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CRTC

No change in size, 16 November
/* Rupture For Dummies (R5 bug) */
CRTC 1 has a bug that occurs when R5 is updated with a non-zero value when HCC=R0 and VLC≠R9, but only when R5 was previously 0. This changes the MA update source to R12/R13 instead of MA'. The CRTC then loads R12/R13 into MA at the beginning of every scanline, regardless of the VCC value.
The RFD This R5 bug also messes with the frame parity management. However, it is possible to fix the parity of the frame by activating/deactivating the IVM interlace mode.
The vertical adjustment operates normally after the RFD is triggered. If vertical adjustment is not needed, R5 can be reset at any time after the RFD is activated.
Phi2x
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