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000297_news@newsmaster….columbia.edu _Wed Nov 19 10:39:15 1997.msg
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From: fdc@watsun.cc.columbia.edu (Frank da Cruz)
Newsgroups: comp.protocols.kermit.misc
Subject: Re: How fast will a 16550 go?
Date: 19 Nov 1997 15:39:13 GMT
Organization: Columbia University
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In article <HMvc0w8Z7WcC092yn@netcom.com>,
Jeffrey Hurwit <jhurwit@netcom.com> wrote:
: I would like to use MS-Kermit on two mahines connected by a null modem
: cable to transfer files. What is the maximum safe speed of a 16650 FIFO
: UART?
:
Good question. I don't know the answer; maybe somebody else has the
National Semiconductor specs. Also note that not all 16550s are the same;
there are differences, hopefully noted in the letters that follow (A, AFN,
etc; reportedly AFN stands for All Fixed Now).
The real limitation more likely lies in what's beyond the UART. How fast
can the PC service interrupts? And on the other side, how good is the
cable? For speeds of 115200 and higher, a regular cable often is not good
enough; instead you might need a short, shielded and/or low-capacitance
cable. And of course, all the usual cautions about interrupt conflicts, CPU
contention, etc, apply.
On some PC-based operating systems (e.g. SCO OpenServer 5.0.4), it is
possible to select serial speeds as high as 921600 bps. But who knows if
they work. In any case, the highest speed supported by MS-DOS Kermit is
115200 bps.
The best answer to a question like this is "try it and see". For best
results, leave Windows out of the picture.
- Frank