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'''STA''' (Store Accumulator) is a 65x instruction that stores the value of the [[accumulator]].
{| class="wikitable" style="float:right;clear:right;width:40%"
 
{| class="wikitable" style="float:right;clear:right;width:30%"
!colspan="8"|Basic Info
!colspan="8"|Basic Info
|+
|+
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|'''Speed'''
|'''Speed'''
|+
|+
|absolute
|[[Absolute]]
|8D
|8D
|3 bytes
|3 bytes
|4 cycles
|4 cycles*
|+
|+
|absolute long
|[[Absolute Long]]
|8F
|8F
|4 bytes
|4 bytes
|5 cycles
|5 cycles*
|+
|+
|direct page
|[[Direct Page Addressing|Direct Page]]
|85
|85
|2 bytes
|2 bytes
|3 cycles
|3 cycles*
|+
|+
|direct page indirect
|[[Direct Page Indirect]]
|92
|92
|2 bytes
|2 bytes
|5 cycles
|5 cycles*
|+
|+
|direct page indirect long
|[[Direct Page Indirect Long]]
|87
|87
|2 bytes
|2 bytes
|6 cycles
|6 cycles*
|+
|+
|absolute indexed by X
|[[Absolute Indexed by X]]
|9D
|9D
|3 bytes
|3 bytes
|4 cycles
|4 cycles*
|+
|+
|absolute long indexed by X
|[[Absolute Long Indexed by X]]
|9F
|9F
|4 bytes
|4 bytes
|5 cycles
|5 cycles*
|+
|+
|absolute indexed by Y
|[[Absolute Indexed by Y]]
|99
|99
|3 bytes
|3 bytes
|4 cycles
|4 cycles*
|+
|+
|direct page indexed by X
|[[Direct Page Indexed by X]]
|95
|95
|2 bytes
|2 bytes
|4 cycles
|4 cycles*
|+
|+
|direct page indexed indirect by X
|[[Direct Page Indexed Indirect by X]]
|81
|81
|2 bytes
|2 bytes
|6 cycles
|6 cycles*
|+
|+
|direct page indirect indexed by Y
|[[Direct Page Indirect Indexed by Y]]
|91
|91
|2 bytes
|2 bytes
|5 cycles
|5 cycles*
|+
|+
|direct page indirect long indexed by Y
|[[Direct Page Indirect Long Indexed by Y]]
|97
|97
|2 bytes
|2 bytes
|6 cycles
|6 cycles*
|+
|+
|stack relative
|[[Stack Relative]]
|83
|83
|2 bytes
|2 bytes
|4 cycles
|4 cycles*
|+
|+
|stack relative indirect indexed by Y
|[[Stack Relative Indirect Indexed by Y]]
|93
|93
|2 bytes
|2 bytes
|7 cycles
|7 cycles*
|}
|}


{| class="wikitable" style="float:right;clear:right;width:30%"
{| 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]]
|+
|+
|.
|.
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|.
|.
|}
|}
'''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.
No flags are affected.
==== Syntax ====
<pre>
STA addr
STA long
STA dp
STA (dp)
STA [dp]
STA addr, X
STA long, X
STA addr, Y
STA dp, X
STA (dp, X)
STA (dp), Y
STA [dp], Y
STA sr, S
STA (sr, S), Y
</pre>
If you are trying to store zero somewhere, consider [[STZ]] instead.
==== 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 ===
=== See Also ===
* [[LDA]]
* [[STX]]
* [[STX]]
* [[STY]]
* [[STY]]
* [[STZ]]
 
=== External Links ===
* [[Eyes & Lichty]], [https://archive.org/details/0893037893ProgrammingThe65816/page/503 page 503] on STA
* [[Labiak]], [https://archive.org/details/Programming_the_65816/page/n194 page 184] on STA
* 2.1.2 on [[MCS6500 Manual]], [https://archive.org/details/mos_microcomputers_programming_manual/page/n20 page 5] on STA
* [[Carr]], [https://archive.org/details/6502UsersManual/page/n286 page 273] on STA
* [[Leventhal]], [https://archive.org/details/6502-assembly-language-programming/page/n145 page 3-96] on STA
* 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
* Pickens, John. http://www.6502.org/tutorials/6502opcodes.html#STA


[[Category:ASM]]
[[Category:ASM]]
[[Category:Group One Instructions]]
[[Category:Group One Instructions]]
[[Category:Inherited from 6502]]
[[Category:Inherited from 6502]]
[[Category:Load/Store Instructions]]

Latest revision as of 06:37, 22 August 2024

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.

No flags are affected.

Syntax

STA addr
STA long
STA dp
STA (dp)
STA [dp]
STA addr, X
STA long, X
STA addr, Y
STA dp, X
STA (dp, X)
STA (dp), Y
STA [dp], Y
STA sr, S
STA (sr, S), Y

If you are trying to store zero somewhere, consider STZ instead.

Cycle Penalties

See Also

External Links

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