LDA: Difference between revisions

Revision as of 01:12, 20 November 2023


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 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.

External Links

Eyes & Lichty page on LDA: https://archive.org/details/0893037893ProgrammingThe65816/page/n488
Labiak page 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 on LDA: https://archive.org/details/6502UsersManual/page/n276
Leventhal page 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

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-'''LDA''' (Load Accumulator) is a 65x instruction that loads the accumulator.  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.
+'''LDA''' (Load Accumulator) is a 65x instruction that loads the accumulator.  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 ===