Re: Commodore datassette for the Oric-1

From: Richard Atkinson (
Date: 2002-04-07 19:01:53

  • Next message: Nicolas Welte: "Re: Commodore datassette for the Oric-1"
    On Sun, 7 Apr 2002, Marko Mäkelä wrote:
    > Yep, the video chip definitely makes the Oric the Spectrum of the 6502
    > world.  Without hardware modification, it's almost impossible to write a
    > raster interrupt routine.  (I say almost, since one probably could
    > observe the memory access patterns of the video chip by reading from
    > unconnected address space (if the Oric has anything like that).)
    The "hardware modification" you speak of can be done entirely externally -
    it's just a lead going between the monitor connector (and SYNC pin
    thereof) to the cassette connector (IIRC). And the VIA's own timers can
    then be used once synchronisation is achieved.
    >  > It uses a MOS 6522 VIA to control the PSG data, address and control
    >  > busses with some very interesting hacks resulting from this method
    >  > of controlling the PSG.
    > Could the slightly audible distortions from the internal speaker while
    > trying to load from tape be caused by this?
    I haven't got a reference handy of which lines (if any) the cassette
    shares with the PSG, but it sounds like simple power supply noise issues
    to me.
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