Date   : Sun, 19 Mar 2006 11:51:52 +0000
From   : Rob <robert@...>
Subject: Re: Modems (was: 6502s and SASI/SCSI.)

At 10:24 19/03/2006, gARetH baBB wrote:


>I suspect the Nightingale AA board just detects line reversal.

There was quite a bit to it .. I think it handled the auto-answer 
too.  I've got the protptype board, somewhere, but no modem..

Back then, there were two distinct schemes for auto-answer, I seem to 
recall.  There was "modem answers call autonomously, negotiates 
carrier.  Carrier-detect is fed to CTS on beeb, which registers call 
and starts sending."   This needed a little more circuitry in the 
modem, and is normal mode for "hayes" type intelligent modems. "ATS0=1")

Then there was the "simple ring-detect fed to CTS on beeb, which 
spots it, raises RTS to make modem goes off-hook and negotiates 
connection. Beeb waits for something from user (normally CR) or 
simply times out."  This was the more basic modems, including the old 
GPO modem rack that I wrote OBBS originally for!

In both cases, you usually dropped RTS to drop the line: modem goes 
on-hook and connection is broken.


>I wasn't going to go as far as doing "dialling" though, just straight
>connection between the two and a relay to cut the "line" for when a user
>logs off so the carrier drops.

You should just be able to drop RTS, depending om modem and how the 
cable is wired up.   The nightingale always was the "odd one out" as 
far as controlling it went, though...  I ditched it ASAP...

Rob