UPGRADING REPAIRING PCs

Avoiding Conflicts with Serial Ports
Use Table 6.7 to understand possible conflicts with serial ports and
avoid them.
Table 6.7 Troubleshooting Serial Port Conflicts
Problem Reason Solution
DOS-based DOS and PC BIOS Disable COM 2 and set new device to
program can’t support COM 1 use COM 2; use Windows program instead
find COM 3 or
4 on modem or
other device
and 2 only
Device using Shared IRQs don’t Relocate IRQ for device to a different port.
COM 3 or 4 work for ISA If device is external, connect to multiport
conflicts with devices board. (Windows 95/98/NT/2000 can
COM 1 and 2 handle up to 128 serial ports!) (see earlier)
Note
For modem troubleshooting, see the section “Modems” later in
this chapter.
Troubleshooting I/O Ports in Windows 9x and Me
Windows 9x and Me can tell you whether your ports are functioning.
First, you need to verify that the required communications
files are present to support the serial ports in your system:
1. Verify the file sizes and dates of both COMM.DRV (16-bit
serial driver) and SERIAL.VXD (32-bit serial driver) in the
SYSTEM directory, compared to the original versions of these
files from the Windows CD-ROM. They should be the same
date or later, not older.
2. Confirm that the following lines are present in SYSTEM.INI:
[boot]
comm.drv=comm.drv
[386enh]
device=*vcd
Serial Port Configuration 173
The SERIAL.VXD driver is not loaded in SYSTEM.INI; instead, it is
loaded through the Registry.
If both drivers are present and accounted for, you can determine
whether a particular serial port’s I/O address and IRQ settings are
properly defined by following these steps (which also work with
Windows 2000):