Unknown 6809 Eurocard SBC

December 2024, Jannie mentions he threw out a Eurocard SBC. Basta, sez I, gimme.

This is what I had to work with. Looking at where the crystal is connected narrowed things down, some further investigation and I know it's a 6809.

Poking at the other chip pinouts and we have 74LS244 and 74LS245 buffers, an LS00 NAND, a '138 decoder, a '30 NAND gate and (this was the tricky one) a CD4011 quad NAND.

Here's what I have for a schematic so far.

So it has space for eight 8k devices, four intended to be RAM and four intended to be EPROM, in that the four RAM devices can be battery backed up but anything goes, really, and any 8k block can be designated as "external" i.e. a read comes from (and a write goes to) the '245 and not the on-board device.

Pity I didn't get an I/O board with it, will have to devise something.