BMI (short for "Branch if MInus") is the mnemonic for a machine language instruction which branches, or "jumps", to the address specified if, and only if the negative flag is set. If the negative flag is clear when the CPU encounters a BMI instruction, the CPU will continue at the instruction following the BMI rather than taking the jump.
BMI in comparisons
- Main article: Comparisons in machine language
LDA NumA Read the value "NumA" CMP NumB Compare against "NumB" BPL Larger Go to label "Larger" if "NumA" >= "NumB" ... Execution continues here if "NumA" < "NumB"
BMI only supports the Relative addressing mode, as shown in the table at right.
In the assembler formats listed, nn is a one-byte (8-bit) relative address. The relative address is treated as a signed byte; that is, it shifts program execution to a location within a number of bytes ranging from -128 to 127, relative to the address of the instruction following the branch instruction.
The execution time for BMI is not a fixed value, but depends on the circumstances. The listed time is valid only in cases where BMI does not take the branch. If it does take the branch, execution takes one additional clock cycle. Furthermore, if the branching crosses a page boundary, yet another cycle must be added to the execution time listed.
BMI does not affect any of the CPU's status flags.