Date   : Wed, 26 Mar 2003 21:37:35 GMT
From   : Peter Turnbull <pete@...>
Subject: Re: BBC Micros, what else :)

On Mar 26, 15:21, Kate Kneebone wrote:

> They do have different power supplies, neither of them black ones.
 If
> the stickers on the back where the power switch is are to believed,
one
> was made by Wong's Electronics in Hong Kong and the other by a
company
> in the UK (may well be BSR). So is it a bad idea to plug things into
the
> power socket underneath the computer then.

No, mostly they're OK, certainly with single drives.  Some of the older
dual drives are a bit more power-hungry; it might be worth checking the
label to see if it mentions the current rating of the supply.

>   > If you remove the PSU, *make sure*
>   > it's unplugged from the mains first [...] Keep your fingers out
>   > of the PSU

> Yep, I'm very wary of stuff like that.  Particularly after an
> embarassing incident at work where I picked up the backlight power
board
> for an LCD display that was turned on and blew a little hole in my
> finger :(  LCDs are now Kate-proofed with plastic bags :)

:-)  I've also been bitten by an LCD supply (which are fortunately
quite low power), and attacked without provocation (well, not much) by
a Beeb SMPSU I was repairing.

> On a whim I decided to take a bottle of whiteboard cleaner home last
> night, and while it's absolutely hopeless at getting the yuck off our
> whiteboard, it's great for cleaning BBC micros with!  Apparently it's
> also exactly the right thing to use to remove the ink but not damage
the
> plastic (I knew being related to an organic chemist would come in
handy
> at some point!).

Yes, most of those cleaners contain some IPA, and some other gunk.

>  > BTW, I wouldn't make it
>  >bank 15 because that's the most significant bank, and if you ever
get a
>  >corrupt image in it, you need to switch the Beeb off to clear it,
>  >whereas if it's in a lower priority than BASIC you can always get
>  >control back with BREAK and write zeros into the RAM.  Mine has a
>  >little 2-way with centre-off toggle switch fitted, wired so that up
is
>  >"write protect", down is "disabled", and centre is "normal".
>  >
> Hmm, I'd not thought of that.  If BASIC's ROM 15 then it looks like
I'm
> imagining how things work wrong.  I was thinking that the four ROM
> sockets counted up from 0 going left to right, but from what you've
said
> it looks like I've actually got it completely wrong.  I think I've
> probably missed some inverters somewhere.  So the ROMS are actually
> 15-12 counting down right to left then?  If I put my RAM in the
socket
> to the left of BASIC then that would indeed mean my RAM would appear
at
> 0b1110, 1010, 0110 and 0010.  I think I understand now!

Both the Beebs I normally use have ATPL sideways boards, but of the
ROMs on the original board, left is lowest, just as you said.  If you
have a sideways board fitted, and use QC and QD of IC76, then the four
sockets on the original board are 0-3.  If you don't use QC and QD,
then their values are "don't care" and of course the same devices are
seen at 0-3, 4-7, 8-11, and 12-15.   Then, as I said, the MOS discards
duplicates, so in effect you end up with the ROMs being seen at 12-15.
 Anyway, the MOS keeps track of which language ROM is highest, which FS
ROM is highest, and keeps a single reference to each ROM.  IIRC there's
a block of 16 bytes in zero-page with the ROM type bytes, and you can
disable any ROM by zeroing the corresponding byte.

> Hmm, I'd rather not do any soldering to the computer itself.  The
> potential to destroy one of the finite number of BBCs still around is
> too much for me!  If clipping the leads on is horrendously
un-reliable
> then maybe I will though.

Well, Beebs aren't *that* rare, and the risk isn't that great if you
have a little practice, use a decent soldering iron, and thin wire
(wire-wrap wire is good).  You have to start somewhere if you're going
to be a hardware hacker :-)

-- 
Pete						Peter Turnbull
						Network Manager
						University of York