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WDM: Difference between revisions
From SnesLab
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'''WDM''' (the initials of [https://themenschfoundation.org/who-is-william-d-mensch-jr-aka-bill-mensch/ William David Mensch], the designer of the [[65c816]]) is an instruction that reserves its [[signature byte]] for future expansion of the instruction set. None of these extra 256 opcodes were ever implemented, so WDM functions essentially as a two-byte [[NOP]]. | '''WDM''' (the initials of [https://themenschfoundation.org/who-is-william-d-mensch-jr-aka-bill-mensch/ William David Mensch], the designer of the [[65c816]]) is an instruction that reserves its [[signature byte]] for future expansion of the instruction set. None of these extra 256 opcodes were ever implemented, so WDM functions essentially as a two-byte [[NOP]]. | ||
No flags are affected, but future expanded WDM opcodes may. | |||
=== Trivia === | === Trivia === | ||
Revision as of 22:07, 27 June 2024
| Basic Info | |||||||
|---|---|---|---|---|---|---|---|
| Addressing Mode | Opcode | Length | Speed | ||||
| Implied (type 3)[4] | 42 | 2 byte | 2 cycles | ||||
| Flags Affected | |||||||
|---|---|---|---|---|---|---|---|
| N | V | M | X | D | I | Z | C |
| . | . | . | . | . | . | . | . |
WDM (the initials of William David Mensch, the designer of the 65c816) is an instruction that reserves its signature byte for future expansion of the instruction set. None of these extra 256 opcodes were ever implemented, so WDM functions essentially as a two-byte NOP.
No flags are affected, but future expanded WDM opcodes may.
Trivia
- WDM is the only implied addressing instruction that is more than one byte long
- The Labiak textbook does not describe the WDM instruction.
See Also
External Links
- Eyes & Lichty page 523, on WDM: https://archive.org/details/0893037893ProgrammingThe65816/page/n549
- snes9x implementation of WDM: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L3335
- undisbeliever on WDM: https://undisbeliever.net/snesdev/65816-opcodes.html#wdm-reserved-for-future-expansion
- Table 5-4 Opcode Matrix of official 65c816 datasheet