Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!ucsd!ucbvax!hplabs!nsc!pyramid!prls!gordon
From: gordon@prls.UUCP (Gordon Vickers)
Newsgroups: comp.sys.ibm.pc.programmer
Subject: Re: How do get COMx to do 19,200 baud
Message-ID: <33150@prls.UUCP>
Date: 5 Mar 90 18:13:55 GMT
References: <32894@prls.UUCP> <2956@jato.Jpl.Nasa.Gov> <8422@chaph.usc.edu>
Reply-To: gordon@prls.UUCP (Gordon Vickers)
Distribution: usa
Organization: Philips Research Labs, Sunnyvale, California
Lines: 44

In article <8422@chaph.usc.edu> wilber@nunki.usc.edu (John Wilber) writes:
>I've got a few suggestions.  First, you can get some VERY HIGH baud
>rates from a serial port, as high as 100+ kbaud, if memory serves me
>correctly.  Programs such as LapLink, and the Norton Commander 3.0 do
>this with file transfers between PC's.

    Yes, I was aware of this and programming the UART isn't a concern.
  My concern is weather or not I can maintain realiable communications
 at 19,200 baud to this port when this port is stdin/stdout and to also 
 service COM2 at 2400 (or hopefully 4800) baud.

    Certainly, I can set up a UART for any valid baud rate that is within
  that part's range but this does not ensure realiabity.  The OS presents
  some amount of overhead from its system interupts and my application
  program will also add some amount of overhead as will our communications
  protocol. Additionally, we may add still more overhead for network (802.3)
  support.

    My concerns also involve thoughput (or effeciantcy). On some machines,
  a data transfer at 4800 baud (for instance) will complete is less time
  than the same trasfer done at 9600 baud.

    The serial cards I have seen do not buffer the incoming data and this
  bothers me, I've written ALOT of serial communications code (on a variety
  of other machines) and have never liked dealing with charector interupt
  devices.  What I would like to find is a serial card that
  does buffer the data and lets me know in some more polite manner
  that data is ready, and interupt me only if the high water mark is
  reached. If anyone knows of such a card then I would very much appreciate
  hearing about it since this type of solution would unburden the CPU
  enough to assure me that the PC will be a suitable platform.  Ideally,
  I'm looking for an RS422 serial card that supports tri-stating the
  transmitters but I could live with RS232 becouse I've already designed and 
  implimented an RS422 converter.

    I've never programmed an IBM PC, lots of other things, but not the PC.
    I'm not doing simple data transfers. I have to process packets, 
  issue ACK/NACKs and process the records enclosed in the packets which
  will likely result in an outgoing packet.
   
Gordon Vickers 408/991-5370, at Signetics  (Sunnyvale, California, USA )
{mips|pyramid|philabs}!prls!facv01!gordon       ** All disclaimers apply **
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