RE: 6510 CPU extensions - RAMs

From: Gideon Zweijtzer (
Date: 2002-05-02 10:58:23

  • Next message: Jozsef Laszlo: "Re: 6510 CPU extensions - RAMs"
    |Sorry guys, probably I missed the beginning of this discussion but there is
    |an idea... what about multiport static rams? These rams has two separated
    |address/data/control port so it's possible to access them with two devices.
    |One is the VIC chip (here of course we need to "convert" the DRAM address
    |lines into normal static address.. but it's possible), and the other device
    |CPU/system. Have a look at it:
    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.
    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).
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