skl@van-bc.UUCP (11/11/87)
For those of you who had been pulling your hair out wondering why
UUPC works on one IBM-PC clone but refuse to talk to the serial
ports on another, this might be good news for you...
On some combinations of IBM-PC clones, third-party BIOS, and internal
Hayes-compatible modems, the low-memory serial port addresses table
maintained by the BIOS at 47:0 does not get initialized by the BIOS
correctly during the power-up self-test initialization, and therefore
pointing to incorrect addresses for the serial ports. In this case,
UUPC will happily use the values provided by the BIOS table as the
serial ports' base addresses, and consequently gets no where when
trying to talk to the serial ports.
To check if your PC/XT/AT clones have this problem, go into DEBUG and
use the command 'D 40:0 7' to examine the values of the BIOS' serial
port addresses table. If the output looks like
0040:0000 F8 03 00 00 (for a 1-serial-port system)
0040:0000 F8 03 F8 02 (for a 2-serial-port system)
then your table is fine. Otherwise, this could be the problem that
has been preventing you from using UUPC on your system.
The fix to this problem is fairly straight forward, all you need to
do is write a small program (in whatever language you like) to poke
the appropriate port addresses back into the port table, and invoke
this program in your AUTOEXEC.BAT file. As a fast and very short-term
fix, you could also hand-patch the correct port addresses in using
DEBUG, but this fix will only last until you turn off your machine.
Good luck, and send me e-mail if you have further questions on this.
...Sam
--
Samuel Lam <Samuel.Lam@van-bc.UUCP> or
{ihnp4!alberta,watmath,uw-beaver}!ubc-vision!van-bc!skl