From: Richard Atkinson (rga24_at_cantab.net)
Date: 2002-04-07 19:01:53
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. Richard Message was sent through the cbm-hackers mailing list
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