I am designing a UI PCB which has an MCU which will interface with a main system controller (MSC) on a separate PCB. The UI PCB provides an initial power up to the MSC which then boots up its onboard PSU and everything else. Additionally it should read messages from the main system controller to provide on the UI (LED's, display etc.). Finally it has buttons to power on, or reset the main system controller.
The UI PCB communicates with the MSC using CAN bus. I was just wondering if I would need additional IO's between the two PCBs? Can I send the data from the buttons on the UI board (like if it was being used as a state machine) as a message on CAN bus? Or would using a simple GPIO make more sense for this?