exxos's Atari, Amiga & retro forum

BrettRogersUK wrote: 26 Jan 2022 16:27 I've enjoyed watching this journey. Really been an eye opener to see what can be done with the proper equipment. Look forward to seeing more! Looks like your making some progress at least looking at those pics from the LA.

Regards,

Brett

:)

It has taken me a long time to acquire all the gear, and be able to repair these things, but thankfully some of it is so much cheaper than it used to be. Don't forget, I am an amateur at this, it isn't my day job and I couldn't design anything electronic for toffee, but I do enjoy it :)

We're still not out of the woods yet, but at least I can see just what is going on at the ROMs.

Bad address = data from the wrong place = CPU going into a /HALTed state. It all adds up, but more work to be done, at least I have a target now.

rubber_jonnie wrote: 26 Jan 2022 16:32 :)

It has taken me a long time to acquire all the gear, and be able to repair these things, but thankfully some of it is so much cheaper than it used to be. Don't forget, I am an amateur at this, it isn't my day job and I couldn't design anything electronic for toffee, but I do enjoy it :)

We're still not out of the woods yet, but at least I can see just what is going on at the ROMs.

Bad address = data from the wrong place = CPU going into a /HALTed state. It all adds up, but more work to be done, at least I have a target now.

You've got further than me. I just hit a dead end because I hadn't got the hardware to test it to find out what you've found. I look forward to seeing your progress.

Regards,

Brett

BrettRogersUK wrote: 26 Jan 2022 16:38
You've got further than me. I just hit a dead end because I hadn't got the hardware to test it to find out what you've found. I look forward to seeing your progress.

Regards,

Brett

For stuff like this, you do really need the gear, or you have no idea what's going on. There was a time when I wouldn't have attempted it, and there is still so much I don't know, but weirdly, this is fun for me :)

Well, with the knowledge you have now you could definitely design digital electronic stuff. It's basically electronic Lego. You just need to know a few rules of thumb really about bypass caps, pull-ups and basic logic (and gates, inverters, not gates etc.). It's mostly, "if you do this, that happens".

Even the basic timing stuff isn't that hard. e.g. if you need a delay between /CE and /OE pass the /CE through a couple of inverters to delay it a few nanoseconds and Bob's your Aunty. (With memory (ROMs and SRAM) you have to remember that /CE primes things, getting everything ready and /OE just opens the gates to let the data in/out.)

rubber_jonnie wrote: 26 Jan 2022 16:41 For stuff like this, you do really need the gear, or you have no idea what's going on. There was a time when I wouldn't have attempted it, and there is still so much I don't know, but weirdly, this is fun for me :)

Indeed. Without the correct tools you get nowhere. Once you have them it's just a puzzle where you follow the clues, which is the fun/infuriating bit.

stephen_usher wrote: 26 Jan 2022 16:43 Well, with the knowledge you have now you could definitely design digital electronic stuff. It's basically electronic Lego. You just need to know a few rules of thumb really about bypass caps, pull-ups and basic logic (and gates, inverters, not gates etc.). It's mostly, "if you do this, that happens".

Even the basic timing stuff isn't that hard. e.g. if you need a delay between /CE and /OE pass the /CE through a couple of inverters to delay it a few nanoseconds and Bob's your Aunty. (With memory (ROMs and SRAM) you have to remember that /CE primes things, getting everything ready and /OE just opens the gates to let the data in/out.)

You know maybe I should just try!!

@rubber_jonnie Go on - you know you want to!

:poke: :hide: :fire: :fire: :fire:

JezC wrote: 26 Jan 2022 17:56 @rubber_jonnie Go on - you know you want to!

:poke: :hide: :fire: :fire: :fire:

Not you too!!

I'm feeling like a minor celebration. I traced A1 and found that it should be connected to pin 2 of the DMA. Only it wasn't, so I hooked it up and I now get this:


Which I am going to take as progress since it looks like something is getting to video RAM, something I'd not seen before.

Clearly some work left to be done, but the little red led on my diag cart which shows ROM access is now flickering, a good indicator that ROM access is at least being tried. It was completely dead up until now.

Clearly something is going on and it is trying, so more checking to be done, I'll need to look at A2 next.

I also added some test points near the GST combel and I can see that A1 & A2 are connected all the way from there to the Blitter, the CPU and finally the ROM and A1 to the DMA. I am also seeing address line pulses all the way through now too.

More to do though, @exxos another one for your crash screen archive :)

Nice! Test cartridge run yet ? :hide: