W H A T   C O M   P O R T S ?
          
          A COM port is a serial port which has a connector on the
          outside of the computer where you can plug in mice and
          modems and other serial devices. Internal modems have
          their own COM port. On an internal modem, the COM port is
          located on the modem card. A modem card plugs into an
          empty slot inside your PC. Such modem cards usually have
          two phone jacks--one for the phone line and the other to
          plug in a phone. Most modern computers have two COM
          ports--COM1 and COM2.
          
          
          DETERMING COM PORT USAGE WITH MSD
          
          You can often determine which COM ports (serial ports)
          your machine is using by running the DOS MSD (MicroSoft
          Diagnostic Utility) program. The MSD program comes with
          DOS 6.0 and later versions of DOS and with Microsoft
          Windows 3.1. So, if you have DOS 6.0 or later and/or
          Windows 3.1, you will have MSD. The SETUP installation
          program for any of the above mentioned programs will
          place the MSD program in your computer's path. To run the
          MSD program, at the DOS prompt type:
          
                                        msd <ENTER>
          
          When the MSD menu is shown on your screen, press the
          highlighted letter C for COM port information.
          
                                        c
          
          You will then see a screen showing what COM ports your
          machine is using. If you have a mouse installed, you can
          press the highlighted letter U for more information
          concerning your mouse. With the MSD menu showing on your
          screen, press:
          
                                        u
          
          MSD will then show you if your mouse is using a COM port.
          With MSD, you can press the highlighted letter Q to take
          a look at your IRQ (InterRrupt reQuest) addresses. With
          the MSD menu showing on your screen, press:
          
                                        q
          
          
          TIPS
          
          MSD sometimes does not correctly show COM port usage
          (especially COM4). However, a shareware program called
          Modem Doctor will correctly show COM port usage. If you
          are having modem problems, the shareware program Modem
          Doctor can really help. See the section on shareware for
          more information. Also, see the section on AT command set
          usage.
          

          DETERMINING COM PORT USE WITH MODE
          
          MODE.COM is a utility that comes with MS-DOS. If you have an
          older system and don't have the MSD program, you can
          often use the MODE command to see which COM ports are
          being used. To test for COM2, issue the following command
          at the DOS prompt:
          
                                mode com2 <ENTER>
          
          COM2 is being used if you get a report like:
          
          STATUS FOR DEVICE COM2:
          -----------------------
          RETRY=NONE
          
          If you get a report like the above, it means that the COM
          port for which you tested is being used. Just follow the
          MODE command with the COM port you want to test. 
          However, if you get a report like:
          
          ILLEGAL DEVICE NAME - COM2
          
          This means that the COM port for which you tested is not
          being used. If you have an internal modem, you may wish
          to set your modem to use that COM port. If you still have
          doubts about which COM ports are being used I would
          recommend that you obtain the Modem Doctor shareware
          program. Before you install an internal modem, be sure to
          read the next section on IRQs.


          DETERMINING COM PORT USAGE WITH DEBUG
          
          Another way to determine which COM ports are active on an
          MS-DOS computer is to use a utility that comes with DOS called
          DEBUG. This technique works with MOST machines. At the
          DOS prompt type:
          
                                        debug <ENTER>
          
          Then, when you have the hyphen prompt type:
          
                                        d40:00 <ENTER>
          
          The screen will show rows and columns with numbers. ON THE
          FIRST LINE, there are four sets of paired numbers that appear
          to the right of 0040:0000. These represent COM1, COM2, COM3,
          and COM4. You do not need to be concerned with the other seven
          rows of numbers. A zeroed pair of numbers indicates that the
          COM port is not being used. For example, suppose you see:
          
          -d40:00
          0040:0000  F8 03 F8 02 00 00 00 00-78 03 00 00 00 00 00 00
          
          Look to the right of the numbers 0040:0000. The F8 03
          indicates that COM1 is being used. The next set of F8 02 shows
          that COM2 is being used. The next pair of numbers (four zeros)
          tell us that COM3 is not being used. The following pair (of
          four zeros) indicate that COM4 is not being used and is
          available for a serial device such as a modem.
          
          Here is a key to the following possible hexadecimal numbers
          (note that COM3 and COM4 do not appear in the above example):
          
          F8 03 = COM1
          F8 02 = COM2
          E8 03 = COM3
          E8 02 = COM4
          
          To get out of DEBUG and go back to the DOS prompt type:
          
                                        q <ENTER>

          =============================================================