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