General Stuff(tm)

[PhilC]

Good that the ram is now stable, that's annoying about the keyboard.

[stephen_usher]

Yeah, and "load" programs aren't loading from tape but short ones are. Possible bank switching issues as well?

[rubber_jonnie]

Yeah, and "load" programs aren't loading from tape but short ones are. Possible bank switching issues as well?

Doesn't sound like you're having much luck with it!

What looks after the bank switching and how does the machine determine which bank the code goes into? I presume it bank switches anything above 64KB or is it anythig over 48KB?

I'm sure it isn't, but have you tried a different ROM, the original one I made for my Enterprise cause a ton of weirdness and it was fixed by burning a new ROM.

[stephen_usher]

This is probably why the bus isn't getting held up correctly... The cursor signal from the 6845 never overlaps with the pulse allowing the 4538 to raise the bus request line. They miss by about 2.8uS.

IMG_5418.jpeg (172.66 KiB) Viewed 44 times

@rubber_jonnie I've tried rewriting the ROMs but there's only one set of images I can find on the Internet.

From what I can work out the bank switching is done using an I/O port. On the 96K it swaps the ROMs in and out and overlays memory on top of those addresses.

[stephen_usher]

I've got back from my partner's nephew's wedding weekend so had a chance to catch up a bit.

Ian Cudlip tested his machine and the keyboard, according to him, works perfectly and there's nothing on that specific 4538 output either, so that's a red herring. This is why you always need a reference machine.

It has been suggested to change the ROMs. So I downloaded the ROM images from a completely different site and wrote new EPROMs, ST M27C512 instead of the Winbond W27C512 EEPROMs. The ROM images turned out to be identical. After swapping the ROMs the symptoms didn't change.

[rubber_jonnie]

I've got back from my partner's nephew's wedding weekend so had a chance to catch up a bit.

Ian Cudlip tested his machine and the keyboard, according to him, works perfectly and there's nothing on that specific 4538 output either, so that's a red herring. This is why you always need a reference machine.

It has been suggested to change the ROMs. So I downloaded the ROM images from a completely different site and wrote new EPROMs, ST M27C512 instead of the Winbond W27C512 EEPROMs. The ROM images turned out to be identical. After swapping the ROMs the symptoms didn't change.

Well it was worth a try, I can only assume that my ROM IC was bad, it's been fine and dandy since I replaced it. Shame it didn't work for you.

[PhilC]

Wondering if the rims are too fast? I know the Beeb has issues with newer eproms.

I burnt my new rims onto a three 200ns eproms that I had and it has ran fine so far.

[stephen_usher]

Well, after basically rewriting the lynx2wav conversion program I've at last got a working version of the "Jet Set Willy" 96K port and it works.



Well, other than the keyboard issue and random (but relatively rare) display memory glitches.

It proves that the memory paging is working as is most of the machine. The video memory glitches are probably another symptom of the timing problem causing the keyboard issue.