With  DTE  is meant the Data  Terminal  Equipment  (Your
              terminal or Host computer) and with DCE the Data Circuit
              (termination)   Equipment  (all  equipment  between  two
              modems  RS232 plugs).  The HAYES-1200B is the 1200  type
              but as a card to be fitted into an IBM-PC.  The same for
              HAYES-2400B.

              The pin assignments must be in  accordance to ISO 2110.

              Pin #  Circuit  Towards  Description         1200 2400
                    EIA/CCITT
               1     AA 101   N/A      prot. ground          x    x
               7     AB 102   N/A      signal  ,,            x    x

               2     BA 103   DCE      transmit data         x    x
               3     BB 104   DTE      receive  data         x    x

               4     CA 105   DCE      request to send            x
               5     CB 106   DTE      clear to send         H    x
               6     CC 107   DTE      data set ready        R    x
               20       108.1 DCE      connect data set      x    x
               20    CD 108.2 DCE      data term. ready      x    x
               22    CE 125   DTE      ring indicator        x    x
               8     CF 109   DCE      data carrier detected x    x
               23    CI 112   DTE      select altern. rate        x
               12    CI       DTE      as previous (Bell212) x    x

               24    DA 113   DCE      TX-clock (DTE source)      x
               15    DB 114   DTE      TX-clock (synchr.)         x
               17    DD 115   DTE      RX-clock (synchr.)         x

              Remark: x means served by the modem.
                      H means tied to +10 volt (True).
                      R means tied to pin 8.
                      Pin  20  (DTR) can be simulated in the 1200  and
                      1200B type with a dipswitch.
                      Pin  6 and 8 can be forced to true in  the  1200
                      and 1200B type with a dipswitch.