This is how it looks:

mbertheau2 wrote on 2025-12-13, 22:10:

Then with some trial and error, and looking at how other RTC chips are implemented, maybe I can figure out how to talk to it. It's interesting that the RTC chip has only 4 data lines connected to the data bus.

The 4-bit interface rang a bell, I've seen that somewhere. Turns out I remembered the Euro PC, which uses a EM Microelectronic M3002 RTC chip, likely a successor to the M3000. You can find the datasheet for the M3002 online. which may (or may not) help understanding the M3000. Your battery circuit looks strange (battery power only injected in pull-up pins). I suggest you verify whether the circuit on the card matches the "low battery current circuit" application example as shown in the M3002 data sheet.

mkarcher wrote on 2025-12-14, 23:25:

Turns out I remembered the Euro PC, which uses a EM Microelectronic M3002 RTC chip, likely a successor to the M3000. You can find the datasheet for the M3002 online.

Wow, that's super promising! I'll try to talk to the M3000 like it's described in the M3002 datasheet.

mkarcher wrote on 2025-12-14, 23:25:

Your battery circuit looks strange (battery power only injected in pull-up pins). I suggest you verify whether the circuit on the card matches the "low battery current circuit" application example as shown in the M3002 data sheet.

I'll verify that, thanks! I'm still not definitely finished with the schematics.

Indeed, if programming is the same as for the M3002, you can copy the EURO-PC BIOS code to write a driver. I have disassembled the relevant sections, see here
Re: Schneider Euro PC

You only need
- RTC read at sub F000:EF66: Byte to be read submitted in CL. Result in AL, CF=1 on error.
- RTC write at sub F000:E952: Byte to be written submitted in CL. Value in AL.