STA: Difference between revisions

Latest revision as of 04:23, 6 December 2023


Basic Info
Addressing Mode	Opcode	Length	Speed
Absolute	8D	3 bytes	4 cycles*
Absolute Long	8F	4 bytes	5 cycles*
Direct Page	85	2 bytes	3 cycles*
Direct Page Indirect	92	2 bytes	5 cycles*
Direct Page Indirect Long	87	2 bytes	6 cycles*
absolute indexed by X	9D	3 bytes	4 cycles*
absolute long indexed by X	9F	4 bytes	5 cycles*
absolute indexed by Y	99	3 bytes	4 cycles*
direct page indexed by X	95	2 bytes	4 cycles*
direct page indexed indirect by X	81	2 bytes	6 cycles*
direct page indirect indexed by Y	91	2 bytes	5 cycles*
direct page indirect long indexed by Y	97	2 bytes	6 cycles*
Stack Relative	83	2 bytes	4 cycles*
stack relative indirect indexed by Y	93	2 bytes	7 cycles*


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

STA (Store Accumulator) is a 65x instruction that stores the value of the accumulator. If the accumulator is 16 bits wide, its low byte is stored at the effective address and its high byte is stored at the effective address plus one.

Cycle Penalties

In all addressing modes, STA takes one extra cycle when the accumulator is 16 bits wide.
In direct page addressing modes, STA takes another extra cycle if the low byte of the direct page register is nonzero.

External Links

Eyes & Lichty page 503, on STA: https://archive.org/details/0893037893ProgrammingThe65816/page/n529
Labiak page 184 on STA: https://archive.org/details/Programming_the_65816/page/n194
MCS6500 Manual page 5 on STA: https://archive.org/details/mos_microcomputers_programming_manual/page/n20
Carr page 273 on STA: https://archive.org/details/6502UsersManual/page/n286
Leventhal page 3-96 on STA: https://archive.org/details/6502-assembly-language-programming/page/n145
snes9x implementation of STA: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L1219
undisbeliever on STA: https://undisbeliever.net/snesdev/65816-opcodes.html#sta-store-accumulator-to-memory

@@ Line 1: / Line 1: @@
-'''STA''' (Store Accumulator) is a 65x instruction that stores the value of the [[accumulator]].
+{| class="wikitable" style="float:right;clear:right;width:40%"
+!colspan="8"|Basic Info
+|+
+|'''Addressing Mode'''
+|'''Opcode'''
+|'''Length'''
+|'''Speed'''
+|+
+|[[Absolute]]
+|8D
+|3 bytes
+|4 cycles*
+|+
+|[[Absolute Long]]
+|8F
+|4 bytes
+|5 cycles*
+|+
+|[[Direct Page Addressing|Direct Page]]
+|85
+|2 bytes
+|3 cycles*
+|+
+|[[Direct Page Indirect]]
+|92
+|2 bytes
+|5 cycles*
+|+
+|[[Direct Page Indirect Long]]
+|87
+|2 bytes
+|6 cycles*
+|+
+|absolute indexed by X
+|9D
+|3 bytes
+|4 cycles*
+|+
+|absolute long indexed by X
+|9F
+|4 bytes
+|5 cycles*
+|+
+|absolute indexed by Y
+|99
+|3 bytes
+|4 cycles*
+|+
+|direct page indexed by X
+|95
+|2 bytes
+|4 cycles*
+|+
+|direct page indexed indirect by X
+|81
+|2 bytes
+|6 cycles*
+|+
+|direct page indirect indexed by Y
+|91
+|2 bytes
+|5 cycles*
+|+
+|direct page indirect long indexed by Y
+|97
+|2 bytes
+|6 cycles*
+|+
+|[[Stack Relative]]
+|83
+|2 bytes
+|4 cycles*
+|+
+|stack relative indirect indexed by Y
+|93
+|2 bytes
+|7 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 22: / Line 99: @@
 |.
 |}
+'''STA''' (Store Accumulator) is a 65x instruction that stores the value of the [[accumulator]].  If the accumulator is 16 bits wide, its low byte is stored at the effective address and its high byte is stored at the effective address plus one.
+===== Cycle Penalties =====
+* In all [[addressing modes]], STA takes one extra cycle when the accumulator is 16 bits wide.
+* In [[direct page addressing]] modes, STA takes another extra cycle if the low byte of the [[direct page register]] is nonzero.
 === See Also ===
+* [[LDA]]
 * [[STX]]
 * [[STY]]
 * [[STZ]]
+=== External Links ===
+* [[Eyes & Lichty]] page 503, on STA: https://archive.org/details/0893037893ProgrammingThe65816/page/n529
+* [[Labiak]] page 184 on STA: https://archive.org/details/Programming_the_65816/page/n194
+* [[MCS6500 Manual]] page 5 on STA: https://archive.org/details/mos_microcomputers_programming_manual/page/n20
+* [[Carr]] page 273 on STA: https://archive.org/details/6502UsersManual/page/n286
+* [[Leventhal]] page 3-96 on STA: https://archive.org/details/6502-assembly-language-programming/page/n145
+* snes9x implementation of STA: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L1219
+* undisbeliever on STA: https://undisbeliever.net/snesdev/65816-opcodes.html#sta-store-accumulator-to-memory
 [[Category:ASM]]
 [[Category:Group One Instructions]]
+[[Category:Inherited from 6502]]
+[[Category:Load/Store Instructions]]