The only exception is for CRTC 1 with a value of 0, which cancels the current HSYNC.
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=== 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 VCC to overflow.
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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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=== 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 VCC to overflow.
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