If a graphics mode change is pending, the HSYNC pulse width needs to be at least 2µs for Gate Array to change the graphics mode.
The C-HSYNC is modified before being sent to the monitor. It happens begins 2µs after activation of the CRTC HSYNC and stay stays a maximum of 4µs (signal is cut short if HSYNC width is greater than 6).
For example, if CRTC R2=46, and CRTC HSYNC width is 14 chars then C-HSYNC starts at 48 and lasts only until 51 included.