68HC000 (and other MSTE CPU) oddness

[displaced]

Hi!

I swapped the MC68000FN-12 in my MSTE for a Mc68HC000-FN20. Does indeed run much cooler than the original, which is uncomfortable to touch for more than 5 sec or so even at 8MHz.

All seemed well - GEMBENCH looked good on loop, YAART ran for ages. All great.

But then I noticed a large amount of games (ppera's collection) failed to start. The RUNME.TOS would just hang with a stuck cursor at the top-left.

Initially I thought it was a bad SD card in my UltraSatan, but same problem with a fresh one.

Swapped back to the original CPU and everything's fine. Guessing this is just one of those things?

That's all understandable. But here's an odd thing. I've got a donor STE board that I was messing with. That's got an STMicro TS68000CFN8 in it, which I assume is an 8MHz part. But this runs at 16MHz in my MSTE and stays really cool all the time, even at 16MHz.

Is this just a binning quirk? A difference between the MC and STMicro part? Maybe no explanation is to be had, but thought it was interesting. I'm going to leave the STE's CPU in the MSTE and see how it behaves for a while.

[exxos]

CPUs will drive you nuts. From MC to ST Brand , one will causes DMA issues on the STE and the other won't, even though they are basically the same chip.

I didn't spot any issues on the MSTE with the HC CPU, but like on the STE, the HC CPU adds more capacitive loading on the bus whereas the NMOS tends to float high and aids poor bus pull ups. Plugging in a cartridge can cause a machine to work or not work as another example.

So its often wrongly assumed the HC CPU is to blame, when in fact its just showing up problems with the machine. Just because the system works now with the original CPU doesn't mean it will continue to do so in the future.. If swapping to a HC causes issues, then its time to start modding the machine and doing some servicing. This type of issue is well known to happen on the STE. Its why my STE boosters have pullups on the bus and why I always recommend changing bus pull ups to 2.2k now.

[displaced]

Thanks for the info -- these things really were pretty much barely working even from new, weren't they? :lol:

I'll find out what I need to know about swapping those pullups!

[exxos]

Thanks for the info -- these things really were pretty much barely working even from new, weren't they? :lol:

Exactly !