Well, I had seen a post on vcfed about using an EEPROM as a PROM :
https://forum.vcfed.org/index.php?threads/rep … h-eeprom.64656/
82s181 seems to be drop-in replacement of my MMI 6381 one, and it's just connecting pins, noting much, so the only problem is the code for the EEPROM.
Well, I got some M20s ROM dumps from emulator, they're not labeled, so maybe there is the one I need.

mouser & digikey seem to stock that AT28HC64B.
seems like the tl866 programmers can program those.

fyi, digikey also stock the AM27S281APC which looks like a direct replacement, though the tl866 programmer doesn't program it.

options enough , just need the data.

I have found one seems-compatible EEPROM in my stock, so we will see, I'll make an adapter for that and see if it's character generator or something else

So, I have found that PROM on the M20's schematics. (HW2 page 51) and that's indeed memory mapping PROM, so I have problem now...

So I have made an adapter to use EEPROM instead of that PROM and it is not working in the same way it was, so I guess that's good. The problem is that 6381 PROM got 4 Chip select lines, and that eeprom only 1. Got in touch with a person who built a M20 clone, and he said that M20 uses 3 out of 4 CS, and it won't be possible to use some expansion cards with that EEPROM2PROM thing.

I saw on vcfed you found the data.
The AM27S281APC is still available on digikey, then you'll just need to find someone who has the equipment to program it.

weedeewee wrote on 2022-11-10, 13:17:

I saw on vcfed you found the data.
The AM27S281APC is still available on digikey, then you'll just need to find someone who has the equipment to program it.

I have a Hi-Lo ALL-03 at hand. The documentation says that it supports the AMD 27S280/281/281A. If get an AM27S281A shipped to me, I can program it and send to you. If you live outside Europe, I would appreciate if you support me on the shipping costs. Get in contact with me privately (you should have enough posts for using PMs) if you want to accept that offer.

mkarcher wrote on 2022-11-10, 22:41:

weedeewee wrote on 2022-11-10, 13:17:

I saw on vcfed you found the data.
The AM27S281APC is still available on digikey, then you'll just need to find someone who has the equipment to program it.

I have a Hi-Lo ALL-03 at hand. The documentation says that it supports the AMD 27S280/281/281A. If get an AM27S281A shipped to me, I can program it and send to you. If you live outside Europe, I would appreciate if you support me on the shipping costs. Get in contact with me privately (you should have enough posts for using PMs) if you want to accept that offer.

mkarcher, You're replying to the wrong person. :-p
oh and bernkastel7734 lists his location as poland.

Bernkastel7734 wrote on 2022-11-10, 13:08:

Bernkastel7734 fyi, I've become uncertain if you need a 27s281 or an 27s280. the difference being the one's output can go Hi-Z. though maybe that doesn't matter.
I should go to sleep. goodnight.

Yup, I'm in Poland.
So, M20 works but is very unstable. Sometimes it boots, sometimes it shows RAM Errors.
So, M20 is compatible with MDA monitor, but you need a monitor with VHold and HHold potentiometers.

bernkastel7734, what chip did you now use to fix it ?

Instead of 6381-2 I am using 27C1001

I have no idea what's going on, but it works only if there is light shining at that UVEPROM window

Wow that is is good that you at least can get it to boot and see the screen. Odd behavior for a UV eprom......

It can be any source of light, any color of LED, LED bulb or even my phone flashlight

I'd try other eprom, but that's the only 55ns or faster than I have