Date : Sun, 08 Feb 2004 21:03:01 +0000
From : Richard Kilpatrick <oldcomputers@...>
Subject: Re: Tube ULAs
On 8 Feb 2004, at 20:35, Jules Richardson wrote:
> Silly one, but does the 286 board have a fuse on it (as the 6502 copro
> cards do)?? There may be other voltage regulation on there too for the
> memory which is worth a check...
No fuse. Already gone for the obvious ones :)
> Any chance of the photo of the board? Never seen a 286 one.
I could have sworn I sent you one with the Mouse board (it's definitely
a mouse board, the two main chips are THCT (I think) counters.). I'll
send another. Actually, it's online at my retrotech page in a slightly
smaller form.
> well double-check cabling and power supply lines for starters. Re-seat
> any socketed chips. Check power supply voltages.
Done, done, done (4.87V).
> Far as I know it's dedicated to the particular 2nd processor and not
> independant :(
It's not. Both the 32016 in the ACW and the Z80 also have the same ULA.
So I swapped the one from the Z80. No difference, Z80 still worked, 286
doesn't. Bah. I can blame part of this on my ABC which has a baffling
problem, it doesn't seem to see 'all' of the installed ROMs - for
example, I have almost the exact same setup at present as my ACW - all
links east, BOS ROM top right, then the BBC B+ Language/OS ROM, then
ADFS (Acorn ADFS instead of 'ACW ADFS' as you get on the Cambridge,
DNFS (xxx666 non-EPROM type) centre lower row. No startup beep, no DFS
when I boot/ctrl-break with D - yet BOS ROM in ACW (the only wildcard
in the lot) behaves exactly as it should. I can only assume the I/O
board has a fault of some sort, I've checked all the power connections
etc. Can't see SRAM either.
Regardless of these problems (I wondered if the apparent lack of ROM
visibility would prevent the Tube code being read), it's not working
connected to a BBC B+ 128K either, which I /know/ has all the required
ROMs.
> Or a code for 512kbit devices maybe??
Possibly - it was more the date that I was amused by, the rest of the
machine is clearly 1984.
> Oh gawd, if that's the sort of socket I'm thinking of, leave it well
> alone. Those things are a pig to sort out once you take the IC out,
> without bending pins, breaking contact pads on the IC etc. (grrr!)
It's just 'flat'. Seemed quite inoffensive to me actually, I carefully
dropped the IC back in place and clamped it down again. Made no
difference to what it was doing ;)
> Well if it isn't the ULA, and the ROMs aren't toast, then anything else
> can be fixed...
That's my thought, though at that point it is beyond my skills, I think.
> Pull the roms on it and back them up before you cook them :-)
I don't have an EPROM burner/copier. It's on my shopping list ;)
> I'm still missing a BBC 32016 copro board (as opposed to the 4MB one in
> the ACW) and the 286 board like yours (although was it ever offered as
> a
> BBC copro, or only in the ABC machines?).
Only the ABC, as far as I am aware. I don't have an external Scientific
co-pro, but then, who needs one when you have a Cambridge :)
> Oh, there was an ex-Acorn guy
> on the classiccmp list a while back who'd built a 6809 copro back in
> his
> day... don't think it ever made it out of the lab though...
I've read about third-party 6809 - it was a common CPU at the time,
after all, and Commodore offered it as well as the Dragon 64?
In answer to Mike's points - I don't have any VLSI ULAs, only 9Cs, and
yes, it was the same. The ABC lacks CMOS (and ex/intube) commands, as
it's basically a BBC B+ with upright connectors and headers for the
internal video added, and generally they have Econet. Chris at 8bs got
one of the boards once and was very confused by it, choosing to make a
BBC B with it!
As for the co-pro, I took the CPU out and looked at it, and it is a 286
for sure.
The ABC lacked a language ROM when I was given it. I suspect it has
been pillaged, kludged and generally mistreated for a while, I cleaned
emulsion paint off the case - the owner had a working one and this one
has rested in a garage for a while, lacks a keyboard, and lacked an HD.
I originally just wanted them to fix the case on my ACW and out of
curiosity. Is this the point that I admit that I have an ACW because I
wanted a 'nice all in one BBC that I could put in the studio, drill a
hole in the case, add a 1/4" audio jack and use it for speech
sampling'?
Needles to say, that /didn't/ happen ;)
Richard
--
Richard Kilpatrick
Older than most of his computers, but not by enough to know better.
Acorn: '82 to '98. Atari: '79-84. Apple: '84-04 (no Apple //, for
shame!).
http://www.dmc12.demon.co.uk/retrotech/