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'''LDA''' (Load Accumulator) is a 65x instruction that loads the accumulator.
{| class="wikitable" style="float:right;clear:right;width:50%"
 
{| class="wikitable" style="float:right;clear:right;width:30%"
!colspan="8"|Basic Info
!colspan="8"|Basic Info
|+
|+
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|'''Speed'''
|'''Speed'''
|+
|+
|immediate
|[[Immediate]]
|A9
|A9
|2 bytes
|2/3 bytes
|2 cycles
|2 cycles*
|+
|+
|absolute
|[[Absolute]]
|AD
|AD
|3 bytes
|3 bytes
|4 cycles
|4 cycles*
|+
|+
|absolute long
|[[Absolute Long]]
|AF
|AF
|4 bytes
|4 bytes
|5 cycles
|5 cycles*
|+
|+
|direct page
|[[Direct Page Addressing|Direct Page]]
|A5
|A5
|2 bytes
|2 bytes
|3 cycles
|3 cycles*
|+
|+
|direct page indirect
|[[Direct Page Indirect]]
|B2
|B2
|2 bytes
|2 bytes
|5 cycles
|5 cycles*
|+
|+
|direct page indirect long
|[[Direct Page Indirect Long]]
|A7
|A7
|2 bytes
|2 bytes
|6 cycles
|6 cycles*
|+
|+
|absolute indexed by X
|[[Absolute Indexed by X]]
|BD
|BD
|3 bytes
|3 bytes
|4 cycles
|4 cycles*
|+
|+
|absolute long indexed by X
|[[Absolute Long Indexed by X]]
|BF
|BF
|4 bytes
|4 bytes
|5 cycles
|5 cycles*
|+
|+
|absolute indexed by Y
|[[Absolute Indexed by Y]]
|B9
|B9
|3 bytes
|3 bytes
|4 cycles
|4 cycles*
|+
|+
|direct page indexed by X
|[[Direct Page Indexed by X]]
|B5
|B5
|2 bytes
|2 bytes
|4 cycles
|4 cycles*
|+
|+
|direct page indexed indirect by X
|[[Direct Page Indexed Indirect by X]]
|A1
|A1
|2 bytes
|2 bytes
|6 cycles
|6 cycles*
|+
|+
|direct page indirect indexed by Y
|[[Direct Page Indirect Indexed by Y]]
|B1
|B1
|2 bytes
|2 bytes
|5 cycles
|5 cycles*
|+
|+
|direct page indirect long indexed by Y
|[[Direct Page Indirect Long Indexed by Y]]
|B7
|B7
|2 bytes
|2 bytes
|6 cycles
|6 cycles*
|+
|+
|stack relative
|[[Stack Relative]]
|A3
|A3
|2 bytes
|2 bytes
|4 cycles
|4 cycles*
|+
|+
|stack relative indirect indexed by Y
|[[Stack Relative Indirect Indexed by Y]]
|B3
|B3
|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
|+
|[[Negative Flag|N]]
|[[Overflow Flag|V]]
|[[M Flag|M]]
|[[X Flag|X]]
|[[Decimal Flag|D]]
|[[I Flag|I]]
|[[Zero Flag|Z]]
|[[Carry Flag|C]]
|+
|+
|N
|N
|V
|M
|X
|D
|I
|Z
|C
|+
|
|.
|.
|.
|.
|.
|.
|.
|.
|
|.
|.
|Z
|.
|.
|}
|}
'''LDA''' (LoaD Accumulator) is a 65x instruction that loads a value into the accumulator.  In [[immediate addressing]] only, LDA is a total of 3 bytes long when the accumulator is 16 bits wide.
==== Syntax ====
<pre>
LDA #const
LDA addr
LDA long
LDA dp
LDA (dp)
LDA [dp]
LDA addr, X
LDA long, X
LDA addr, Y
LDA dp, X
LDA (dp, X)
LDA (dp), Y
LDA [dp], Y
LDA sr, S
LDA (sr, S), Y
</pre>
If you want to load zero into the [[accumulator]], [[TDC]] may be a better choice, but only if the [[direct page register]] is zero.
==== Cycle Penalties ====
* In all [[addressing modes]], LDA takes one extra cycle when the accumulator is 16 bits wide.
* In [[direct page addressing]] modes, LDA takes another extra cycle if the low byte of the [[direct page register]] is nonzero.
* In both the [[Absolute Indexed]] and the DP Indirect Indexed by Y admodes, LDA takes an extra cycle if adding the index crosses a page boundary.
=== See Also ===
* [[STA]]
* [[LDX]]
* [[LDY]]
=== External Links ===
* [[Eyes & Lichty]], [https://archive.org/details/0893037893ProgrammingThe65816/page/462 page 462] on LDA
* [[Labiak]], [https://archive.org/details/Programming_the_65816/page/n159 page 149] on LDA
* 2.1.1 on [[MCS6500 Manual]], [https://archive.org/details/mos_microcomputers_programming_manual/page/n19 page 4] on LDA
* [[Carr]], [https://archive.org/details/6502UsersManual/page/n276 page 263] on LDA
* [[Leventhal]], [https://archive.org/details/6502-assembly-language-programming/page/n120 page 3-71] on LDA
* snes9x implementation of LDA: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L678
* undisbeliever on LDA: https://undisbeliever.net/snesdev/65816-opcodes.html#lda-load-accumulator-from-memory
* Pickens, John. http://www.6502.org/tutorials/6502opcodes.html#LDA


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

Latest revision as of 06:36, 22 August 2024

Basic Info
Addressing Mode Opcode Length Speed
Immediate A9 2/3 bytes 2 cycles*
Absolute AD 3 bytes 4 cycles*
Absolute Long AF 4 bytes 5 cycles*
Direct Page A5 2 bytes 3 cycles*
Direct Page Indirect B2 2 bytes 5 cycles*
Direct Page Indirect Long A7 2 bytes 6 cycles*
Absolute Indexed by X BD 3 bytes 4 cycles*
Absolute Long Indexed by X BF 4 bytes 5 cycles*
Absolute Indexed by Y B9 3 bytes 4 cycles*
Direct Page Indexed by X B5 2 bytes 4 cycles*
Direct Page Indexed Indirect by X A1 2 bytes 6 cycles*
Direct Page Indirect Indexed by Y B1 2 bytes 5 cycles*
Direct Page Indirect Long Indexed by Y B7 2 bytes 6 cycles*
Stack Relative A3 2 bytes 4 cycles*
Stack Relative Indirect Indexed by Y B3 2 bytes 7 cycles*
Flags Affected
N V M X D I Z C
N . . . . . Z .

LDA (LoaD Accumulator) is a 65x instruction that loads a value into the accumulator. In immediate addressing only, LDA is a total of 3 bytes long when the accumulator is 16 bits wide.

Syntax

LDA #const
LDA addr
LDA long
LDA dp
LDA (dp)
LDA [dp]
LDA addr, X
LDA long, X
LDA addr, Y
LDA dp, X
LDA (dp, X)
LDA (dp), Y
LDA [dp], Y
LDA sr, S
LDA (sr, S), Y

If you want to load zero into the accumulator, TDC may be a better choice, but only if the direct page register is zero.

Cycle Penalties

See Also

External Links

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