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While researching this answer, I discovered two East German clones, the Ilmenauer one and this one from Jena. (There is at least one other design from this same region, from Erfurt, I have not looked at yet).

First off, Farbplatine means something like "color board". There is 2x 8K EPROMs on the Grundplatine (motherboard), as expected, and another 2 kilobytes on the Farbplatine, a separate circuit board for dealing with color only.

It has two UB855s on it (East German clone of the Zilog Z80 PIO), which presumably map to the ULA's I/O ports. It has a 555 timer on it to generate the blink frequency.

I believe the RAM on this board is the attributes, which would make this qualify as an answer to my other question on this site. It's possible/probable one of the PIOs stores the border color.

But this question is about the PROM. It's called "EPROM 3 (Farbplatine)" on this page. I can't figure out what it does. Initially I though it might be more software, perhaps German fonts, but now I'm not sure it's even ever mapped to the CPU's address space. It looks like you'd have to go through the PIOs somehow to read it.

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    in the links of yours no circuit, and the EPROM3 contents is blank, and documentation is also not downloadable/viewable so hard to say what it does... we can only speculate it might generate some pattern in border color (without CPU) or produce patterns of attributes to enhance color depth per 8x8 block of pixels ... but all are just wild speculations based on pure hunch...
    – Spektre
    Feb 23 at 10:50
  • Further wild speculation: especially if this clone allows colours to be redefined, the ROMs could be the PAL waveforms for those colours. The Oric is an example of a machine of the era which uses a ROM to generate PAL colour.
    – Tommy
    Feb 23 at 12:13
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    @OmarL storage for SECAM would be the same as for PAL, but I guess wouldn’t add as much value.
    – Tommy
    Feb 23 at 18:09
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    There is, in fact, a schematic for the colour board on the site OmarL linked to: sax.de/~zander/zx/zxj/zxj_fs.pdf. It shows the EPROM attached to the regular address- and data bus, not to the colour generation circuitry. I didn't have time for further analysis, though. For what it's worth, the person who re-drew the schematics in 2013 is still working on that page (last change in 2013), so you might as well drop him an e-mail. Feb 23 at 22:00
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    (That should read "last change in 2021", btw.) Feb 24 at 10:06

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That might be ZX LPRINT III interface, at least it looks like it. IN (#FB) would turn 2kb ROM on and then IN (#7B) would turn it off. You can find more here.

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    Sounds close. From a first glace It's a 2 KiB EPROM mapped in at a 4 Ki address boundary within the ROM address space. But the address might be different as A1..4 must be 1 while A5 must be zero and A7 is used for set/reset.
    – Raffzahn
    Feb 24 at 17:26

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