Optimizing the Windows Serial Interface for High Speed Connections


For optimal data throughput, we recommend setting you communications
software's serial port(baud) rate at the highest possible speed(i.e.
19,200, 38400, 57600, or 115200 bps). Take note, not all computers
have a serial interface that can support the higher connection speeds.
How fast your computer's serial interface can go, depends on what type
of UART chip and communications driver your computer uses. To optimize
your computer's serial interface, you will need to know the following:

  *  The COM Port your modem is attached to.
  *  What type of UART(see document 10589) chip is in your computer.
  *  The Port Address of the COM Port the modem is attached to.
  *  The IRQ of the COM Port the modem is attached to.


Using MSD
To locate the above information, you can use Microsoft's diagnostics
program included with most versions of MS-DOS. If you do not have
access to DOS, consult your operating system manual for information on
how to access this data. Use the following steps to access this
information in DOS:

  1.  Exit Windows completely. Do not open a DOS Window.
  2.  Turn on your modem.
  3.  At the DOS prompt, type MSD and hit ENTER.
  4.  Select C to view the serial device settings.
  5.  Find the line UART Chip Used, and cross over to the COM Port 
      your modem is on(the COM Port that has both DSR and CTS marked 
      with a "Yes" is your modem). Write down the UART type and the 
      Port Address(e.g., 02F8H) on the worksheet below.
  6.  Press ENTER to exit the COM Ports Window, then press Q to 
      enter IRQ Status.
  7.  Locate the line that contains your modem's COM Port(e.g., 
      COM2) and write down the IRQ number at the beginning of that 
      line(i.e., "3").
  8.  Exit MSD and run Windows again.
     
     Worksheet
        COM: ___ UART Type: ________ Port Address:__________ IRQ: ___

After you have successfully determined what type of UART chip your COM
Port is using, run your communications program and set the serial
port(baud) rate according to the following guidelines:

UART 16550 or 16550AF  Set your communications software to the highest
                       serial port rate it allows(up to 115200). If
                       you encounter problems after changing the
                       port rate, try lowering it one setting.

UART 16450 or 8250  Set your communications software's port rate to
                    19200.


Modifying your SYSTEM.INI File
Windows 3.1/3.11(not Workgroup), uses a communications driver called
COMM.DRV.  Your modem's performance can be improved by replacing this
default communications driver with a different driver, such as
WFXCOMM.DRV(download off our BBS at 847-982-5092 or FTP Site at
ftp.usr.com) or CYBERCOM.DRV(see document 10251). These files are
placed in your WINDOWS/SYSTEM directory.

Note:  Your communications software may have already replaced this
       driver. The examples below show you how to check if you are 
       still using COMM.DRV.


Changing the Communications Driver
The following steps describe the process of replacing the COMM.DRV
setting in your Windows SYSTEM.INI file, with the new driver:

  1.  Make a backup copy of your Windows SYSTEM.INI file.
  2.  Open Windows Notepad in the Accessories group.
  3.  Under File/Open type SYSTEM.INI as the filename, and press 
      ENTER.
  4.  The SYSTEM.INI file is broken into sections, each separated by
      bracketed text. The first section, the [boot] section(pictured 
      below), is where COMM.DRV is assigned.
     
     Figure 1. The [boot] section of the SYSTEM.INI file:
          [boot]
          shell=progman.exe
          mouse.drv=mouse.drv
          network.drv=netware.drv
          language.dll=
          sound.drv=mmsound.drv
          comm.drv=comm.drv
          keyboard.drv=keyboard.drv
          system.drv=atmsys.drv
     
     Note:  If your communications software has already replaced the
            COMM.DRV driver with its own driver, you can use that 
            driver and skip to step 5.
       
          Change the line:
       
            comm.drv=comm.drv
              to
            comm.drv=wfxcomm.drv
              or
            If you install Cybercom, the installer will take care 
            of this for you.

     Note:  If you are running Windows for Workgroups, Windows 3.11,
            Windows 95, or Windows NT, do not replace the default COM 
            driver.
     
  5.  Make changes to the serial interface parameters, as outlined on
      the next page.


Changing the Serial Port Interface Parameters
Page down to the end of the [386enh] section of the SYSTEM.INI
file(right before the next set of brackets). There should be a list of
parameters that starts with COM. Below is a list of settings or
parameters for the Windows serial port interface:

     1.  Check to see if you have the following lines:
     
          COM3Base=3E8h
          COM3Irq=4
          COM4Base=02E8
          COM4Irq=3
     
        If you do, delete them, or remark them out as shown below:
          
          ;COM3Base=3E8h
          ;COM3Irq=4
          ;COM4Base=02E8
          ;COM4Irq=3
     
        Note:  Only delete or REM out the lines shown above. Do not
               REM out any other lines that begin with COM.

     2.  Consult the worksheet on Page 1 to make the following 
         additions and/or changes:

         Where:
                 X = the COM Port your modem is attached
                 BBBB = the COM Port's port address
                 Q = the COM Port's IRQ
     
         For Windows 3.0 and 3.1, or Windows for Workgroups with any
          UART type:
       
          comboosttime=30
          comXbase=BBBB
          comXirq=Q
          comXautoassign=1
          comXbuffer=512
          comXfifo=0
     
         If you have a 16550 or 16550AF UART chip, make the above
          changes, but set the FIFO equal to and add the additional
          settings below:
       
      For Windows 3.0 and 3.1:    For Windows for Workgroups 3.11:
           comXfifo=2                      comXfifo=2
           comXtxsize=12                   comXtxfifo=1
           comXrxsize=8                    comXrxtrigger=8