DEC              Decrement                           Flags: O D I T S Z A P C
                                                            *       * * * *
DEC destination

          Logic:    destination . destination - 1

    This instruction decrements the destination by one. The destination
    operand, which may be either a word or a byte, is treated as an
    unsigned binary number.

  --------------------------------------------------------------------------
   Operands                  Clocks   Transfers  Bytes   Example
   reg16                       2          -        1     DEC BX
   reg8                        3          -        2     DEC BL
   memory                 15(23) + EA     2       2-4    DEC MATRIX[SI]
  --------------------------------------------------------------------------

       Note:          This instruction does not set the carry, so if you
                      need to decrement a multi-word number, it is better
                      to use the SUB and SBB instructions.