A method includes a controller detecting a signal state of a presence terminal that is associated with a bus device. The signal state is set by the bus device to indicate presence of the bus device in a connector, and the connector is connected to a bus. The method includes the controller communicating data over the bus; and in response to detecting the signal state, the controller communicating side channel data to the bus device to authenticate the data that is communicated over the bus as being provided by the controller. Communicating the side channel data with the bus device includes providing a signal to the presence terminal, which represents the side channel data.