Date   : Thu, 14 Feb 1991 02:10:28 GMT
From   : agate!bionet!uwm.edu!cs.utexas.edu!news-server.csri.toronto.edu!utgpu!attcan!john@ucbvax.Berkeley.EDU (John Benfield)
Subject: Is my machine too SLOW for 2400bps modems?

In article <7015.27b26608@cc.curtin.edu.au>, Murray_RJ@cc.curtin.edu.au writes:
> In article <316@fxrs.intel.com>, jmasters@fxrs.intel.com (Justin Masters)
writes:
> > 
> > I have a Radio Shack model 4 w/ Montezuma Micro's CP/M 2.2.  I bought
a 2400
> > buad modem a few months back, and while I've endured a problem with not
> > getting the first characters of the line, I can't stand this problem
anymore.
> > 
> > I'm using Qterm 4.2f and I've also used MEX 1.12 (or some old version like
> > that).  Both worked beautifully for me when I had 1200 baud capability, but
> > now it seems that 2400 baud is too fast.  Is this true?  How do I fix
it?  Is
> > it a problem of my machine waiting too long at the end of the line before
> > continuing on to the next line?
(text ommitted)
> processor must scroll the screen up one line whenever it sees a line feed. If
> your system has a separate video controller then it doesn't usually take too
> long and characters are rarely lost even at high baud rates. If your main
> processor has to do all the work then characters will probably be lost. The
> original Apple IIs with 80 column cards were bad in this respect: they'd
> even lose about 5 characters at 300 baud.

The ModelIV does not have a dedicated video display system. This leaves
3 options. A modem with a good character buffer that captures in response
to a flow control signal from the PC. (ie. drop DTR before each scroll
call). 2) Line delays on the BBS. (beware of using nulls for timing loops
with the ModIV. Some comm packages actually display the NULLs). 3) Cyclic
(non)Scrolling. Write your term emulator to go to the top line of the screen
instead of scrolling when it hits bottom. DO NOT TRY TO DO A SCREEN CLEAR
WHEN YOU HOME THE CURSOR! Clear screens on the IV take 400-700ms. Enough time
to lose MAJOR amounts of data. When I implemented kermit on the IV, I had
to disabled the status display because it actually slowed down the system 
enough (doing cursor addressing) to drop characters often enough to piss me
off. 

Cheers.

______Opinions stated are my own. Transcripts available by request______
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