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

    Purpose:        Decrement - subtract 1 from an integer
    Format:         opcode dif.mx
    Operation:      dif = dif - 1
    C. Codes:       N = dif LSS 0, Z = dif EQL 0
                    V = {integer overflow}, C = {borrow from MSB}
    Exceptions:     Integer overflow
    Opcodes:        97    DECB     Decrement byte
                    B7    DECW     Decrement word
                    D7    DECL     Decrement long
    Description:    One is subtracted from the dif operand and the
                    dif operand is replaced by the result.