Difference between revisions of "65c816 Instructions"

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Revision as of 22:53, 9 November 2019

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.

  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.

  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.)

  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.

  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.

  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.

  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).

  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.

  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.

  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