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From: keating@motcid.UUCP (Edward Keating)
Newsgroups: comp.dcom.modems
Subject: Re: 4.77MHz PC sufficient for 19200 bps modem?
Message-ID: <7382@bone34.UUCP>
Date: 24 Jun 91 14:17:48 GMT
References: <243.2861EA82@zswamp.uucp>
Organization: Motorola Inc., Cellular Infrastructure Div., Arlington Heights, IL
Lines: 42

In article <243.2861EA82@zswamp.uucp>, root@zswamp.uucp (Geoffrey Welsh) writes:
> In a letter to All, Jonathan Hardwick (jch+@cs.cmu.edu ) wrote:
> 
>  >A housemate has an original Big Blue IBM PC, running at the 
>  >blazing
>  >speed of 4.77MHz.  We want to use this as a dumb terminal to 
>
> Question: Will a 4.77 MHz 8088 do 19,200 (9600) bps?
> 
> Answer: 9600 probably, 19200 probably not.  However, install an NS16550AFN 
> chip in place of the 8250 or 16450 chip on your serial port (and use software 
> which supports it), and the problem's solved.

  The answer to the question of whether or not a 4.77Mhz 8088 can do 19,200 is
  YES. Most laplink (or clones) programs run the comm port at 115Kbps which is
  in excess of 11k cps. My original PC-1 regularly performs this feat with
  an 8250 that has never been touched.

  The question that you should ask was, is there a modem program fast enough
  to display information at 9600bps. Most communication programs are limited
  by the display hardware involved and by the capability of the operator to 
  read the information that scrolls by. (You need a super fast reading course
  to keep up at the >9000 words/minute rate.)

  If all comes down to time. At 1920 cps you receive characters every 
  520 microseconds. If the communication program attempts to display every
  character as it is received, then you will fall behind. To keep up with the
  comm link, the communication program will have to buffer characters from the
  link and display them as a string. This leads to a display that is hard
  to read. (It becomes a very "jerky" display). Displaying characters as they
  are received has a smoothing effect so that it becomes more readable.
 
  Dec Vt100s with "smooth scrolling" enabled do not display more than 120cps
  effective rate. They control the host with an excessive amount of XON/XOFF
  characters.

  If you are evaluating communication programs, Procomm 2.4 will keep up with
  the comm link at 240 - 480 cps. Procomm Plus will display 2-3 times faster
  (again, your mileage may vary depending on your display adapter. CGA is
  worst, MDA with the long persistence monitor is better, and EGA/VGA are
  usually faster. Check out the PC Mag reviews for the fastest display times
  of cards for the mode you wish to operate in, text/graphics and pick a card.)