ComInst()

         Installs a Serial Comunications System

    Syntax:

         ComInst( nPort ) -> nError

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

    Description:

         ComInst() installs a Serial Comunications System and initializes
         comunication buffers.

         DANGER
         The interrupts manager must be uninstalled by the ComUnInst()
         function before to leave the operating system. In other case
         it will have a general break down of the system.

    Return:

         A number with the next meaning

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

    Example:

         ComInst( 2 )           // installs the manager on COM2