Super NES Programming/65c816 reference

Internal Registers

Register	Description

A	The accumulator. This is the math register. It stores one of two operands or the result of most arithmetic and logical operations.
X, Y	The index registers. These can be used to reference memory, to pass data to memory, or as counters for loops.
S	The stack pointer, points to the next available(unused) location on the stack.
DBR	Data bank register, holds the default bank for memory transfers.
D	Direct page register, used for direct page addressing modes.
PBR	Program Bank, holds the bank address of all instruction fetches.
P	Processor Status, holds various important flags, see below.

Mnemonic	Value	Binary Value	Description

N	#$80	10000000	Negative	Condition codes used for branch instructions.
V	#$40	01000000	Overflow
Z	#$02	00000010	Zero
C	#$01	00000001	Carry

D	#$08	00001000	Decimal
I	#$04	00000100	IRQ disable
X	#$10	00010000	Index register size (native mode only) (0 = 16-bit, 1 = 8-bit)
M	#$20	00100000	Accumulator register size (native mode only) (0 = 16-bit, 1 = 8-bit)
E	not in P		6502 emulation mode
B	#$10	00010000	Break (emulation mode only)

Instruction	Description	Arguments	Flags set

ADC	Add A with something and carry bit. Result is put in A.	Immediate value or address	n,v,z,c	Arithmetic instructions
SBC	Subtract something and the carry bit.		n,v,z,c	Arithmetic instructions

AND	AND A with memory, storing result in A.	Immediate value or address	n,z	Logical instructions
EOR	Exclusive or		n,z
ORA	OR A with memory, storing result in A.	Immediate value or address	n,z
TSB	Test and set bits		z
TRB	Test and reset bits		z

ASL	Arithmetic shift left	A or address	c	Shift instructions
LSR	Logical shift right	A or address	c
ROL	Rotate left	A or address	c
ROR	Rotate right	A or address	c

BIT	test bits, setting	immediate value or address	n,v,z (only z if in immediate mode)	Test instructions
CMP	Compare accumulator with memory		n,z,c
CPX	Compare register X with memory		n,z,c
CPY	Compare register Y with memory		n,z,c

DEA	Decrement Accumulator		n,z
DEC	Decrement, see INC		n,z
DEX	Decrement X register		n,z
DEY	Decrement Y register		n,z
INA	Increment Accumulator		n,z
INC	Increment, see DEC		n,z
INX	Increment X register		n,z
INY	Increment Y register		n,z

NOP	No operation		none
XBA	Exchange bytes of accumulator		n,z

Instruction	Description

LDA	Load accumulator from memory
LDX	Load register X from memory
LDY	Load register Y from memory
STA	Store accumulator in memory
STX	Store register X in memory
STY	Store register Y in memory
STZ	Store zero in memory

Instruction	Description	Flags affected

TAX	Transfer Accumulator to index register X	n,z
TAY	Transfer Accumulator to index register Y	n,z
TCD	Transfer 16-bit Accumulator to Direct Page register	n,z
TCS	Transfer 16-bit Accumulator to Stack Pointer	none
TDC	Transfer Direct Page register to 16-bit Accumulator	n,z
TSC	Transfer Stack Pointer to 16-bit Accumulator	n,z
TSX	Transfer Stack Pointer to index register X	n,z
TSY _{(non-existent)}	Transfer Stack Pointer to index register Y	n,z
TXA	Transfer index register X to Accumulator	n,z
TXS	Transfer index register X to Stack Pointer	none
TXY	Transfer index register X to index register Y	n,z
TYA	Transfer index register Y to Accumulator	n,z
TYX	Transfer index register Y to index register X	n,z

Instruction	Description

BCC	Branch if Carry flag is clear (C=0)
BCS	Branch if Carry flag is set (C=1)
BNE	Branch if not equal (Z=0)
BEQ	Branch if equal (Z=1)
BPL	Branch if plus (N=0)
BMI	Branch if minus (N=1)
BVC	Branch if overflow flag is clear (V=0)
BVS	Branch if overflow flag is set (V=1)
BRA	Branch Always (unconditional)
BRL	Branch Always Long (unconditional)

Instruction	Description

JMP	Jump
JML	Jump long
JSR	Jump and save return address
JSL	Jump long and save return address
RTS	Return from subroutine
RTL	Return long from subroutine

Instruction	Description

BRK	Generate software interrupt
COP	Generate coprocessor interrupt
RTI	Return from interrupt
STP	Stop processor until RESET
WAI	Wait for hardware interrupt

Instruction	Description

CLC	Clear carry flag
CLD	Select binary arithmetic
CLI	Enable interrupt requests
CLV	Clear overflow flag
REP	Reset status bits (for example REP #%00100000 clears the M flag)
SEC	Set carry flag
SED	Select decimal arithmetic
SEP	Set status bits (for example SEP #%00010000 sets the X flag)
SEI	Disable interrupt requests
XCE	Exchange carry flag with emulation flag

Instruction	Description

PHA	Push Accumulator	Push instructions
PHX	Push index register X
PHY	Push index register Y
PHD	Push direct page register
PHB	Push data bank register
PHK	Push Program Bank Register
PHP	Push processor status
PEA	Push effective address
PEI	Push effective indirect address
PER	Push effective relative address

PLA	Pull Accumulator	Pull instructions
PLX	Pull index register X
PLY	Pull index register Y
PLP	Pull processor status
PLD	Pull direct page register
PLB	Pull data bank register


Mode	Example
Implied	PHB
Immediate[MemoryFlag]	AND #1 or 2 bytes
Immediate[IndexFlag]	LDX #1 or 2 bytes
Immediate[8-Bit]	SEP #byte
Relative	BEQ byte (signed)
Relative long	BRL 2bytes (signed)
Direct	AND byte
Direct indexed (with X)	AND byte, x
Direct indexed (with Y)	AND byte, y
Direct indirect	AND (byte)
Direct indexed indirect	AND (byte, x)
Direct indirect indexed	AND (byte), y
Direct indirect long	AND [byte]
Direct indirect indexed long	AND [byte], y
Absolute	AND 2bytes
Absolute indexed (with X)	AND 2bytes, x
Absolute indexed (with Y)	AND 2bytes, y
Absolute long	AND 3bytes
Absolute indexed long	AND 3bytes, x
Stack relative	AND byte, s
Stack relative indirect indexed	AND (byte, s), y
Absolute indirect	JMP (2bytes)
Absolute indirect long	JML [3bytes]
Absolute indexed indirect	JMP/JSR (2bytes,x)
Implied accumulator	INC
Block move	MVN/MVP byte, byte

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