CRTC 1 has a bug that occurs when R5 is updated with a non-zero value when HCC=R0, but only when R5 was previously 0 at the end of the last character line. This disrupts the normal MA reload process, causing the CRTC to load R12/R13 into MA at the beginning of every scanline, regardless of the VCC value.
But if R5 is set back to 0 before HCC reaches R0 on the last scanline end of the current character line (when HCC=R0 and VLC=R9), the bug won't trigger.
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