Abstract: A plurality of controlled devices are connected to a controller in such a manner that the first device is connected by a cable to the controller, the second device is connected by a cable to the first device and so on. Interconnection means at each controlled device, which connects the cable from the previous device to the cable connected to the next device, automatically assigns a unit address to each device depending upon the position of that device in the chain of devices. Thus, if four devices are connected in a chain to the controller, their addresses are 1, 2, 3 and 4, beginning with the first unit connected to the controller and ending with the last unit in the chain of devices.