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[edit | edit source]
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[edit | edit source]
ORA affects 2 of the CPU's status flags: