A9 is a hotel guestroom control unit(RCU)which is the brain of the whole system.
It can be extended by the circuit I/O module.
It has:
   - 3channel RS-485 interface, one for modular expansion, another two for peripheral extensions.
   - LED screen for reset, test, error, and mode.
   - Standard rail mount
   - With a from-machine extension interface, resources can be expanded indefinitely