Date   : Tue, 17 Jul 2007 21:39:21 +0200
From   : kortink@... (John Kortink)
Subject: modern BBC remake

On Tue, 17 Jul 2007 17:02:05 +0100, "salahdin mahmud" wrote:

>I want to have a BBC computer made from the circuit diagrams available.
>The problem is that I'm not an electrical engineer and I don't know of this 
>is feasible?

Of course.

>If any engineers have any ideas?
>
>I know some other bbc addictss who would buy one if cost is reasonable.
>
>My personal reasons are:
>
>1) I've had a few BBC's which became faulty and cannot fix the problem and 
>its rare to get hold of a BBC in excellent all round condition.
>2) these BBC's already have  ware and tear so life is short.
>3) new parts available for repair
>
>Emulators are good but there are compatibility issues with some software and 
>a bbc replacement would work just like an original bbc.
>
>What do the rest of you think?

It's a recurring idea, and I've been toying with some
ideas myself. There's not that much to gain though.

There are many ways to mix the old and the new. You
could go whole hog and try and squeeze (almost)
everything into an FPGA, but that would take a lot
of development time, and would probably be relatively
expensive due to the cost of the relatively large
FPGA that would be required. On the other side of
the scale would be rebuilding the whole damn lot
with a new PBC but original parts, which is pretty
much madness.

I'd say the best would be somewhere in between. You'd
at least ditch some rarely used or practically obsolete
parts of the system like the tape and serial system,
speech, ADC, disc interface (replace by GoMMC ;-),
Econet, TV output. And at least put all ROM in a flash
ROM chip and all RAM in an SRAM chip, ditch some of the
logic as well (DRAM refresh, some glue logic). And put
almost all of the remaining glue logic in an FPGA. That'd
leave you with something like 9 chips (FPGA, SRAM, flash
ROM, two VIAs, CPU, CRTC, Teletext chip, video ULA) and
a little bit of peripheral logic and discrete components,
and relatively little FPGA development effort. Say a
third the PCB real estate. Relevant connectors in the
same place. Use the same boxes and power supply.

It'd not be cheap though. Somewhere between 50 and 100
UKP I'd estimate, and that's building cost only, with
most chips 'for free' i.e. salvaged from existing Beeb
hardware.

Given time, more chips could be put into the FPGA and
eliminated from the board. Less chips, smaller PCB,
more expensive FPGA.

Personally, I'd also consider bringing in Master (and
possibly B+) compatibility 'while you're at it' ...


John Kortink

-- 

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Homepage : http://www.inter.nl.net/users/J.Kortink

GoMMC, the ultimate BBC B/B+/Master storage system :
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