COMPORTS.EXE - copyright 1989 Phil James

This program actually does a check of your hardware to determine the
existence of any serial ports, much as ROM BIOS does at bootup (Power On
Self Test). On many non-PS/2 machines, however, only COM1 and COM2 are
checked. This program checks COM1 through COM8 and updates the BIOS data
area to reflect the existence and the addresses of *all* serial ports.
This prevents problems when trying to access COM ports beyond COM2 through
DOS, for instance when using the MODE command or redirection. This program
will work for all PCs, XTs, ATs, PS/2s and compatibles. Please remember
that DOS 3.3 or later is required for any DOS services to work on greater
than COM2, and even these late versions of DOS don't support beyond COM4.

The addresses checked for the existence of physical ports are as follows:
COM1 - 3f8 (hex)
COM2 - 2f8
COM3 - 3e8 and 3220
COM4 - 2e8 and 3228
COM5 - 2e0 and 4220
COM6 - 3e0 and 4228
COM7 - 5220
COM8 - 5228