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. 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 on ORA: https://archive.org/details/0893037893ProgrammingThe65816/page/n497
• Labiak page on ORA: https://archive.org/details/Programming_the_65816/page/n166
• MCS6500 Manual page on ORA: https://archive.org/details/mos_microcomputers_programming_manual/page/n36
• Carr page on ORA: https://archive.org/details/6502UsersManual/page/n279
• Leventhal page 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