Date   : Sun, 22 Sep 2002 00:54:06 GMT
From   : pete@... (Pete Turnbull)
Subject: Re: BBC B with edge-connectors instead of IDC connectors?

On Sep 21, 16:31, Richard Gellman wrote:
> To summarise everything:
>
> I concur on the Model A thing. As soon as you said "No analogue port" I
> thought "upgraded Model A".
>
> There is a book called "Programming the BBC Micro" which has near the
back a
> list of components that have to be fitted to upgrade an A to a B.
> They're all "off-the-shelf" components, so back then the average
electronics
> hobbyist could do it easily and cheaply (in fact, for probably less than
the
> price difference between an A and a B at the time). Another thing to keep
in
> mind, is that the Model B is overly versatile, that is to say, a lot of
> people will never use *every* interface on their computer, and as such,
if
> one is upgrading, will never bother to add on the ports they know they'll
> never use.
>
> By the looks of your board, I'd say its just had the disc interface
fitted,
> and the extra RAM to make it into a Model B (OS upgrade as well?).

My first Beeb, which I bought not long after they came out, was a Model A,
and it was indeed cheaper to buy the extra bits from a component supplier.

Now that I've looked at Tim's pictures, I can see exactly what's been done
-- and, yes, it's an upgraded A.  Looks like a mid-period Issue 7, so
that's a little surprising, but not unheard of.  Someone has added the
extra RAM, the 74LS163 to drive the sideways ROM selects, the second 6522
VIA for the printer port, the driver and receiver chips and socket for the
RS423, the RGB socket, and the 8271 disc interface.  They've not added the
connectors for the User Port, 1MHz bus, or Tube; they've not added the two
buffers for the 1MHz bus; nor the ADC chip and connector for the analogue
port.

That DNFS ROM isn't an original, by the way.  Acorn did make a few in
EPROMs but most were masked ROMs (201,666 PE02).  It might have been one of
the licensed copies made by HCCS, though.  Being an Issue 7, it would
always have had MOS 1.2 and probably BASIC 2 (B04 and B05 ROMs), and DNFS
1.2 (rather than DFS 0.90) would be right for that era as well.

The other "spaces" on the board are for Econet (top left, in the picture)
speech (two large sockets on the left).

Last point to note:  the video ULA is a real Ferranti ULA, not the later
VLSI VidProc, and it ought to have a heatsink on it.  The lack of heatsink
won't do any permanent harm, but if you get "twinkling" characters after
it's been on for a while and has got warm, that's why.

-- 
Pete                                           Peter Turnbull
                                               Network Manager
                                               University of York