ORA (OR Accumulator with Memory)¶

A = A OR [operand]

ORA performs a bitwise OR operation on the accumulator register (A) and an operand. The result is then stored in the accumulator.

Addressing Modes¶

Addressing Mode	Opcode	Bytes	Cycles
Immediate	ORA #const	`09 nn`	2
ZeroPage	ORA zp	`05 nn`	3
ZeroPage+X	ORA zp,x	`15 nn`	4
Absolute	ORA addr	`0D ll hh`	4
Absolute+X	ORA addr,x	`1D ll hh`	4-5
Absolute+Y	ORA addr,y	`19 ll hh`	4-5
(Indirect+X)	ORA (zp,x)	`01 nn`	6
(Indirect)+Y	ORA (zp),y	`11 nn`	5-6

* Add 1 cycle if page boundary is crossed.

N (Negative) – Set if the result has the most significant bit set (i.e., is negative); otherwise, it is cleared.
Z (Zero) – Set if the result is zero; otherwise, it is cleared.

; Sets A to 0x34
LDA #$10
ORA #$24

; Sets A to 0x3F
LDA #$B0
ORA #$8F

; Sets A to 0xFF
LDA #$00
ORA #$FF