To all those wanting to run more than two PC COM ports.

From my experience, it is not worth trying to get a second serial port board
in a PC.  It may be possible to get shared use of IRQs IF both boards are
from the same manufacturer AND they are designed for shared use.  Otherwise,
you will have to buy a specialised multiple port board.  I have a catalogue
from CAPAX Industrial PC Systems Ltd which includes a wide range of boards
with four and eight RS232 and/or 422 and/or 485 ports.  They can be emailed
on ipc@capax.co.uk or (in Sweden) ipc@capax.se and are on the web at
http://www.capax.co.uk/.  These and/or similar boards are probably available
from other companies (eg stocked by Maplins in the UK,
http://www.maplin.co.uk) - my point is that they exist.  Since these boards
are not everyday items, they aren't cheap in comparison with standard "Multi
I/O" boards - cheapest Capax 4 port is 53 UKpounds before tax.

As a cheaper alternative (which I've used for ages), buy a port switcher.
For most applications you only need a five-line type, not the full 25-line
"T-switch" that used to be common.  I also use a 4 way "Palm Printer Switch"
port switcher on LPT1 to cope with fussy dongles and parallel port
programmers - this was bought from Maplins for 25 UKpounds and has given
excellent service.

Tim Forcer                 tmf@ecs.soton.ac.uk
Department of Electronics and Computer Science
The University of Southampton, UK

PS - Thanks to Microchip for fixing the email bounce.