Atari "Sally" (6502) Instruction Set

Instruction Descriptions (listed alphabetically):

MNEMONIC	OPERATION	N	Z	C	I	D	V
ADC	A' = A + M + C ¹	X	X	X	.	.	X
ANC^*	A' = A /\ M	X	X	A'₇	.	.	.
AND	A' = A /\ M	X	X	.	.	.	.
ARR^*	A' = ((A /\ M) >> 1) + (C * 80)	X	X	A'₆	.	.	X⁴
ASL	M' = M << 1	X	X	X	.	.	.
ASR^*	A' = (A /\ M) >> 1	X	X	X	.	.	.
ASX^*	X' = (X /\ A) - M	X	X	X	.	.	.
AX7^*	M' = A /\ X /\ 07	.	.	.	.	.	.
AXE^*	A' = (A \/ EE) /\ X /\ M	X	X	.	.	.	.
BCC	IF NOT C THEN PC' = PC + M	.	.	.	.	.	.
BCS	IF C THEN PC' = PC + M	.	.	.	.	.	.
BEQ	IF Z THEN PC' = PC + M	.	.	.	.	.	.
BIT	A /\ M	M₇	X	.	.	.	M₆
BMI	IF N THEN PC' = PC + 1	.	.	.	.	.	.
BNE	IF NOT Z THEN PC' = PC + 1	.	.	.	.	.	.
BPL	IF NOT N THEN PC' = PC + 1	.	.	.	.	.	.
BRK	(100 + S--) = PC_15-8 (100 + S'--) = PC_7-0 (100 + S''--) = P PC' = (FFFE) P₄' = 1	.	.	.	.	.	.
BVC	IF NOT V THEN PC' = PC + 1	.	.	.	.	.	.
BVS	IF V THEN PC' = PC + 1	.	.	.	.	.	.
CLC	C' = 0	.	.	0	.	.	.
CLD	D' = 0	.	.	.	.	0	.
CLI	I' = 0	.	.	.	0	.	.
CLV	V' = 0	.	.	.	.	.	0
CMP	A - M	X	X	X	.	.	.
CPX	X - M	X	X	X	.	.	.
CPY	Y - M	X	X	X	.	.	.
DCP^*	M' = M - 1 A - M'	X	X	X	.	.	.
DEC	M' = M - 1	X	X	.	.	.	.
DEX	X' = X - 1	X	X	.	.	.	.
DEY	Y' = Y - 1	X	X	.	.	.	.
EOR	A' = A \^/ M	X	X	.	.	.	.
INC	M' = M + 1	X	X	.	.	.	.
INX	X' = X + 1	X	X	.	.	.	.
INY	Y' = Y + 1	X	X	.	.	.	.
ISB^*	M' = M + 1 A' = A - M' - ~C ¹	X	X	X	.	.	.
JAM^*	These instructions never finish; the CPU is locked in an infinite cycle. Coprocessors continue to function normally.
JMP	PC = M_short	.	.	.	.	.	.
JSR	(100 + S--) = (PC - 1)_15-8 (100 + S'--) = (PC - 1)_7-0 ² PC = M_short	.	.	.	.	.	.
LAS^*	A' = S /\ M S' = S /\ M X' = S /\ M	X	X	.	.	.	.
LAX^*	A' = M X' = M	X	X	.	.	.	.
LDA	A' = M	X	X	.	.	.	.
LDX	X' = M	X	X	.	.	.	.
LDY	Y' = M	X	X	.	.	.	.
LSR	M' = M >> 1	0	X	X	.	.	.
NOP	Nothing is done	.	.	.	.	.	.
ORA	A' = A \/ M	X	X	.	.	.	.
PHA	*(100 + S--) = A	.	.	.	.	.	.
PHP	*(100 + S--) = P	.	.	.	.	.	.
PLA	A' = *(100 + ++S)	X	X	.	.	.	.
PLP	P' = *(100 + ++S)	RESTORED
RLA^*	M' = (M << 1) + C A' = A /\ M'	X	X	X	.	.	.
ROL	M' = (M << 1) + C	X	X	X	.	.	.
ROR	M' = (M >> 1) + (C * 80)	X	X	X	.	.	.
RRA^*	M' = (M >> 1) + (C * 80) A' = A + M' + C' ^{1 3}	X	X	X	.	.	.
RTI	P' = (100 + ++S) PC_7-0 = (100 + ++S) ² PC_15-8 = *(100 + ++S)	RESTORED
RTS	PC_7-0' = (100 + ++S) PC_15-8' = (100 + ++S) ² PC'' = PC' + 1	.	.	.	.	.	.
SAX^*	M' = A /\ X	.	.	.	.	.	.
SBC	A' = A - M - ~C ¹	X	X	X	.	.	.
SEC	C' = 1	.	.	1	.	.	.
SED	D' = 1	.	.	.	.	1	.
SEI	I' = 1	.	.	.	1	.	.
SLO^*	M' = M << 1 A' = A \/ M'	X	X	X	.	.	.
SRE^*	M' = M >> 1 A' = A \^/ M'	X	X	X	.	.	.
STA	M' = A	.	.	.	.	.	.
STX	M' = X	.	.	.	.	.	.
STY	M' = Y	.	.	.	.	.	.
SX7^*	M' = X /\ 07	.	.	.	.	.	.
SY7^*	M' = Y /\ 07	.	.	.	.	.	.
TAX	X' = A	X	X	.	.	.	.
TAY	Y' = A	X	X	.	.	.	.
TSX	X' = S	X	X	.	.	.	.
TXA	A' = X	X	X	.	.	.	.
TXS	S' = X	.	.	.	.	.	.
TYA	A' = Y	X	X	.	.	.	.
XEA^*	A' = (A \/ EE) /\ M X' = (A \/ EE) /\ M	X	X	.	.	.	.
XS7^*	S' = A /\ X M' = S' /\ 07	.	.	.	.	.	.

Notes:

^* Undocumented instruction. The behavior of these opcodes was observed on an Atari 800. It may vary with other 6502-based CPU's.

¹ In decimal mode, N and V are set after the high-order nibble is added or subtracted but before it is decimal-corrected, according to binary rules. Z is always set according to binary mode, not decimal. When decimal-correcting a nibble for addition, 6 is added if (nibble >= A) \/ C', and C'' = C' \/ (nibble + 6 >= 10). Thus, F + F in decimal mode is 14, not 24. When decimal-correcting a nibble for subtraction, 6 is subtracted if ~C', and C'' = C' \/ (nibble - 6 < 0). Also, decimal correction can result in nibbles ranging from A-F; for example, C + D results in 19 before correction, 1F after.

² The value stored for the JSR operation is one byte prior to the address of the next instruction. However, the value stored for interrupts is the exact address of the next instruction.

³ The carry bit is used twice in this operation: once for the rotate, and then the new value is used in the addition, creating the final value.

⁴ V is set according to the function: (A₆ /\ M₆) \^/ (A₇ /\ M₇).

Atari "Sally" (6502) Instruction Set

Instruction Descriptions (listed alphabetically):

Notes:

Back to Atari Technical Information page