Date : Mon, 25 Jan 2021 12:37:06 +0000
From : pete@... (Pete Turnbull)
Subject: Completely expanded "Cheese wedge" BBC Micro - just
On 25/01/2021 11:12, lug@... wrote:
> * Teletext adapter (useless now I know)
> * Prestel adapter (again probably useless)
> * 2^nd processor
> * IEEE interface
> * Z80 2^nd processor
>
> I think there were one or two others (Econet bridge?).
The Econet Bridge was a separate box, as was the X25 Interface. There
was a genlock unit that was used for TV programs such as "Making The
Most of the Micro" and "Micro Live" but it wasn't ever sold as a
production device. Offhand, I don't remember any others that used the
cheese-wedge box, though there were several 3rd party add-ons that used
the 1MHz bus.
As for 2nd processors, there was the original 6502 2nd Processor, which
is presumably what you meant above, and the ARM Evaluation Kit, two
versions of the Cambridge Co-Processor (one of which was also known as
the 32016 Coprocessor), and a 6809 coprocessor (never sold to the public).
It was possible to run the Teletext Adapter and the Prestel Adapter side
by side, because the Prestel Adapter used only the RS423 connection. It
was driven with a bizarre protocol which drove the developers nuts
because a certain Acorn director insisted it not use the User Port or
1MHz bus. I did some minor debugging of the firmware (which was written
by SoftMachinery). And of course you could connect one, or in the case
of the Master 128, two coprocessors as well. The Master could take one
internal and one external copro, but it could only use one at a time.
It was also possible to run two 2nd processors on a Model B. The 6502
and Z80 2nd processors had jumper links for one of the enable lines and
the power. I had a pair piggybacked together, powered over the Tube,
with a two-pole two-way switch to swap between them.
When the Master 128 came along, there was a Universal Coprocessor Box
which could be used with a Model B or Master, and which could take the
later 65C102 intended for the Master Turbo, the 80186 copro for the
Master 512, or the 32016 for the Master Scientific. A third party
developed an 80286 copro and some work was done on an 80386 as well, but
neither made it to production. Too many difficulties and too much work
for too little return, by that time.
The last "copro" was the A500, which was the development unit for the
Archimedes. Rather than being intended to give a Beeb superpowers, it
was intended to give an ARM processor access to I/O. It was a plain
blue-grey metal box similar in size to an Archimedes, with a Tube Podule
(one of which I still have) to connect to a Model B. Various
incarnations offloaded less and less to the Beeb, and several of those
units were eventually provided to the ISPs who were developing software
prior to the Archimedes launch in July 1987.
--
Pete
Pete Turnbull