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F18a or composite video


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F18a is great for playing games, but some times when beta testing its nice to have original VDP when developer wants to try game on "stock" hardware. I was thinking of using a FET switch to switch between F18a and TMS9928A. It would have a video amp (LM318) for composite video as well. Any interest in a mod like this?


Mod would use a slider switch to select between F18a and composite.





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I've thought a bit about this, though I've not done any experimentation yet. But so far as writes to the chip, they should be able to operate in parallel. It's only when you need to read information back that it becomes an issue.


So it MIGHT be enough to simply gate the read/write line so that only one chip or the other ever sees reads. True, the disabled chip may end up in some strange states, but you aren't looking at it and it shouldn't be able to impact the rest of the system anyway. It will definitely malfunction since it will see read cycles as writes (meaning you can't really run them in parallel even for compatible software, at least not with a hack as simple as I propose.)


Anyway, that's as far as that train of thought has gotten so far. ;)

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