BBC Second Processor Tube ULA (was Re: What kind of IC is this)

[Jules Richardson]

Philip Pemberton wrote:
> Jules Richardson wrote:
>> Not *completely*, AFAIK - although there are fragments all over the 
>> place. I think there's enough amassed wisdom around now that it 
>> *could* be done though, because the software to drive either side is 
>> understood enough, as is the electrical (physical) interface, and 
>> there are still survivors of all the vintage hardware which made use 
>> of the ULA.
> 
> What's available appears to be fairly thin on the ground though. A quick 
> search on 'the bay' revealed tons of Master 128s and BBC Bs, but nary a 
> second processor in sight.

Yeah, I sold a couple on there just over a year ago - pretty much my only 
foray into selling on ebay (and not something I care to repeat). I offloaded 
another four or so via word of mouth. I've got another six Acorn ones with the 
TUBE ULA but as they're all different I don't want to part with them I'm afraid!

> I'd feel a bit bad if I ended up killing a ULA or a 2nd processor though 
> :-/

Yeah. I blew one up by plugging a copro in backwards once and felt guilty (in 
my defence, the silk-screening was wrong on the copro PCB, but I still should 
have checked with a meter first!)

>> The problem is that very few people have both a grasp on that 
>> knowledge and the ability to do the necessary electronic design - it's 
>> only really worth it for a drop-in replacement (i.e. a single chip or 
>> a very small daughter-board to plug into the ULA's 40-pin to DIP 
>> socket) because (as Phil says) it'd be a reasonably large board to do 
>> it as discrete logic.
> 
> Oh, is that a challenge I hear? :)

Kind-of. I figure that a combination of you, Sprow and JGH are probably the 
best three to get something like this up and running... :-)

Sadly all my TUBE docs are in storage*, and I'm not sure what I have scanned 
here with me - I know I've got some TUBE notes from Hugo and a TUBE app note 
(but I think the latter's online anyway).

* i.e. stuff like the A500 manuals might have something useful inside.

> Seems Sprow has a few ULAs left, and one of those (assuming it's 
> working) should be enough to clone the thing, but a 6502 2proc (either 
> cheesewedge or internal, as long as it works on a Master 128) might be 
> handy for a bit of live testing, if such a thing proves necessary.

To be honest, lay out your own 6502 board. I've got schematics and ROM images, 
and there's nowt special to it, assuming you have the ULA.

I keep forgetting to poke Sprow about buying a ULA - I still need one for one 
of my Springboards, and I suspect that the one in my '286 copro might be duff.

cheers

Jules