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CWD              Convert Word to Doubleword          Flags: not altered

CWD

          Logic:    if (AX < 8000h) then
                        DX . 0
                    else
                        DX . FFFFh

    CWD extends the sign bit of the AX register into the DX register. This
    instruction generates the double-word equivalent of the signed number
    in the AX register.

  --------------------------------------------------------------------------
   Operands                  Clocks   Transfers  Bytes   Example
   no operands                 5          -        1     CWD
  --------------------------------------------------------------------------

       Note:          This instruction will set DX to 0FFFFh if the sign
                      bit (bit 15) of AX is set; if bit 15 of AX is not
                      set, DX will be set to 0.