interesting machine. the paper roll graphic display could make for a cool retro tech display in a moody movie, a la the scene in mr robot with the C64 and Angela.

The first board ('board 1', with the bad battery, it doesn't seem to have a marking on the silkscreen) seems to be I/O, and peripheral to the other board.  It has 4 KiB RAM, and 32 KiB ROM, but much of that is data.  The admixture of 8255 and Z80PIO is striking.  8255 were cheaper and simpler, so it seems if they used a PIO then they might have done that for a reason.  But since 'board 1' seemed to be peripheral, and because I do not have schematics, I dug a little deeper into into 'board 2'.

'Board 2' (silkscreen "MCU02") seems to have a 24 KiB rom system in roms marked 1-3.  These are mapped at 0000h-5fffh.  8000h-ffffh is the DRAM.  6000h-77ffh is, I suspect, the static ram in chips marked IC130,137,143.  That region is init'ed in two chunks -- one of zeros and the other of spaces.  Interestingly, there seem to be parallel chunks in system RAM at e000 and e800.  This is striking since the sram should otherwise have read/write access.  IC129 is surely the character generator rom, but as it's soldered in I suspect a dump is not forthcoming.  No matter, it's not required, but may be useful eventually understand how the Japanese characters are depicted.

There is a 2 KiB hole at 7800h-7fffh.  And there is an invocation to 7800h.  I'm not yet sure if this is for the ROM cartridge, or for 'rom 4'.  'rom 4' is interesting in that it is 4 KiB, but half is unused.  It /could/ fit there.  But it also seems to be a boot rom.  In the photo, it's close to connector CN109.  Maybe it's a 'default' cartridge?  (and maybe I'm barking up the wrong tree.)

The MCU02 does not seem to use NMI, but does seem to use INT, and in the Z80 IM1.  This is striking, because I do not (yet) see an explicit switch to IM1 in the code of roms 1-3.  So maybe rom 4 does that before paging out.  Perhaps I should have a word with rom 4...

I did find the BASIC error code display routine, which should make short(ish) work of resolving the display stuff. It’s been a while since I saw a 684x.