Date   : Sun, 10 Nov 1996 08:41:09 +0000
From   : Mike Tomlinson <mike@...>
Subject: Re: More Z80 co-processor questions

In message <Pine.SOL.3.95.961109184211.25311B-
100000@...>, Philip Blundell <pjb27@...> writes

>The Torch units
>_were_ disastrously incompatible -- I don't think they used standard Tube
>protocol at all.  You had to have an 'MCP' chip in the host to talk to the
>daughterboard, and the machine died if you didn't when DNFS tried to
>initialise the tube. 

They weren't that incompatible: I successfully copied several programs
from the Amstrad PCW, including some games, which ran fine on the Torch,
but locked up the Acorn Z80.

The PCW had no serial port as standard, so I put the 3 inch disk into a
Spectrum plus3 and squirted the files into the BBC over a serial cable.

The Torch MCP chip, as far as I can see, did the same job as Acorn's
Tube code, which was built into the DNFS. Instead of using Acorn's Tube
ULA, Torch used two back-to-back VIAs to handle the Tube, but the OS
calls in the BBC's OS ROM would have worked the same way in general, the
MCP rom handling the low-level stuff.

The Torch ROM also had some built in CP/M commands, so the Torch unit is
switch on and go, whereas a system has to be loaded from disc into the
Acorn unit before it will operate. Presumably the CP/M kernel is built
into the rom on the Torch card.

I also liked the way the Torch unit fitted inside the BBC. My Beeb had
in it at one point a fully populated ATPL rom board with sideways ram
upgrade, two battery backed sideways RAM cards, a Solidisk RTC, a
Watford 32k RAM card, the Torch card, and a 1770 DFS.

Needless to say, the PSU got rather warm, but the machine was reliable.
Actually, it still has all of the above in it apart from the Torch, and
boots quite happily today.

-- 
Mike Tomlinson
Cat Toy (n): anything not nailed down.