Regardless of whether they’re generated by DELTA Control, Control Unit, Digital Railrunner, EEDTS Pro or something else, digital locomotive control signals in the ‘Motorola format’ all look pretty much alike on the rails. If you want to view these signals live on a PC monitor, you need the data monitor described in this article.The Märklin digital control protocol has already been described a good number of times (for instance, in the May 1999 issue of Elektor Electronics). We can thus limit our description of the theory to the bare essentials. The data are transmitted in the form of pulse packets consisting of 18 individual pulses or 9 pulse pairs. The voltage levels on the rails that are used to transmit the pulses are approximately –15 V and +15 V, with the exact values varying according to the control unit used and the degree to which it is loaded by the connected devices.