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WDM: Difference between revisions
From SnesLab
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!colspan="8"|Flags | !colspan="8"|Flags Affected | ||
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|V | |[[V Flag|V]] | ||
|M | |[[M Flag|M]] | ||
|X | |[[X Flag|X]] | ||
|D | |[[D Flag|D]] | ||
|I | |[[I Flag|I]] | ||
|Z | |[[Z Flag|Z]] | ||
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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]]. | ||
=== Trivia === | === Trivia === | ||
The [[Labiak]] textbook does not describe the WDM instruction. | * 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 === | === See Also === | ||
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=== External Links === | === 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 | |||
[[Category: ASM]] | [[Category: ASM]] | ||
[[Category:65c816 additions]] | [[Category:65c816 additions]] | ||
[[Category:Two-byte Instructions]] | |||
[[Category:Implied Instructions]] | |||
[[Category:Two-cycle Instructions]] | |||
Latest revision as of 11:39, 14 December 2023
| 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.
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