CPY: Difference between revisions

Revision as of 02:14, 19 December 2023


Basic Info
Addressing Mode	Opcode	Length	Speed
Immediate	C0	2 bytes*	2 cycles*
Absolute	CC	3 bytes	4 cycles*
Direct Page	C4	2 bytes	3 cycles*


Flags Affected
N	V	M	X	D	I	Z	C
	.	.	.	.	.

CPY (Compare Y) is a 65x instruction that compares the value of the Y index register. Internally, this is done via a subtraction, but the difference is not stored anywhere.

External Links

Eyes & Lichty page 450, on CPY: https://archive.org/details/0893037893ProgrammingThe65816/page/n476
Labiak page 137 on CPY: https://archive.org/details/Programming_the_65816/page/n147
MCS6500 Manual page 99 on CPY: https://archive.org/details/mos_microcomputers_programming_manual/page/n117
Carr page 257 on CPY: https://archive.org/details/6502UsersManual/page/n270
Leventhal page 3-59 on CPY: https://archive.org/details/6502-assembly-language-programming/page/n108
snes9x implementation of CPY: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L442
undisbeliever on CPY: https://undisbeliever.net/snesdev/65816-opcodes.html#cpy-compare-index-register-y-with-memory

@@ Line 45: / Line 45: @@
 |}
-'''CPY''' (Compare Y) is a 65x instruction that compares the value of the [[Y index register]].
+'''CPY''' (Compare Y) is a 65x instruction that compares the value of the [[Y index register]].  Internally, this is done via a subtraction, but the difference is not stored anywhere.
 === See Also ===