> > This last part is very stupid. Of course it switches VIC banks, as the > > two bitmaps are in two separate banks. What I meant is that the bitmaps > > are in banks 1 and 2, and I see no way for $DD00 to accidentally point > > to bank 0 or 3 for a single frame. My thinking is that the garbage might > > be $3FFF or some such. > > How wide is the garbage? Only 8 pixels? If yes, then it could be that > the $DD00 output lines on the CIA do not change exactly simultaneously > (1->2 could become 1->3->2 or 1->0->2), or they change while the video > chip is reading the data, changing the A14 and A15 during an "address > valid" phase. I haven't experimented with this; I've always switched > video banks somewhere in the screen border. I should have explained in more detail. The interrupt, which does the $DD00 switching, is in the lower border (line 250 or so). It switches between bitmaps in banks 1 and 2 to get the interlaced pic. Most of the time, the picture would display fine. But at random intervals, an entire screen of garbage would appear, for just one frame -- the entire screen is full of garbage for that one frame, though. Also, the interrupt had a habit of "splitting", that is, occur a few lines lower on the screen. How can you get a raster interrupt to occur on different lines? Anyways, I should obviously get ahold of the code and send it over. But out of respect to your (and my!) studies, perhaps I will wait until January :). -Steve - This message was sent through the cbm-hackers mailing list. To unsubscribe: echo unsubscribe | mail cbm-hackers-request@dot.tcm.hut.fi.
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