LDA

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

• 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, page 462 on LDA
• Labiak, page 149 on LDA
• 2.1.1 on MCS6500 Manual, page 4 on LDA
• Carr, page 263 on LDA
• Leventhal, 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