CAL provides one input port (BYS_PI) and one output port (BYS_PO). Video timings and image sizes may be different on the input and output port. It is allowed that:
Data is sent to BYS_PO and data is received on BYS_PI.
Data is sent to BYS_PO but nothing is received on BYS_PI.
Nothing is sent to BYS_PO but data is received on BYS_PI.