A system includes a plurality of devices that are connected in series and a controller that communicates with the devices. Each of the devices has a plurality of input ports and corresponding output ports. The outputs of one device and the inputs of a next device are interconnected. The controller is coupled to the first device and the last device of the series-connection. The controller applies a test pattern to the plurality of input ports at the first device connected in series, by the controller. Each data channel defines a data path between corresponding pairs of input and output ports of the first and last devices. A data channel is enabled if the test pattern is detected at its corresponding output port.