Accumulator Addressing

There are six instructions that support Accumulator Addressing on the 65c816. They are:

• ASL (opcode 0A)
• DEC (opcode 3A)
• INC (opcode 1A)
• LSR (opcode 4A)
• ROL (opcode 2A)
• ROR (opcode 6A)

They all are one byte long. None of them write to external memory. They are all read-modify-write instructions.

In this admode, the accumulator is the operand.^[3] In native mode when the m flag is clear, the accumulator is 16 bits wide. Otherwise it is 8 bit (when m is set or in emulation mode).

Syntax

ROR
RORA
ROR A

Interestingly, XBA is not considered to use accumulator addressing. But XCN on the SPC700 is.

See Also

• Implied Addressing
• Immediate Addressing

References

1. Eyes & Lichty, page 387: https://archive.org/details/0893037893ProgrammingThe65816/page/387
2. page 126, lbid: https://archive.org/details/0893037893ProgrammingThe65816/page/126
3. section 3.5.8 of 65c816 datasheet, https://westerndesigncenter.com/wdc/documentation/w65c816s.pdf
4. Clark, Bruce. http://www.6502.org/tutorials/65c816opcodes.html#5.6