The first thing you should do is to make sure COM1 is even set up correctly on
your computer. On older computers the COM ports were automatically enabled,
but on newer computers they aren't always turned on. I think the easiest way
to check is to get into DEBUG (from the DOS prompt and enter: D 40:0 The base
I/O addresses of the first four COM ports are listed at this address, with COM1
usually being at address 03F8h. Intel stores number in little-endian format,
so the first two byte you should see are F8 03. You can quit DEBUG with a: Q If
the first two bytes you see are not 03F8, you have a problem. If they are
0000h, COM1 is not set up in the BIOS. You'll need to get into the BIOS setup
(usually by pressing some special keystroke combination as the computer is
first booting up) and enable COM1. Keep in mind that it's also possible to have
two different sets of COM1 hardware (for example, one on the motherboard and
one on a plug-in card). If you have something like that going on, things get
REALLY screwed up and you never how how the computer will react. If that is
working OK, you can try my SERIAL program (available at http://bretjohnson.us)/
It's a TSR that shows the status of a serial port on the screen in "real
time". Actually, what SERIAL does is constantly poll the UART (Universal
Asynchronous Receiver/Transmitter), which is the chip that the computer uses to
control the serial port. It will show you the status of all the serial port
pins (including RTS & DTR) as the UART sees them. If you're not using hardware
flow control (and both the computer and the device at the other end of the
serial cable both know that) then the status of the pins doesn't matter. But,
it's still good to know that they work in the UART to make sure everything is
OK.
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