LDA

Basic Info
Addressing Mode	Opcode	Length	Speed
Immediate	A9	2 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
	.	.	.	.	.		.

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

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: https://archive.org/details/0893037893ProgrammingThe65816/page/n488
• Labiak page 149 on LDA: https://archive.org/details/Programming_the_65816/page/n159
• MCS6500 Manual page on LDA: https://archive.org/details/mos_microcomputers_programming_manual/page/n19
• Carr page 263 on LDA: https://archive.org/details/6502UsersManual/page/n276
• Leventhal page 3-71 on LDA: https://archive.org/details/6502-assembly-language-programming/page/n120
• 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