From: jim@n5ial.chi.il.us (Jim Graham)
Newsgroups: comp.dcom.modems
Subject: Help on upgrade to 16550A UART
Distribution: world
Date: Sat, 25 Jul 92 01:19:14 GMT
Organization: Me? Organized? Hah! :-)

I wrote:

>> of course, good
>> luck getting UART identifying software to know the difference....from
>> the programs I've seen, a visual of the chip is the only truly reliable
>> way to know what you've got.

geoff@zswamp.UUCP writes:

>    To the contrary, in my experience... there are chips labelled
> "8250" which are functionally identical to the 16450 (including such
> trivia as the scratch register).  I suspect - but have no proof - that
> NS doesn't make 'real' 8250s anymore, but ships 16450s labelled 8250
> because that's what people order.

8250?  or 8250A?  in the post where I listed the different types, I
did mention the 8250A, which was grouped right in with the 16450.  on
the other hand, you may well have a point --- NS might very well have
improved on the 8250 design in recent years, and either not announced
it as such, or perhaps, it didn't make the publication date for the
specs I've got (which was 1990, and shipped to me in the last 6 months
from NS themselves).

interesting question --- who's right?  beats me....  but then, I'm sold
on the 16550 these days, so to me, it's purely an academic question
(still, very interesting!).

and now to get on with the other followup.....

In article <uD4DoB4w164w@zswamp.UUCP> geoff@zswamp.UUCP writes:

> jim@n5ial.chi.il.us (Jim Graham) writes:
>
> > first, the old 8250 UART I once had installed most certainly refused to
> > be programmed higher than 9600 bps.
>
>    I don't get it.  You mean to say that it refused to register divider
> values that would result in speeds higher than 9600 bps?  How long ago
> was that?

the chip was in a serial board I bought around, oh, 1986 or so.  don't
know how old the board and chip were at the time....  and yes, it flatly
refused to be programmed higher than 9600 bps.

> > NS16550AF:                            DC to 256k      page 4-36
>
>    That last figure must be with a non-standard crystal, right?

well, let's see (now pulling out the NS data sheets again...hang on)....

yuck....3 different tables....if anyone's interested, I'll type up the
tables.  otherwise, I'll only hit a couple of entries from each (the
top 2 speeds).

All tables are from NS data sheets on NS16550AF, pages 4-50 to 4-51:

Table III. Baud Rates Using 1.8432 MHz Crystal
           |   Decimal Divisor
Desired    |   Used to Generate
Baud Rate  |   16 x Clock
-----------|----------------------
38400      |  3
56000      |  2


Table IV. Baud Rates Using 3.072 MHz Crystal
           |   Decimal Divisor
Desired    |   Used to Generate
Baud Rate  |   16 x Clock
-----------|----------------------
19200      |  10
38400      |  5


Table V. Baud Rates Using 8 MHz Crystal
           |   Decimal Divisor
Desired    |   Used to Generate
Baud Rate  |   16 x Clock
-----------|----------------------
128000     |  4          [42?  The Answer?  hmmm...the speed before
256000     |  2           128 was 56 kb, which is 6*9....perhaps NS
                          has some Hitchhiker's fans?  :-)     ]

is this helpful?
   --jim

--
Standard disclaimer....Ever since my cat learned to type, there's no telling
whose thoughts these really are....         73 DE N5IAL (/9)
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