Re: Commodore datassette for the Oric-1

From: Marko Mäkelä (
Date: 2002-04-07 17:44:37

  • Next message: Richard Atkinson: "Re: Commodore datassette for the Oric-1"
    Richard Atkinson wrote:
     > Although the Oric video chip is quite interesting in itself
    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 funny thing about the video chip is that it has no memory-mapped
    registers.  It is entirely controlled by the contents of the video
    memory.  Some sort of a "textual frame buffer" device, or similar to
    Ceefax or Teletext chips.  This is a good thing for hardware hackers, 
    since the video chip will always come up with a picture, even if the 
    processor does not work.
     > 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?
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