On CPC, the HSYNC and VSYNC signals are received from the [[CRTC]]. These signals are then modified and merged by the Gate Array into a single CSYNC signal that will be sent to the display.
When CRTC HSYNC is active, the Gate Array immediately outputs the palette colour black. If the HSYNC is set to 14 characters then black will be output for 14µs. The If a video mode change is pending, the HSYNC pulse width needs to be at least 2µs for Gate Array to change the video mode.
The HSYNC is modified before being sent to the monitor. It happens 2µs after the HSYNC from the CRTC and stay a maximum of 4µs (signal is cut short if HSYNC width is greater than 6).