ComInst()

         Installs a Serial Communications System

    Syntax:

         ComInst( nPort ) -> nError

         nPort : COM port. 1=COM1, 2=COM2, 3=COM3 and 4=COM4

    Description:

         ComInst() installs a Serial Communications System and initializes
         the communication buffers.

         DANGER
         The interrupt manager must be uninstalled by the ComUnInst()
         function before you leave the system.  Otherwise, it will cause a
         general break down in the system.

    Return:

         A number with the following meanings:

           0    Ok
           1    A port out of the range 1-4 was specified
           2    There's no UART for the specified port
           3    The manager was already installed

    Example:

         ComInst( 2 )           // installs the manager on COM2