WANTED: Your old 16550 UART

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2 total messages Started by Mike Lempriere Mon, 21 Dec 1992 18:30

#722

Author: Mike Lempriere
Date: Mon, 21 Dec 1992 18:30

16 lines
1171 bytes

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.

I'm running so slow you can outtype it without even trying!  I can use
the old slow UARTs just fine.

I will meet you at the espresso stand of your choice (I work in Bellevue,
but I always want an excuse to do the U-district) at your convenience.
I don't know how much they cost new, but it's certainly worth the cost
of Grande Mocha to me.

Please respond via e-mail, to reduce bandwith -- Thanks in advance!

Re: WANTED: Your old 16550 UART

#761

Author: Leonard Erickson
Date: Fri, 25 Dec 1992 12:12

30 lines
1763 bytes

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)

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