Connect a new accesory to the base robot

[dgiral57]

I am trying to connect a new accesory to the robot over the half-duplex RS-485 bus located on the right corner of the base. (My robot only has one connection plate, the one with an ethernet port and the bus).

i can already energize the board, switching the breaker. I cannot send any command though. I guess I need to get access to the mainboard in order to send messages to the mcb of the accesory. how can I communicate with the mainboard to send messages to the mcb?