ORA

Or Memory With Accumulator

Opcode: ORA Operation: A | M → A Status Register:

ORA (Or Memory With Accumulator) performs a logical OR on the operand and the accumulator and stores the result in the accumulator. This opcode is similar in function to AND and EOR.

Operation

This pseudo C code shows how the ORA opcode functions when it is executed.

Operand |= ACCUMULATOR        // OR the two values together.
SET_NEGATIVE(Operand);        // Clears the Negative Flag if the Operand is $#00-7F, otherwise sets it.
SET_ZERO(Operand);            // Sets the Zero Flag if the Operand is $#00, otherwise clears it.
ACCUMULATOR = Operand;        // Stores the Operand in the Accumulator Register.

Addressing Modes

Addressing Mode	Assembly Language Form	Opcode	# Bytes	# Cycles
Immediate	ORA #Operand	09	2	2
Zero Page	ORA Operand	05	2	3
Zero Page, X	ORA Operand, X	15	2	4
Absolute	ORA Operand	0D	3	4
Absolute, X	ORA Operand, X	1D	3	4*
Absolute, Y	ORA Operand, Y	19	3	4*
(Indirect, X)	ORA (Operand, X)	01	2	6
(Indirect), Y	ORA (Operand), Y	11	2	5*
* Add 1 if page boundary is crossed.