=== VCC (C4) overflow ===
On all CRTCs, if Vertical Total (R4) is changed with a value less than VCC, then:
* if this update was done when VCC < R4, then VCC overflows and will continue to count up to its maximum value (127) before looping back
* if this update was done when VCC = R4, the current character line was already decided to be the last one of the current frame. No update to R4 will make the CRTC change its mind for the current frame
The only exception when VCC = R4 is for CRTC 1 with a value of 0, which will cause the VCC to overflow.
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=== HCC (C0) overflow ===
If Horizontal Total (R0) is changed with a value less than the current HCC, then:
* on CRTCs 0/1/2, HCC overflows and will count up to its maximum value (255) before looping back
* on CRTCs 3/4, the current line is considered finished and HCC is immediately reset to 0 on the next line
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