WDM: Difference between revisions

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.

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

@@ Line 1: / Line 1: @@
-'''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]].
+{| class="wikitable" style="float:right;clear:right;width:40%"
-{| class="wikitable" style="float:right;clear:right;width:30%"
 !colspan="8"|Basic Info
 |+
@@ Line 9: / Line 7: @@
 |'''Speed'''
 |+
-|
+|[[Implied]] (type 3)<sup>[4]</sup>
 |42
 |2 byte
@@ Line 16: / Line 14: @@
 {| class="wikitable" style="float:right;clear:right;width:30%"
-!colspan="8"|Flags Clobbered
+!colspan="8"|Flags Affected
 |+
-|N
+|[[N Flag|N]]
-|V
+|[[V Flag|V]]
-|M
+|[[M Flag|M]]
-|X
+|[[X Flag|X]]
-|D
+|[[D Flag|D]]
-|I
+|[[I Flag|I]]
-|Z
+|[[Z Flag|Z]]
-|C
+|[[C Flag|C]]
 |+
 |.
@@ Line 36: / Line 34: @@
 |.
 |}
+'''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 ===
+* 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 ===
+* [[COP]]
+* [[BRK]]
+=== 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:65c816 additions]]
+[[Category:Two-byte Instructions]]
+[[Category:Implied Instructions]]
+[[Category:Two-cycle Instructions]]