From: Jozsef Laszlo (laszloj_at_psi.com)
Date: 2002-05-02 11:19:26
>
> Dual Port RAM is a good way of solving the problem, yet quite expensive
> though. You'd need to re-engineer your whole C-64 board. Hm... *thinking*
> How about disabling the output enable of the internal DRAMs and putting this
> DPRAM on an expansion board, so the VIC can read its data through the
> expansion port? (I think the demultiplexed address is available as well, in
> order to be able to access the CHAR ROM.) I would have to dive into the C-64
> schematics to see how far we can get. If anyone will do this, I am surely
> interested in the solution.
Well... I think we need to remove the original DRAMs and then put the dual port
ram.... it means we need to hack the C64 main board.
I know it's not easy but once I have seen a schematic about 2Mhz C64,
there was a solution for access the static rams...as far as I remember there was
2 HC574 or HC374 buffers for the address lines and some TTL logic. Not too
complex.
> What the busy is concerned, true DPRAMs will only assert BUSY if the same
> location is written from both ports, which will never be the case if the VIC
> chip is on one side (since it never writes).
I'm not 100% sure in it... isn't the busy line activated when the same cell is
read
by both port? It's not clear in the documentation at all.... but if you're right
this
is the best case!
All in all... I belive in this dual-port solution...
regards,
Jozsef
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