On Jul 16, 18:35, Tony Duell wrote:
> > Yes, I they do (mine has it, and it's shown on all the diagrams) and
now
> > you mention it, it sounds familiar. Or more accurately, I remember
seeing
> > soething about converting US machines back to UK spec (or UK-usable
spec,
>
> Preumably that involves moving the link, replacing the colour subcarrier
> crystal amd replacing the BASIC (and MOS?) ROM?
Yes, and changing the link in the PSU.
> > at least). One Acorn dealer re-imported a lot of unsold US and German
> > Beebs some years ago.
>
> What's a German Beeb? Does it have the QWERTZ keyboard layout and German
> messages in the ROM ? Is that the only difference?
I never actually saw one, but as far as I know, the differences -- if any
-- were very small. I'm not even sure they translated all the messages.
There was a problem with selling Beebs in Germany -- the safety and
emissions regs were tighter at the time than in the UK, and at one point
Acorn wouldn't sanction sales to Germany.
> One thing to emphasise here is that the A and B machines both used the
> same PCB, so upgrading was a matter of adding the extra chips and moving
> various links (for example to enable the ROM select circuitry rather than
> always having the BASIC ROM selected).
Absolutely. And as you point out, you only had to add the things you
wanted, though if you added all the "missing" chips, sockets, and set the
links, there was no way to tell (other than the serial number) that the
machine had started as an "A".
> Real hackers just got the circuit diagram and went off to buy the chips
:-)
Yup. Which is how I discovered that Watfraud's "A to B Upgrade Kit" was
incomplete -- it looked cheaper than the sum of the parts, and when I
looked at the contents I realised why. They had started from the premise
of adding a printer, serial port, RAM, etc; and hadn't realised they needed
little things like the 74LS161 that latches the ROM bank select. I
suspect they'd never looked at the diagram and certainly not been on any of
the Acorn courses, but merely copied parts lists from some other vendors
individual upgrades.
> > Then came the B+. This looked similar from the outside, but had a
> > redesigned PCB with 64K of RAM, some of which was used to "shadow" the
>
> The circuitry was very different in some places, with more ULAs
> (Uncommitted Logic Array chips, basically mask-programmed ASICs). The
> original BBC micro had 2 ULAs, one for the serial/cassette ports
> (included the baud rate generator, cassette modulator/demodulator, etc)
> and one for video (colour lookup table, etc). The B+ had at least one for
> memory control as well.
Actually, that one is a PAL.
> I thought the B+ schematic showed an 8271 disk controller. Or are you
> saying that all B+'s shipped with a 1770 kludgeboard in them.
Not a board; the main PCB has places to fit either a 1770 or an 8271. Both
upgrades (you could buy a B+ without the interface) included a few extra
chips (buffers, etc) but there were a couple in the 8271 kit not required
in the 1770 kit (74LS123, IIRC, and I think one other). The service manual
lists the whys and wherefores; I'll dig it out if you're interested.
--
Pete Peter Turnbull
Network Manager
University of York
Received on Mon Jul 16 2001 - 19:11:02 BST