How do you solve an extension problem ? Get more extensions ! I found a couple more Nanoréseau adapters on classifieds:

It's interesting to know that the Nanoréseau required quite a lot of RAM so each adapter comes with a memory extension (64KB). I have already seen this extension in a MO5 computer as a "hack", where the cartridge port was removed to integrate the 64KB PCB inside the box. One can see the 4164 DRAM chips, 2 of them are enough to create a 64KB block.

This is very interesting indeed.

One important aspect of this project is to create new extensions. Now I can measure the physical dimensions (bring the caliper !) to make compatible cartriges as well.

I already had small ROM cartridges and I can compare with them.

(pictures here)

I also found a "game port extension" that contains a 6821 that drives a 6-bits R/2R DAC and a couple of switch-based joysticks. Note that the board contains no address decoder, isn't it interesting ? :-)

By cutting the middle connexion, we can get the 6821's ports and hook 16 bits (?) of bidirectional IOs, which could be enough for simple robotics and/or model train control...

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So overall, most of the MO5's extensions are easy to modify and repurpose. It's not only a great platform to learn about programming, but also to learn about hacking :-)