65c816 Instructions

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There are approximately 91 opcodes in ASM. They are divided into different categories.

Loading instructions

These instructions load an 8-bit or a 16-bit value into one of the three registers.

Instruction Description
LDA Load into accumulator from memory
LDX Load into X from memory
LDY Load into Y from memory

Compare instructions

These instructions, usually used with branch commands, compare one of the three registers with a value or memory. (They essentially subtract the value following the compare instruction from the value in the register, affecting the processor flags but not the register itself.)

Instruction Description
CMP Compare accumulator with memory
CPY Compare Y with memory
CPX Compare X with memory

Storage instructions

These instructions store various values from a register into memory.

Instruction Description
STA Store Accumulator to Memory
STX Store X to Memory
STY Store Y to Memory
STZ Store Zero to Memory

Branching instructions

These instructions branch depending on the processor flags' status, except BRA and BRL, which always branch regardless of the processor flags.

Instruction Description
BCC Branch if Carry Clear
BCS Branch if Carry Set
BPL Branch if Plus value
BMI Branch if Minus value
BNE Branch if not Equal/Branch if not zero
BEQ Branch if Equal/Branch if zero
BVC Branch if Overflow Clear
BVS Branch if Overflow Set
BRL Branch Always Long
BRA Branch Always

Mathematical instructions

These instructions perform addition and subtraction with the registers and memory. (Note that there are no opcodes for multiplication and division; special registers must be used for those.)

Instruction Description
ADC Add with carry
SBC Subtract with Carry
INC Increment Accumulator or Memory
INX Increment X
INY Increment Y
DEC Decrement Accumulator or Memory
DEX Decrement X
DEY Decrement Y

Processor flag instructions

These instructions set or clear various processor flags of the SNES.

Instruction Description
SEP Set Processor Status Flag
REP Reset Processor Status Flag
SEC Set Carry Flag
SED Set Decimal Flag
SEI Set Interrupt Flag
CLC Clear Carry Flag
CLD Clear Decimal Flag
CLI Clear Interrupt Flag
CLV Clear Overflow Flag
XCE Exchange Carry and Emulation (swaps bits of emulation flag and carry flag, toggling emulation mode on/off)

Stack instructions

These instructions push and pull various bytes on/from the stack, a special designated area of RAM that is located at $01FF-$010B in SMW.

Instruction Description
PEA Push Effective Address (Simply push a 16-bit absolute value on the stack)
PEI Push Effective Indirect Address
PER Push Program Counter Relative
PHA Push Accumulator
PHB Push Data Bank Register
PHD Push Direct Page Register
PHK Push Program Bank Register
PHP Push Processor Status Flags
PHX Push X
PHY Push Y
PLA Pull Accumulator
PLB Pull Data Bank Register
PLD Pull Direct Page Register
PLP Pull Processor Status Flags
PLX Pull X
PLY Pull Y

Bitwise instructions

These operations affect the individual bits of A and/or memory.

Instruction Description
AND AND Accumulator with Memory
ASL Left Shift Accumulator or Memory
BIT Bit Test
EOR Exclusive OR Accumulator with Memory
LSR Shift Right Accumulator or Memory
ORA OR Accumulator with Memory
ROL Rotate Left Accumulator or Memory
ROR Rotate Right Accumulator or Memory
TRB Test and Reset Bit
TSB Test and Set Bit

Transfer instructions

These opcodes transfer values from register to register (or, in the case of MVN and MVP, from memory to memory).

Instruction Description
TAX Transfer Accumulator to X
TAY Transfer Accumulator to Y
TCD Transfer Accumulator to Direct Page
TCS Transfer Accumulator to Stack pointer
TDC Transfer Direct Page to Accumulator
TSC Transfer Stack Pointer to Accumulator
TSX Transfer Stack Pointer to X
TXA Transfer X to Accumulator
TXS Transfer X to Stack Pointer
TXY Transfer X to Y
TYA Transfer Y to Accumulator
TYX Transfer Y to X
MVN Block Move Negative
MVP Block Move Positive

Program flow instructions

These instructions jump into some other part of the ROM/RAM.

Instruction Description
JML Jump Long
JMP Jump
JSL Jump to Subroutine Long
JSR Jump to Subroutine
RTI Return from Interrupt
RTL Return from Subroutine Long
RTS Return from Subroutine

Other instructions

These are other misc. opcodes.

Instruction Description
BRK Software Break (Sets the B flag in emulation mode, interrupt in native)
COP Coprocessor Empowerment (interrupt)
NOP No operation (does absolutely nothing except waste a cycle of processing time)
STP Stop the Clock (freezes the SNES's processor)
WAI Wait for Interrupt
XBA Exchanges low and high byte of the A register