The only exception when VCC = R4 is for CRTC 1 with a value of 0, which will cause 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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* on CRTCs 0/1/2, VTAC overflows and will continue to count up to its maximum value (31) before looping back
* on CRTCs 3/4, the current line is considered the last one of the current frame and vertical adjustment ends
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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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