A method of operating a system (1) having a first controller (2) to which a second controller (3) is connected, wherein the first controller (2) is connected via a data link (4) to the second controller (2) and exchanges data therebetween, and the first controller (2) is connected to the second controller (3) via a power link (5) and supplies the second controller (3) with power from a power source (7), characterized in that a sensor (8) of the first controller (2) is used to measure the current flow via the power link, and that the current flow is influenced by means of a load (13) of the second controller (3) for the purpose of data transmission between the two controllers (2 and 3) via the power link (5).