ORA

Basic Info
Addressing Mode	Opcode	Length	Speed
Immediate	09	2 bytes	2 cycles*
Absolute	0D	3 bytes	4 cycles*
Absolute Long	0F	4 bytes	5 cycles*
Direct Page	05	2 bytes	3 cycles*
Direct Page Indirect	12	2 bytes	5 cycles*
Direct Page Indirect Long	07	2 bytes	6 cycles*
absolute indexed by X	1D	3 bytes	4 cycles*
absolute long indexed by X	1F	4 bytes	5 cycles*
absolute indexed by Y	19	3 bytes	4 cycles*
direct page indexed by X	15	2 bytes	4 cycles*
direct page indexed indirect by X	01	2 bytes	6 cycles*
direct page indirect indexed by Y	11	2 bytes	5 cycles*
direct page indirect long indexed by Y	17	2 bytes	6 cycles*
Stack Relative	03	2 bytes	4 cycles*
stack relative indirect indexed by Y	13	2 bytes	7 cycles*

Flags Affected
N	V	M	X	D	I	Z	C
	.	.	.	.	.		.

ORA is a 65x instruction that performs a logical OR and stores the result in the accumulator.

Cycle Penalties

• In all addressing modes, ORA takes one extra cycle when the accumulator is 16 bits wide.
• In direct page addressing modes, ORA takes another extra cycle if the low byte of the direct page register is nonzero.

See Also

• AND
• EOR

External Links

• Eyes & Lichty page 471, on ORA: https://archive.org/details/0893037893ProgrammingThe65816/page/n497
• Labiak page 156 on ORA: https://archive.org/details/Programming_the_65816/page/n166
• MCS6500 Manual page 21 on ORA: https://archive.org/details/mos_microcomputers_programming_manual/page/n36
• Carr page 266 on ORA: https://archive.org/details/6502UsersManual/page/n279
• Leventhal page 3-79 on ORA: https://archive.org/details/6502-assembly-language-programming/page/n128
• snes9x implementation of ORA: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L917
• undisbeliever on ORA: https://undisbeliever.net/snesdev/65816-opcodes.html#ora-or-accumulator-with-memory