🚀 go-pugleaf

mikel@networx.com (Mike Lempriere) writes:

>I'm building a TDD (Telecommunications Device for the Deaf) modem for
>my IBM PC.  I can't use the normal COM ports because TDD runs at 45.5
>baud, so I have to do it myself.

>From reading the PC newsgroups, a lot of people seem to be pulling out
>their old 16550 UART chips to put in the buffered 16550F version.

You want an 8250 or a 16450. The 16550 was a production glitch that the 
manufacturer did their level best to recall! That's why everybody
*really* wants 16550A chips (follow the A with various alphabet soup
to taste. :-)

BTW, if this is a *real* IBM PC, there are instructions available
for using the *cassette* port to drive an (included) circuit to do
TDD. 

And you can run the standard COM ports at 45.5 quite easily. You just 
have to load a "custom" value into the rate divisor register of the 
UART. A quick calculation shows that a value of 2532 will get 45.497...

And you are going to *have* to program right down to the hardware
anyway. The BIOS calls aren't going to help a lot.

-- 
Leonard Erickson		      leonard@qiclab.scn.rain.com
CIS: [70465,203]			 70465.203@compuserve.com
FIDO:   1:105/51	 Leonard.Erickson@f51.n105.z1.fidonet.org
(The CIS & Fido addresses are preferred)