STZ: Difference between revisions

Revision as of 21:49, 19 November 2023


Basic Info
Addressing Mode	Opcode	Length	Speed
absolute	9C	3 bytes	4 cycles*
direct page	64	2 bytes	3 cycles*
absolute indexed X	9E	3 bytes	5 cycles*
direct page indexed X	74	2 bytes	4 cycles*


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

STZ (Store Zero) is a 65c816 instruction that zeros out memory. STZ takes one additional cycle if the accumulator is 16 bits wide. STZ takes another additional cycle if the low byte of the direct page register is nonzero.

External Links

Eyes & Lichty page on STZ: https://archive.org/details/0893037893ProgrammingThe65816/page/n533
Labiak page on STZ: https://archive.org/details/Programming_the_65816/page/n198
snes9x implementation of STZ: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L1317
undisbeliever on STZ: https://undisbeliever.net/snesdev/65816-opcodes.html#stz-store-zero-to-memory

@@ Line 10: / Line 10: @@
 |9C
 |3 bytes
-|4 cycles
+|4 cycles*
 |+
 |direct page
 |64
 |2 bytes
-|3 cycles
+|3 cycles*
 |+
 |absolute indexed X
 |9E
 |3 bytes
-|5 cycles
+|5 cycles*
 |+
 |direct page indexed X
 |74
 |2 bytes
-|4 cycles
+|4 cycles*
 |}
@@ Line 50: / Line 50: @@
 |}
-'''STZ''' (Store Zero) is a [[65c816]] instruction that zeros out memory.
+'''STZ''' (Store Zero) is a [[65c816]] instruction that zeros out memory.  STZ takes one additional cycle if the accumulator is 16 bits wide.  STZ takes another additional cycle if the low byte of the [[direct page register]] is nonzero.
 === See Also ===