The  Hayes modem has a minimum and a maximum baud  rate.
              If  you connect a terminal to the modem,  make sure  you
              have  the  right  pins connected in  relation  with  the
              dipswitches.  Also if you have selected e.g. 108/2 mode,
              be  sure  your  terminal  program support  them.  It  is
              possible to connect only the pins 2,3 and 7.  So in this
              case the DTR and the DCD are forced true.  In general  I
              don't  like this methode.  With the Hayes-1200,  RTS and
              CTS are not used,  so only full duplex is possible. With
              Hayes-2400 you have to use these signals only if you use
              the  Half  Duplex mode (Synchrone mode).  Otherwise  RTS
              (pin 4) is neglected and CTS (pin 5) is set true.
              So if you have connected the terminal properly,  at  the
              time you give an 'A' or 'a',  the modem decides what the
              baudrate   is  and  set  the  terminal  interface   UART
              according  to  it.  Hayes is very street  forward.  This
              speed  is maintained till after the  <carriage  return>,
              which  always finishes a command line.  With the next  A
              from a new AT command line,  a new speed can be defined.
              There is one other possibility.  In auto answer mode  or
              if a call is made, the baudrate can be else as the speed
              in  the  last passed command mode.  This on  real  modem
              level, the baudrate detection selects another speed. The
              Hayes reacts with the connect code on this last  command
              mode  speed and than switches to the new speed.  To give
              an example.  Suppose the terminalspeed is 2400  baud.  A
              dial  is made towards a 1200 baud only modem.  The Hayes
              will start the connect phase as described in 3.3.2.  but
              finally will get a connection on 1200 baud.  So he  will
              react   towards   the  terminal  with  2400  baud   with
              'CONNECT' or '1',  switches back to 1200 baud, which the
              terminal  has  to  follow,  otherwise  it  result  in  a
              terminal/modem mismatch. Also a <silence>+++<silence> on
              2400  baud will not be accepted.  Only 1200  baud,  from
              this moment on.  So suppose the established call at 1200
              baud  is  broken.  The  Hayes will,  after  the  carrier
              disappear,  fall  back into command mode still  in  1200
              baud.  The  terminal  has to give an AT<string> on  2400
              baud  if  it  wants the original  2400  baud  connection
              again.