VMS Help MACRO, VAX MACRO Assembler, Instructions, BBxx  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Purpose:        Branch on bit - test and modify selected bit
    Format:         opcode pos.rl,base.ab,displ.bb
    Operation:      teststate = if {BBSS or BBSC} then 1 else 0;
                    newstate = if {BBSS or BBCS} then 1 else 0; temp =

                    FIELD (pos, 1, base); FIELD (pos, 1, base) =
                    newstate; if temp EQL teststate then PC = {PC +
                    SEXT (displ)}
    C. Codes:       Unaffected
    Exceptions:     Reserved operand
    Opcodes:        E2    BBSS     Branch on bit set and set
                    E3    BBCS     Branch on bit clear and set
                    E4    BBSC     Branch on bit set and clear
                    E5    BBCC     Branch on bit clear and clear
    Description:    The single bit field specified by pos and base is
                    tested. If it is in the test state indicated by the
                    instruction, the sign extended branch displacement
                    is added to PC and placed in PC. Regardless of
                    whether the branch is taken or not, the tested bit
                    is put in the new state as indicated by the
                    instruction.