On CRTC 1, at the beginning of every raster line of the first character line of the frame (ie. when VCC=0), MA is loaded with R12/R13 instead of MA'. '''This is a major source of incompatibility if the programmer does not take care.''' In demos and games, to be compatible with all CRTCs, program R12/R13 only when VCC != 0. This will then take effect at the next CRTC frame start.
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==== Rupture For Dummies (R5 bug) ====