In my simulator lets say Radio Sub System. I have a radio head (which i used to call them slaves) connected to an Arduino with a CAN module.
in one scenario, the master can send messages to the LRU(radio) to turn on lights, and other things.
in the second scenario, the LRU(slave) can send a message to the host. ie the pilot changes the frequency.
I am currently building an ethernet to CANaerospce bridge on a EK-TMC4129xl Tiva C launchpad.