Path: utzoo!attcan!utgpu!watmath!att!dptg!rutgers!cs.utexas.edu!uunet!mcvax!ukc!axion!tigger!cag
From: cag@tigger.planet.bt.co.uk (Chris Green)
Newsgroups: comp.dcom.modems
Subject: Re: Minitel videotex terminals and v.23
Message-ID: <528@tigger.planet.bt.co.uk>
Date: 28 Jul 89 08:19:20 GMT
References: <817@sbsvax.UUCP>
Organization: RT5111, BTRL, Martlesham Heath, England
Lines: 35

> In article <431@siswat.UUCP>, buck@siswat.UUCP (A. Lester Buck) writes:
>> It seems that v.23 modems are quite expensive, around $800 and available
>> only in Europe.  Since the Minitel only costs something like $70-80, this is
>> something of a problem.  Assuming v.23 is basically 1200 baud in, 75 baud
>> out, what are the possibilities of using standard 1200 baud modem chips?
> 
There certainly are reasonably priced v21, v22, v22b and v23 modems
available, the one that immediately comes to mind is the (internal PC)
Amstrad MC2400 at about 170 pounds sterling and a similar external
model by Amstrad (SM2400 ?) at maybe 50 pounds more.

These Amstrad modems (and most other recent ones) have internal
buffering to allow the modem to PC link to run at 1200/1200 while the
modem to modem link runs at 1200/75.  It is possible to find v21/v23
only modems (rather old technology now) very cheaply indeed, mainly
because Prestel and others gave them away with Prestel subscriptions.
The main problem with these is that they are not buffered and thus
need a PC with a split speed serial port.  A standard IBM PC cannot do
this so comms programs which can use these older modems have to have a
software kludge to transmit at 75 while receiving at 1200.  It can be
done (I have a comms program called TranSend which does it very
successfully and emulates Viewdata on a Hercules display) but it is
not simple.

You could probably get a V21/23 modem for about thirty pounds sterling
and add about the same again for a program to handle the unbuffered
modem and you could probably do Viewdata on a PC for about $100.  Just
need a friend in the U.K. to go shopping for you.  If the requirement
is a one off (or so) I wouldn't mind helping.

By the way Prestel is now almost universally available at V22b so the
requirement for V23 modems is steadily tailing off now, I suspect that
it will soon be  a thing of the past.

Chris Green      cag@planet.bt.co.uk