6128 - internal RAM upgrade to 320/576/1088KB?

[eto]

I know it's not recommended as we have cheap solutions to add memory externally, but just for curiosity:

Would it be possible to e.g. replace the second bank of the 6128 by 41256 chips and drive the A8 line of these chips with a bit of additional logic? At least when someone has to replace his internal memory anyway, it might be a nice gimmick to add more internal RAM with a bit of more effort. 

My idea was, to remember D3 and D4 when the PAL is addresses in a flip flop and then combine those with CAS1 and ROW to drive the A8 signal. See picture attached. Would that idea work?

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If yes, the Yarek 1-4MB solution probably could also work, by adding a bit more NOR logic and using a SIMM (ok, definitely ugly inside the CPC). 

If the idea is not possible, I'm happy to learn. It's just an idea and I wonder if I am totally wrong with it, or if I missed something.  

[GUNHED]

See German ct magazine, they did a 512 KB internal expansion for the CPC6128. 256 KB can be accessed by CRTC!

[eto]

See German ct magazine, they did a 512 KB internal expansion for the CPC6128. 256 KB can be accessed by CRTC!

I know that one. But they replaced the PAL and the whole solution is not (fully) DK'tronics compatible. What I had in mind was to get something that is 100% compatible and behaves exactly like an external RAM extension with up to 4MB. 

[GUNHED]

Yes, that would be the greatest solution. And there are already two solutions there. One is internal, works fine. the other one is the 4 MB expansion card. Works fine too. Thereads about that are somewhere in this forum.

Good luck with your solution, hope you stay compatible to the CPC6128 (dk'tronics is just a subset of it).