On Jul 15, 20:13, Tony Duell wrote:
> Hmmm... I have the US Beeb schematic somewhere.... OK, found it.
>
> The US version of the Beeb can output NTSC video.
> Having found the US Beeb schematic, that's what they did, almost. The
> cystal is 14.318MHz, and there are a couple of other capacitor changes in
> the oscillator circuit. The flip-flops are re-numbered (IC46 -> IC96 and
> IC44 -> IC97) but the circuit is unchaged electrically. And the output of
> IC97b goes to one side of link S32. The centre pin of the link goes to
> the xor gate input (now IC99d), the other outside pin is grounded. Set
> the link one way and you have PAL, set it the other way and you get NTSC.
> I think all BBC B+ machines have this link as standard (even the UK
ones).
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,
at least). One Acorn dealer re-imported a lot of unsold US and German
Beebs some years ago.
For readers unfamiliar with the BBC family, the original machines were the
Model A and Model B; the A lacking certain components present in the B to
provide multiple-ROM support, printer port, user port, serial port,
analogue port, 1MHz bus or Tube (2nd Processor) ports, and only having 16KB
RAM instead of 32KB. However, upgrading was easy (and both official and
unofficial kits were readily available) and there was no difference at all
between a B and a fully-upgraded A. Both could be further extended with a
disk interface, proprietary network interface, and various third-party
addons.
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
screen and OS workspace. There was a 64K upgrade for it, which made it a
128K machine (though you couldn't actually do much with the extra RAM
except put BASIC and it's variable space in it). It also used a 1770 or
1772 disk controller rather than the 8271 in the B (though you could fit an
8271 to a B+ or a 1770 to a B).
That was succeeded by the Master 128 -- externally as well as internally
different. It had a numeric keypad added, used double density disks by
default, had two ROM cartridge slots, more comprehensive MOS (machine
operating system), several utility ROMs that would be extras for a B/B+
were built in, and it used a CMOS 65C02. It also used more custom chips
:-(
There were some coprocessor addons for the 128 and other members of the
family launched shortly after it, like the Master Compact (a two-box
solution) and the ill-fated Econet Terminal (terminal and network software
only, no BASIC and no extra interfaces, didn't sell well and was quietly
dropped).
After that, in 1987, came the Archimedes range, based on the ARM processor.
Initially the A310 with 1MB, which still had red function keys to denote
its standing as a BBC Microcomputer, then the A440 (grey keys, not a BBC
Micro). And after that, the A3000 and its successor the A3010, which were
the last with BBC endorsement and once again were single-box systems (like
an Apple ][ or Amiga 500, etc). There were many other models in the
ARM-based range, ending with the RISC PC, but none were BBC Micros.
Despite all this, when someone refers to "a Beeb" they usually mean a Model
A or Model B, not a B+ or later.
Acorn trivia: the plastic case of the A3000 was deemed not strong enough
to support the weight of a multisync monitor, so a sheet-metal stand was
devised. The front of it sat on the strong edges of the A3000 case, the
rear was supported on a bent-over section. Because it clung to the case,
and from the front looked like the outline of a Klingon warbird, it became
known as "the klingon".
--
Pete Peter Turnbull
Network Manager
University of York
Received on Sun Jul 15 2001 - 19:56:28 BST