Donix H5 C5B build

[donix]

Tried to do some scoping on the RESET, AS and A* pins according to the troubleshooting guide and full disclaimer: I am still a bit new to using a scope but I think I did manage to get it to correctly trigger on reset - it does capture the monitored pins after the expected 1ish second delay. However, !AS and A* pins remain constantly high and never go low.

On a whim I checked the HALT pin since I remembered that being eternally high on an earlier occasion and caught it doing this:

halt2MHz.jpeg (590.46 KiB) Viewed 91 times

I can reproduce this and the shape remain the same but the frequency can vary a bit. The bus pull-up on HALT checks out at 1K. Following the schematic it looks to me as the only thing connecting to HALT is U14? Could U14 be dodgy or is there something else on the halt line that I missed?

[exxos]

Normal when the cpu is crashing. You need to do all the tests and not get sidetracked onto other things.

[donix]

Normal when the cpu is crashing. You need to do all the tests and not get sidetracked onto other things.

Thanks @exxos. It is easy to start looking for irregularities at random. The reason for taking stabs in the dark that I didn't really think that I could advance further in the guide. I did follow all the steps in the guide up to and including the first part of the first bus cycle test and on that one I found that neither address line nor !AS ever go low and in that situation I guess that there is no chance of the rest ever working.

Today i got the AT27C4096:s which brought no improvement although they do pop into the socket with a much more distinctive feel. I beeped out all the pins on the CPU PLCC and ROM sockets just to make sure that all are connected and they were. Then I made one more stab in the dark with swapping in the DIP 68K that is intended for my ST booster and lo and behold: The ST starts.

itboots.jpeg (606.86 KiB) Viewed 53 times

The H5 will now work with the DIP 68kP16 as well as with the original PLCC 68k that came out of the STE but it will not with the PLCC 68HC000ET16 that I have available, which was tested in the STE and the twin if which seems to work in the STE right now. But I guess it might be bad somehow...

What a relief though! That was quite a few hours spent down the rabbit hole. Now on to fitting more stuff to the board!

[exxos]

Maybe your CPU has a slightly bent pin or something ? Its normally silly things like that which cause all the trouble. Its why I suggested the Atmel ROMs as the Eproms don't tend to contact very well anyway.

Well done!

[donix]

Maybe your CPU has a slightly bent pin or something ? Its normally silly things like that which cause all the trouble. Its why I suggested the Atmel ROMs as the Eproms don't tend to contact very well anyway.

Well done!

Thanks! It's nice to get somewhere! The CPU pins look good under magnification but it does maybe slide in a tad too effortlessly.