exxos's Atari, Amiga & retro forum

stephen_usher wrote: 27 Jan 2022 18:48 Here's the demo of the POST card. S1 isn't reset unfortunately, I've no idea what it does, maybe nothing on the ISA bus.

Hmm, interesting, I presume aside from the multi press reset to start, it's showing all good voltage wise?

Wonder if those QS8888's will work!

Yep, all the voltages are fine and once the machine does reset properly it's bulletproof.

Soft resets work fine, so Ctrl-Alt-Del works as it should. It's only a hard reset which is a problem. I may hoik the CPU out and check what's happening on the RESET pin. According to the spec. it should stay high for at least 15 clock cycles to reset the CPU. For 33MHz that should be about half a microsecond, I think.

As for the chips.... You wait three weeks for one and then five come at once. ;-)

stephen_usher wrote: 28 Jan 2022 13:58 Yep, all the voltages are fine and once the machine does reset properly it's bulletproof.

Cool.

stephen_usher wrote: 28 Jan 2022 13:58 Soft resets work fine, so Ctrl-Alt-Del works as it should. It's only a hard reset which is a problem. I may hoik the CPU out and check what's happening on the RESET pin. According to the spec. it should stay high for at least 15 clock cycles to reset the CPU. For 33MHz that should be about half a microsecond, I think.

Does soft reset operate in a slightly different way to hard reset? Could the hard reset circuit have a failing IC?

stephen_usher wrote: 28 Jan 2022 13:58 As for the chips.... You wait three weeks for one and then five come at once. ;-)

Bit like (data/address) buses then..........

Apparently, on the 486 there are two reset pins, RESET for hard reset and SRESET for a soft reset. I'm guessing that Ctrl-Alt-Del uses the latter.

stephen_usher wrote: 28 Jan 2022 14:24 Apparently, on the 486 there are two reset pins, RESET for hard reset and SRESET for a soft reset. I'm guessing that Ctrl-Alt-Del uses the latter.

Oh, that's interesting. Wonder what the differences are then.

stephen_usher wrote: 28 Jan 2022 14:41 486-reset.png
486-sreset.png

So then the majority of the reset remains the same with the exception of that register?

Looks that way. I would have suggested putting SRESET first in the sheet and had RESET as being, "As SRESET but also clears xxxx register." :-)

stephen_usher wrote: 28 Jan 2022 15:00 Looks that way. I would have suggested putting SRESET first in the sheet and had RESET as being, "As SRESET but also clears xxxx register." :-)

Yeah, would have made more sense.

I've got the chips home and suspiciously they all have the same date code, but different markings on the underside. The writing isn't quite the same as the original chip either.

The pins show that the chips have been pulled from sockets.

Well, there's one way of finding out if they work...