Does it look like like apps crash on their own when already running, or just get corrupted during loading? Because that might help narrow down the culprit. If the apps crash or glitch over time while running it's most likely RAM. Bad, or something wrong with refresh. On the other hand if loaded programs seem fine but crashing occurs while trying to run something, or go back to OS, it's something related to disk I/O.

Disk I/O can also be sort-of verified if you have a floppy controler and HDD, try the other one and see if that helps any.

It looks like corruption when they are getting loaded... the results vary, but usually end up in graphics (e.g. sprites), or programs giving odd, unexpected errors.

Interestingly, this problem doesn't seem to occur when I create the CF cards using the serial over XTIDE. Maybe the writes don't trigger any issues.

I don't have any other IO method right now. I will need to go out and find something 😀

Thanks for the suggestion.

sounds like ram. which kind of ram did you end up using? the PLD or no PLD?

Hi, The board uses SRAM (AS6C4008). This has tested fine using checkit, but I have ordered 2 replacements, just in case.

I have installed the optional ATF16V8 (SPLD) to support UMBs, and I've got the DIP switches set to allow UMBs at 0xD0000 through to 0xEFFFF. However, nothing is loaded UMB.

Have tried swapping out the PSU for another, and moving the XTIDE CF card to another address. Sadly, none of these make a difference.

The DOS edit command will frequently just hang after running it. I guess this still points to either memory or IO.

What are the markings on your CPU? The speed grades of 8088s can be a bit non-intuitive.

It's a V20... D70108C-8

I'm running it at 4.77Mhz. The higher speeds seemed to make the instability worse.

Hmmm, now the original 8088s had a rise time requirement on the timing pulses which meant you effectively needed a higher rated chip to run at 4.77 on a square edged clock pulse at 50:50 mark space ratio... Orrr.... have a clock pulse massaged into something it would accept better which is like trapezium shaped pulses at about 40:60... otherwise the lowest speed part can only run at 4Mhz or something (Maybe that was the deal with the Junior to use cheaper CPU and clock circuit) ... but you'd think V20s would be so done with all that crap.

You would have thought so... the docs claim the early V20s ran at speeds of 5, 8, and 10 MHz.

Ah, half remembering stuff, so the 8088 needs a 33% duty cycle clock due to having a minimum clock low requirement, whereas a V20 can use a 50%... See some explanation and discussion here... https://hackaday.io/project/170924-v20-mbc-a- … mebrew-computer

But I'm thinking that a clock intended for 8088 might not have the minimum high time for the V20... but that works out 7 and a bit Mhz equivalent pulse shortness, so an 8Mhz should handle it... maybe, unless it's confused by duty cycle, or the rise times are too long and shorten the effective high pulse to something it can't quite register.

Interesting that you raise that... I found this little note tucked in the build instructions:

The recommended CPU is 10 MHz 8088, for example AMD P8088-1, or Siemens SAB 8088-1-P […]
Show full quote

The recommended CPU is 10 MHz 8088, for example AMD P8088-1, or Siemens SAB 8088-1-P

• Possible replacements are 10 MHz or higher NEC V20 (μPD70108C-10) or NEC V20HL (μPD70108HCZ-10, μPD70108HCZ-16)

• 8 MHz 8088-2, 80C88-2, and NEC V20 (μPD70108C-8) parts might work as well

So, I currently have the 8 MHz V20... but the 10MHz version might work better. I will try and find one and let you know if it makes any difference.

For anyone that is interested, just thought I would provide an update on my micro 8088 board.

I ended up replacing both the RAM and CPU (with a V20 @ 10MHz) without any noticeable effect.

However, when I replaced the CF card with a "known good" Toshiba one (branded "Cisco"), then everything started to work.

Turns out that with XT-CF, the CF cards fall into 3 distinct categories:
1. Those that don't work (these are obvious, they just don't work and you know about it very quickly)
2. Those that look like they work, but don't really (e.g. ending up in data corruption, etc)
3. Those that work (these seem to be harder to find).

Thanks to everyone that pitched in with ideas.

Gotta respect the hours put in by Satan's tech department coming up with all this stuff that almost works, sending you round in circles and driving you mad for days 🤣

Yeah, so true. It's somewhat funny in retrospect, but I really did go round in circles on this one for days.