Date : Wed, 20 Dec 2006 11:45:24 +0000
From : pete@... (Pete Turnbull)
Subject: Curse of the long TUBE cable
On 20/12/2006 09:03, Richard Gellman wrote:
> So, one quick cable change later and... nothing. No fault or anything, it
> just doesn't "activate". I still get the standard issue "BBC Computer
> 32K". Its as if the cheese wedge wasn't even plugged in.
[ ... ]
> I'm told that strategically placed line drivers on the TUBE lines might
> resolve the problem, but this is not a guarantee. I'd be interested in
> people's thoughts on getting it up and running. As far as I can tell the
> cheese wedge board has suffered no ill fates.
My memory could be failing here but I seem to recall there being
something odd about the polarity of that cable (like it not being
obvious which side is pin 1 at each end). Are you sure you haven't got
it crossed over? Or if there's a transition header on the 6502 end,
have the tines failed to make a good contact with the new ribbon cable?
I have a Z80 2nd Processor board piggy-backed (daisy-chain fashion) on a
6502 and the extra cable length has never been a problem, so I doubt if
it's the length that's the problem providing it's still reasonably short
(300-400mm).
> As mentioned, using a shorter lead is physically impossible due to space
> restrictions (the wedge needs to sit off to the side somewhat). I don't
> want to wire the board in internally as I'd like the option to switch the
> board off as required. This could be done by hacking a switch onto the
> TUBE NCS line, but I'd prefer a more elegant solution.
The solution I used for my Z80/6502 combo was to power them from the
Tube interface. You'll find there are some links on the 2nd Processor
boards to enable that, and if I recall correctly there are places to fit
Molex shunts to provide those links. I wired a centre-off two-way
switch so that I could power up the Z80, the 6502, or neither.
--
Pete Peter Turnbull
Network Manager
University of York