From: galway@chtm.eece.unm.edu (Denis McKeon)
Subject: Re: 16550 Uart questions..
Date: Fri, 25 Dec 92 16:41:16 GMT
Organization: Connemara - Computing for People
Distribution: usa
X-Mailer: Mail User's Shell (7.0.1 12/13/89)
Bcc: Gaia@carson.u.washington.edu
Status: OR

In article <1992Dec25.125953.27654@u.washington.edu> gaia@carson.u.washington.edu (I/We are Gaia) writes:
>I just started reading this news group, and have read all I can on this
>particular subject here, but didn't seem to get an answer to my particular
>questions, so I guess I have to ask anyway..
>
>I just got a SupraFAXmodem v.32bis, my are the threads here vicious on
>them, but so far I haven't had any problems at all, I do seem to have the
>1.200-H revision roms.  Are these the most recent?? Anyway, I had to put
>the com software down to 19,200 since the 8250/16450 uart just spits at
>38,4 or 57,6.  Here is my question..

One guy here is vicious about Supras, but the consensus seems to be that
there are some bad modems in the barrel, and he got 4 in a row.  Yuck.

The 1.200-H roms are the most current type for externals modems - the
internals have the 1.200-L, and the Caller-ID Roms are a 1.2-J.

When you say "uart just spits at 38,4 or 57,6" do you mean in response to 
the Dos mode command, or in response to setting Procomm at 38,4 or 57,6?  
For me, "mode com2: baud=19200" produced an error even on a 16550, but
Kermit, Procomm 1.1B and DSZ all run happily at 57600 DTE.  Wierd.

>I have a generic 8 bit multi-io card, and the manual that came with it,
>actually better than most I have seen, it actually gives details.  It
>says to enable the second serial port I have to insert the following Ic's:
>1488,1489,and 16450 (I assume this is the uart), I have seen the card, it
>does have both serial ports installed, and the base seems to be setup the
>same way.  In order to get the advantage of the 16550, can I just unplug
>the 8250/16450 and plug in a 16550??  Do the other 2 chips (small like
>drams) need to be replaced, if so with what??  Does it need to be a 16bit
>card??  And finally where can I get a genuine National Semiconductor
>16550AFN if all this is possible, for a decent price.  

I am in a similar setup - Supra V.32bis, 1.200-C Roms w/ no problems so
far, and I swapped a (socketed) 16550 into a generic 8-bit card also. 
The smaller chips were soldered in place under the previous 16450, so I
left them there, and I haven't had any problems so far - but I've only
had the modem for 2 days, and I haven't stress tested the Uart with
highly compressible throughput.  I figure that the 16550 and the smaller
chips will either work together or at least peacefully coexist, and
should certainly not break each other - I hope.

Where to get a 16550?  People on the net quite cheerfully pointed to 
several large mail-order electronic parts places - usually Fry's,
Arrow Electronics and either JDR or JD&R.  When I called, however,
Arrow said they didn't handle National Semiconductor chips; Fry's
took my toll call on voice mail, then gave an internal busy signal,
so I never called back; and I never found a number for JDR or whatever.

The yellow pages led to a total of 10 other local parts and computer
places, each referring me to another 1 or 2, and finally to a place that
pulled a 16550 and the other two chips from a card, and sold them to me
(for $25 - a bit steep).  One of the other places had a price of $9.15, 
(perhaps for only the uart) but wanted 8 weeks for delivery - NOT!

The moral is: call around.  If you are asked for a part number, respond
with "NS16550AFN" - you don't need an AFN, as apparently an AN will do
for the PC environment, but do not use "16550" only.  There is a mild
argument in progress in comp.dcom.modems as to whether clone 16550 chips
made by Goldstar or others are just as good as NS, or equal to trash.
Mine is a Goldstar, as was the 16450, and I haven't seen any problems -
yet.  Get a NS if you can, but settle for a clone if you want to.

As a software type feeling somewhat lost in the hardware world, I found
that using the following mantra with each call got good results:

    "Hello, I'm looking to buy a single chip - a UART for a PC - 
     do you handle those?"

    "What's the part number?"

    "NS16550AFN"

The buzz about the "single chip" and "PC" established that I wasn't
looking for a price per thousand, and that I probably didn't know much -
that way I didn't have to deal with an outrush of hardware jargon :-)

Good luck.

--
Denis McKeon
galway@chtm.eece.unm.edu

QED: Quit and Eat Dinner