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Any chance to take a look at such a font?

These markings are often confusing and mostly meaningless. If I had to guess, it looks like a Motorola-fabricated clock driver IC (MC74F803), similar to those used in Amiga, see this Wiki page. It seems to provide clocks for the CPU. You'll find the datasheet MC74F803 for on the above mentioned...

Please tell us the part number or post a picture...

Is there any place around here where I can dump all CUDA-related stuff (including pictures, schematics, firmware disassembly etc) I gathered so far? A kind of editable Wiki?

368 is the correct amount of required RAM. 386 was a typo. Sorry.

Sure. I attached three different binary dumps. Disassembly including my personal comments aren't included there. I need to take some precautions and don't post those here because they're surely copyrighted...

CUDA Firmware actually uses 386 bytes of RAM. It's divided into two main partitions as follows: $0090 - $00FF various local variables $0100 - $01FF 256 bytes of PRAM --> yes, PRAM is simply a part of the CUDA's internal RAM; since it's always powered (either by the mains or the battery)...

Well, damaged ADB circuitry is very unlikely then. This is good news indeed. Bad news: it looks like you're experiencing another hardware-related issue. Is it possible to boot up the machine with PRAM battery removed?

Last question: what happens with a keyboard attached? Does it respond when you press the TAB key/ any other key?

Hmm, if the Keyboard works as expected (different keys recognized) then it's safe to assume that the ADB circuitry is intact. I'd look for software-related issues. Does the mouse pointer respond to mouse movements during boot or is it frozen?

With a PIC/AVR, is it possible to assign a custom functionality to arbitrary pins?

Some more to check: is the failing mice attached directly to computer's ADB port? did you try to attach the Keyboard instead? Does it work then? tried with only one device at a time? I know these are very basic steps I assume you already tried out. Please double-check them anyway...

Could you shoot a picture showing the whole ADB circuitry (the connector and the 342S0440-B ASIC)?

Those are resettable SMD125 fuses similar to this one. The theory on their operation is well explained in this Wikipedia article. The fuse ABOVE the 342S0440-B ASIC is probably not the right one. It should be a fuse sitting between the ADB connector and the ASIC. Moreover, you should see a...

I would highly recommend the Badcaps Powersupply Troubleshooting Forum. There are some high qualified techs around there helping to identify old and obscure components and giving precious advises on replacement parts. They have helped me to revive my Astec PSU (from PowerMac 6100), see this thread.

No, it's a kind of misleading information spread across the Internet. PowerMac 6100 can address max. 264 MB, i.e. 8 MB soldered onboard memory + 2 SIMMs x 128 MB. See this post and this post.

Yep, already done + understanding and commenting it  :) That's a good idea indeed. The biggest problem could be CUDA's clocking. Although it's clocked by an external 32768 Hz crystal, it has a built-in phase-locked loop synthesizer (PLL) that is capable of rising the MCU internal clock up to...

68HC05E1

Yes. IIRC, three different CUDA firmware dumps are currently accessible: 341S0060, 341S0417 (CUDA v2.35 from Color Classic) and 341S0788 (CUDA v2.37 used in Quadras AV and PowerMacs). EgretManager has a call called read 6805 address allowing the programmer to read values from an arbitrary MCU...

Because Q700 doesn't have CUDA, it uses the "Bit-bang" ASIC instead, Apple part number either 342S0440 or 342-0440-A or 342S0440-B, see Mac Technical Notes.