[Parabola]

Thanks for the positive responses. It's certainly possible that I may consider some limited production if I get to the point where it's a further developed product. I'd just need to get my a*se in gear and get some PCBs fabricated commercially.

Originally Posted by Tazman1966

Facinating stuff mister! I imagine that, say, BBC type VITS could be inserted too?

Yep, no reason why not.

Originally Posted by ppppenguin

Well done!

Thanks! You know only too well I'm not a 'natural' when it comes to logic design!

Originally Posted by ppppenguin

Though the concept is simple the problems are all in the detail. There's quite a lot of that to get right.

Absolutely. The biggest problem has been creating a 19 bit counter that's completely glitch free, syncronous (rather than ripple) and can have all the bits reset at exactly the same instant. This resulted in not needing any data latching on the PROM output. It's fair to say some of the counter IC data sheets are not altogether accurate!

Originally Posted by ppppenguin

What sampling frequency are you using? 12MHz like the RT Russell or something a bit higher?

12MHz sampling. I started thinking I'd use 12.5MHz, but if 12 was good enough for Richard Russell it's good enough for me. I also needed to try not to go faster than 70ns or it gets difficult and more expensive to source memory that my PROM programmer can use!

Originally Posted by ppppenguin

What have you used for the USB interface?

Aha! Well, I have a plan for that one if I get to Phase 3, but as I'm going to try and make it all work without any kind of micro or PIC I'm keeping quiet for the time being for fear of total ridicule until I've given it a go. If I should fail with Phase 3, or it becomes too complex to implement, I may adopt a system of plug in 'cartridges' containing PROMs with different images / pages - or even investigate using compact flash cards instead of PROMs / RAM

Finally, as all the parts are available in surface mount versions, it could be built a lot smaller!

Parabola