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I haven't tried it on a real Dragon, but the attached example should give something like the effect you're after. (It works on xroar so it stands a chance) It probably needs adjustment to split the screen in the exact place required. It can be a bit of a pain to do any useful work at the same time a...

Are my CPU cycles completely wrong or are my trigger with 17784 cycles wrong? It's hard to say just by looking at the numbers. It's behaving as if (1) a large class of instructions are adding too many cycles to the counter or (2) the irq callback is occurring faster than once per 17784 cycles. Does...

I could have been a bit more clear: I was worried about R2 the resistor, not REG2 the regulator. R2 is located above the ribbon cable. It's 10K (brown-black-orange) on the issue 4 board. I've just noticed R2 is clearly visible in the other issue 3 photo and is 10K there too, so no problem. I'm a lit...

Would that be REG3 (the top one) on my blue Iss3 board? Yes, that's the one. If you decide to have a go at this then you may wish to check the value of R2 which is a load resistor for REG3. It's 10K on an issue 4, but I can't see what it is in the issue 3 photo. Resist the temptation to attach REG3...

Converting from Issue 3 to Issue 4 could be as simple as swapping the 7905 reg for a 7912, if you don't mind losing the TV output. An issue 3 schematic would be useful to confirm this. There is some video level shift circuitry on the issue 4 that seems to be absent on the issue 3. I remember doing t...

That's a really impressive collection. I've been looking at these on youtube and I find 'Pitman' particularly appealing.

Also quite a skill to write action games in Basic. Brilliant!

Great to hear you've got it working and as RWAP also said, it wouldn't be hard to reproduce the PSU board. Though there are alternatives... One of my Dragons, hidden in my attic somewhere, doesn't have a PSU board at all. It's got a switch mode PSU, built in speaker and 3.5" disk drive, but that's a...

I've just been looking at the schematics and photos and it seems to me that issue 3 PSU boards are for D32s and issue 4 boards are for D64s A key difference is the PSU voltage on pin 3. D32s have -5V here and D64s have -12V. Putting the issue 3 board in a D64 shouldn't do any damage but there isn't ...

Now there's a man who is dedicated to his art!

I hope you've saved some surprises for the demo Should drop a few jaws the way things are shaping up...

Could it be because the Dragon ROM checks the MSB of $ff03 is set to confirm vsync is the source of the irq before branching to the TIMER update code?