STZ: Difference between revisions

Latest revision as of 13:52, 14 December 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. The size of the accumulator determines how many zero bytes are written.

Cycle Penalties

STZ takes one additional cycle if the accumulator is 16 bits wide, in all addressing modes.
In direct page addressing modes only, STZ takes another additional cycle if the low byte of the direct page register is nonzero.

External Links

Eyes & Lichty page 507, on STZ: https://archive.org/details/0893037893ProgrammingThe65816/page/n533
"Storing Zero to Memory," page 103, lbid. https://archive.org/details/0893037893ProgrammingThe65816/page/n129
Labiak page 188 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 1: / Line 1: @@
-'''STZ''' (Store Zero) is a [[65c816]] instruction that zeros out memory.
+{| class="wikitable" style="float:right;clear:right;width:40%"
-{| class="wikitable" style="width:30%"
 !colspan="8"|Basic Info
 |+
@@ Line 9: / Line 7: @@
 |'''Speed'''
 |+
-|absolute
+|[[Absolute]]
 |9C
 |3 bytes
-|4 cycles
+|4 cycles*
 |+
-|direct page
+|[[Direct Page Addressing|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*
 |}
 {| class="wikitable" style="float:right;clear:right;width:30%"
-!colspan="9"|Flags Clobbered
+!colspan="9"|Flags Affected
 |+
-|N
+|[[Negative Flag|N]]
-|V
+|[[Overflow Flag|V]]
-|M
+|[[M Flag|M]]
-|X
+|[[X Flag|X]]
-|D
+|[[Decimal Flag|D]]
-|I
+|[[I Flag|I]]
-|Z
+|[[Zero Flag|Z]]
-|C
+|[[Carry Flag|C]]
 |+
 |.
@@ Line 51: / Line 49: @@
 |.
 |}
+'''STZ''' (Store Zero) is a [[65c816]] instruction that zeros out memory.  The size of the [[accumulator]] determines how many zero bytes are written.
+===== Cycle Penalties =====
+* STZ takes one additional cycle if the accumulator is 16 bits wide, in all [[addressing modes]].
+* In [[direct page addressing]] modes only, STZ takes another additional cycle if the low byte of the [[direct page register]] is nonzero.
 === See Also ===
@@ Line 58: / Line 62: @@
 === External Links ===
-* [[Eyes & Lichty]] page on STZ: https://archive.org/details/0893037893ProgrammingThe65816/page/n533
+* [[Eyes & Lichty]] page 507, on STZ: https://archive.org/details/0893037893ProgrammingThe65816/page/n533
-* [[Labiak]] page on STZ: https://archive.org/details/Programming_the_65816/page/n198
+* "Storing Zero to Memory," page 103, lbid. https://archive.org/details/0893037893ProgrammingThe65816/page/n129
+* [[Labiak]] page 188 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
 [[Category:ASM]]
 [[Category:65c02 additions]]
+[[Category:Load/Store Instructions]]