On CRTCs 0/1/2, the sole condition to trigger a VSYNC is that VCC=R7. While on CRTCs 3/4, it is necessary to have VCC=R7 and HCC=0 and VLC=0 to trigger a VSYNC.
On all CRTCsAlso, a new VSYNC cannot be triggered if VSC!=0. So we cannot trigger a new VSYNC during a VSYNC. The same goes for on CRTCs 3/4 HSYNCoccurs 1µs later than on CRTCs 0/1/2.
On all CRTCs 3/4, a new VSYNC cannot be triggered if VSC!=0. So we cannot trigger a new VSYNC during a VSYNC. The same goes for HSYNC occurs 1µs later than on CRTCs 0/1/2.
The HSYNC and VSYNC signals from the CRTC are not directly connected to the display. They are passed to the [[Gate Array]] for further modification. See its wiki page.