Here are the results of my initial TEST bit investigations. Setting TEST seems to cause a 1 cycle delay in which the processor is halted and the VIC makes some sort of non-standard access. It also seems to alter the contents of the VIC's 1 line video matrix and colour nybble at the location of the delay, though I haven't worked out where the new data comes from yet. It is not always $FFF; sometimes $000. I suspect this may come from main memory, since that contains 00s and FFs all over the place after powerup. After that, video and processor accesses continue as normal. Thus, to remove one character line from the display there must be 7 cycles between TEST being set and TEST being reset, not 8. It also seems to be possible to initiate a badline using TEST (presumably due to the incremented vertical line counter), though only during the first (halted) cycle after TEST was set. During the period where TEST is high and the processor is running, no badline DMA transfers are initiated even though the lowest 3 bits of RASTER can equal YSCROLL in this time. Nicolas, does this agree with your investigations? Richard -- Richard Atkinson Software Engineer Tenison Technology EDA Ltd http://www.tenisontech.com/ - This message was sent through the cbm-hackers mailing list. To unsubscribe: echo unsubscribe | mail firstname.lastname@example.org.
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