ORA

ORA (short for "Logical OR on Accumulator") is the mnemonic for a machine language instruction which performs a bit-wise boolean "or" between each of the eight bits in the accumulator and their corresponding bits in the memory address specified. The eight resulting bits form a byte, which is stored in the accumulator.

Addressing modes

Opcode		Addressing mode	Assembler format	Length in bytes	Number of cycles
Dec	Hex
9	09	Immediate	ORA #nn	2	2
13	0D	Absolute	ORA nnnn	3	4
29	1D	Absolute,X	ORA nnnn,X	3	4*
25	19	Absolute,Y	ORA nnnn,Y	3	4*
5	05	Zeropage	ORA nn	2	3
21	15	Zeropage,X	ORA nn,X	2	4
1	01	Indexed-indirect	ORA (nn,X)	2	6
17	11	Indirect-indexed	ORA (nn),Y	2	5

ORA supports eight different addressing modes, as shown in the table at right. In the assembler formats listed, nn represents a single-byte (8-bit) figure, and nnnn is a two-byte (16-bit) address.
With some addressing forms (marked with an asterisk, *, in the "Number of cycles" column) the execution time for ORA depends on the circumstances: In cases where the indexing requires the CPU to "reach across" a page boundary from the base address, the execution time is 1 cycle longer than listed here.

CPU flags

ORA affects 2 of the CPU's status flags:

• The negative status flag is set if the result is negative, i.e. has its most significant bit set.
• The zero flag is set if the result is zero, or cleared if it is non-zero.