From: Marko Mäkelä (marko.makela_at_hut.fi)
Date: 2002-04-07 17:44:37
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?
Marko
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