Sorted by Squirrels.

Tuesday, 15 March 2011

I always use this program as the benchmark test. If you've ever owned a ZX81 then you know what it is. It has such a strong resonance with me. The first time it loaded from tape after the tense 6 minutes of FSK madness it almost stopped my heart. And then I played it.

Fast forward 30 years...

Ladies and Gentlemen.


Allow 28 days for delivery...

See previous post for links to further information.

ZXpand Issue 1

Rex lies in wait.

More details and a draft manual appear on

Monday, 14 March 2011

Making things

I love making things. Tonight I made this thing:

It's a twin ROM switcher, or rather 2 twin ROM switchers, one of which is destined for a C64. JiffyDOS enhanced kernal in one side, regular kernal ROM in the other. SPDT switch added to the pads with a common centre and it's cake time! I'll post a minimal entry when it's looking a little more complete.

I've been making PCBs for a few months now and I'm getting to the stage where I need to start investing in some beginner++ equipment. I have a ghetto UV exposure box that some kind soul freecycled a few years back. It just about does the job but it only has one tube and that makes getting an even exposure hard. You can see on this board that one side is either overexposed, overdeveloped, overunderdeveloped or underoverexposed. Or something. I'll never know, I guess. I suppose seeing that the traces have disappeared then either the negative wasn't pressed closely enough to the PCB or it was overexposed. Reviewing what I did this evening I find it hard to see how I could overexpose one edge like that. That is the mystery and marvel of this process - you have to aim for a zen-like approach otherwise it will end in tears.

Still I think it'll work. I designed this mainly so that I could try out the new PCB material that I sourced. It's a lot cheaper than the usual gear that I score . Even with my relatively inexperienced dabbling I know I have to get a feel for how it reacts to the chemicals. See? Zen again. The design has a lot of traces weaving through the space between pads. It scared me a little while I was eagling it. Ha but now who's the daddy eh?!

Anyway now I've rambled and the board appears to have dried of natural causes I'm off to drill it. Super!

Friday, 11 March 2011

Presenting: ZXpand!

It's only taken me about 3 years.

This is the test fitting of ZXpander prototype 1. You can clearly see that there are some sockets empty. Well, I didn't want to overwhelm the poor old chap.

And yes, it worked! Eventually. After being hacked around so badly that the poor thing's mother didn't even recognise it. It ended up carrying another chip and looking somewhat like Joseph Merrick. But let's not get ahead of ourselves! This was P1, after all. Things are supposed to change. So to P2! Fast forward to only 9 months ago!

My good friend and inspiration Ramoth had been extolling the virtue of programmable logic. He has made the transition to the state of the art while I, comme d'habitude, crept in at the lower, and rather more obsolete level. I decided that I could just about cope with GALs and maybe, just maybe these would provide the answer to my overcrowded board problem! For that is what I had. I couldn't lay out the board to any degree of satisfaction now that 7 TTL chips were required.

So one eBay purchase of the most basic programmer capable of writing GAL fuse maps later, I was dipping my toe into the confusing and contrary world of programmable logic.

The best thing about setting out to work with obsolete technology is the complete lack of any decent documentation and sample code. Oh hang on, that's not the best thing is it. That's the _worst_ thing. Ho hum. Still, after having crawled inch by bloody inch up the steepest learning curve I've ever encountered since girls, I managed to make P2 work.

Here's its good side...

5 TTL chips lighter, this one only required some very delicate hacking...

JESUS! What have you done to it man!

Well it needed some ICSPing. And an extra AND gate. And the 'get it quick' prototype board from PCBTrain doesn't get solder mask, so ... it's not pretty. I realise this. But you know what?

P3 is immanent. Watch this space!

This is how we do it

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About Sir Morris

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Loves: Old computers, Old Techno, Old ladies. Cake.
Hates: New computers.

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