Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!europa.asd.contel.com!seka.scc.com!enger
From: enger@seka.scc.com (Robert M. Enger)
Newsgroups: comp.dcom.modems
Subject: Re: Why no PC modems without UART (re: Beware the Telebit T18pc)
Keywords: uart chip emulation modem
Message-ID: <1991Feb9.164603.17731@europa.asd.contel.com>
Date: 9 Feb 91 21:46:03 GMT
References: <1991Feb7.225401.28138@ingres.Ingres.COM> <1991Feb9.022024.10932@wsrcc.com> <23314@netcom.COM>
Reply-To: enger@seka.scc.com
Organization: CONTEL Federal Systems
Lines: 47
Nntp-Posting-Host: seka.scc.com

In article <23314@netcom.COM>, gandrews@netcom.COM (Greg Andrews) writes:
|> 
|> Indeed, why wouldn't other modem manufacturers do the same thing...?
|> 
|> Ever try to emulate a UART chip in software?  Ever wonder why the smart
|> multiport boards don't do it either?  It's a pain in the butt!
|> 

Dear Greg:

I believe one of (perhaps THE) main purposes of a UART is to perform
the serial<-->parallel conversion between the (serial) data communication
channel, and the host's (parallel, byte-wide) i/o data paths.  Is this correct?

It also my understanding that many of the fancier modems are already
operating on byte-wide data internally.  Some compression algorithms use
coding schemes based on reducing the bits required to transmit frequently
occuring symbols (characters or bytes).  The modem must also be able 
to recognize x-on and x-off symbols in the data stream, etc.  Thus it would
seem that most modern modems MUST view the host's IO stream in a byte-wide
(character oriented) fashion.

If these statements are true, then it WOULD seem desirable to eliminate
the UART from the data path between the modem card and the host.
Indeed, it would be nicer still to 'widen' the data path between the 
modem and the host.  That is, truly parallel-based internal modems
could utilize the full width of the I/O bus available in the host.
Still fancier optimizations are possible.  Modems could perform DMA
transfers to memory, become bus-masters, or employ other techniques to
lessen the per-character interrupt load on the host.

While these techniques seem feasible, they all require custom drivers
(and/or application programs) to operate the card.  This may render
some 'classic' pc-caliber software packages unusable.  So, the marketing
weenies will probably advise management against developing such products.

Comments?
Bob Enger
Contel Federal Systems
enger@seka.scc.com


-- 

Robert M. Enger
CONTEL Federal Systems
enger@seka.scc.com  (Internet)