ON BAUD RATES, UARTS, MODIFICATIONS AND SO FORTH


Generally, using the highest baud rate possible gives the best
overall performance, since once the CPU goes to read a byte from
the com port, it wastes a lot of machine cycles waiting 
for each little bit to come in across the serial port.  The
slower the baud rate, the longer it waits.   While it is 
"waiting" it will be unresponsive to user actions such as mouse 
and key clicks.

However, Windows in standard mode usually cannot handle baud rates
of 9600 or higher.  This is due to the fact, that in standard mode
Windows has to switch CPU states and reset the CPU every time it
reads from the UART (Universal Asynchronous Receiver/Transmitter),
an integrated circuit that handles serial I/O for the CPU.  The
16540 or older 8250 UART can only buffer one byte at a time. 
If another comes in before the CPU reads it, a condition called 
"hardware overrun" occurs.  

If you need to use a 286 in Standard Mode, altering the [standard]
section of SYSTEM.INI with "FasterModeSwitch=1" may help.
This has no effect on 386 models, and may cause some older models
of the IBM AT or compatibles to hang due to an imcompatible BIOS.

In 386 enhanced mode, 19200 baud should be OK, especially if
you have a newer type of UART, the 16550, which has a 16 byte
buffer.  

If you're using the PCB-88, you can replace the existing 16540
chip (look for a large-ish dual inline package with PC16450CN on it)
with the newer 16550AF or AFN.  They are completely pin-compatible.
This should eliminate any overrun problems. As usual when working 
with computers, beware of static discharges.

If you're using the PK-88, or a Tnc that connects to your
RS-232 port, the UART chip will be on the serial card in your
computer.  If you are unsure which type of UART you have, you
can run MSD.EXE (found in the Windows directory) to find out
which it is.  This must be run from DOS, and you need to reboot
the computer after running it because it has a bug and messes
up the port BIOS information.  

There is one potential problem with 19200 baud, however.
I don't know if it is a problem with the pcb-88, or a slight
incompatibility in my system, but my computer tends to 
spontaneously reboot every once in awhile when using the 19200
baud rate.  Switching to 9600 baud cures the problem for me.