The VSYNC is used to sync the display of each frame for the devices in a cascaded chain. this command is a write-only command. The devices receive VSYNC command one time from the controller in each frame, and the VSYNC command needs to be active for all devices at the same time.

Because some devices receive the command earlier in the data chain, they need to wait until the last device receives the command, then all the devices are active at that time. To realize such function, each device needs to know its delay time from receiving VSYNC command to enabling VSYNC. The device uses some register bits to restore the device number in a data chain. This number minuses the device identification, and the result is the delay time of the device.

Because the sync function has been done by the device, the controller only must send the VSYNC command to the first device in a data chain.

Figure 8-19 VSYNC Write Command