65c816 Instructions
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 two cycles 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 |