RRC			C	Rotate A right
00010111			RAL			C	Rotate A left through carry*
00011111			RAR			C	Rotate A right through carry
00100010	lb	hb	SHLD		a	-	Store H:L to memory*
00100111			DAA			ZSPCA	Decimal Adjust accumulator
00101010	lb	hb	LHLD		a	-	Load H:L from memory*
00101111			CMA			-	Complement A
00110010	lb	hb	STA	a		-	Store A to memory
00110111			STC			C	Set Carry flag
00111010	lb	hb	LDA	a		-	Load A from memory
00111111			CMC			C	Complement Carry flag
00DDD100			INR	D		ZSPA	Increment register
00DDD101			DCR	D		ZSPA	Decrement register*
00DDD110	db		MVI	D,#		-	Move immediate to register*
00RP0001	lb	hb	LXI	RP,#		-	Load register pair immediate*
00RP0010	*1		STAX RP			- Store indirect through BC or DE
00RP0011			INX RP			- Increment register pair
00RP1001			DAD RP			C Add register pair to HL (16 bit add)*
00RP1010	*1		LDAX RP			- Load indirect through BC or DE
00RP1011			DCX RP			- Decrement register pair
01110110			HLT			- Halt processor
01DDDSSS			MOV D,S			- Move register to register*
10000SSS			ADD S			ZSPCA Add register to A
10001SSS			ADC S			ZSCPA Add register to A with carry
10010SSS			SUB S			ZSCPA Subtract register from A
10011SSS			SBB S			ZSCPA Subtract register from A with borrow
10100SSS			ANA S			ZSCPA AND register with A
10101SSS			XRA S			ZSPCA Exclusive OR register with A
10110SSS			ORA S			ZSPCA OR register with A
10111SSS			CMP S			ZSPCA Compare register with A
11000011	lb	hb	JMP a			- Unconditional jump*
11000110	db		ADI #			ZSCPA Add immediate to A
11001001			RET			- Unconditional return from subroutine
11001101	lb	hb	CALL a			- Unconditional subroutine call
11001110	db		ACI	#		ZSCPA	Add immediate to A with carry*
11010011	pa	OUT		p	-		Write A to output port
11010110	db	SUI		#	ZSCPA		Subtract immediate from	A
11011011	pa	IN p			-		Read input port into A
11011110	db	SBI		#	ZSCPA		Subtract immediate from	A with borrow
11100011 XTHL - Swap H:L with top word on stack
11100110	db	ANI		#	ZSPCA		AND immediate with	A
11101001		PCHL			-		Jump to address in	H:L
11101011		XCHG			-		Exchange DE and HL	content
11101110	db		XRI	#		ZSPCA Exclusive OR immediate with A
11110011			DI			- Disable interrupts
11110110			ORI	#		ZSPCA OR immediate with A
11111001			SPHL			- Set SP to content of H:L
11111011			EI			- Enable interrupts
11111110			CPI	#		ZSPCA Compare immediate with A
11CCC000			Rccc			- Conditional return from subroutine
11CCC010	lb	hb	Jccc		a	- Conditional jump*
11CCC100	lb	hb	Cccc		a	- Conditional subroutine call
11NNN111			RST	n		- Restart (Call n*8)
11RP0001	*2		POP	R	P	*2 Pop register pair from the stack
11RP0101 *2 PUSH RP - Push register pair on the stack

*1 = Only RP=00(BC) and 01(DE) are allowed for LDAX/STAX

*2 = RP=11 refers to PSW for PUSH/POP (cannot push/pop SP).

When PSW is POP'd, ALL flags are affected.

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