NMRA S-9.1 DCC Standards Jump to the NMRA Home Page or go up one page. Through the Rails Communication from a Digital Command Station to a Digital Decoder is accomplished by transmitting a series of bits that convey instructions. This portion of the standard covers the electrical characteristics of the digital command control signal that encodes these bits.
Alternate transitions separate one bit from the next.
The remaining transitions divide each bit into a first part and a last part. Digital Command Stations shall encode bits within this digital command control stream of transitions by varying the duration of the parts of the bits, or frequency of the transitions. Figure 1 provides an example of bits encoded using this technique. The NMRA digital signal applied to the track by any Digital Command Station shall have the following characteristics, as measured under conditions ranging from no load to the maximum continuous load permitted by the power source. This signal may contain ripple at the zero-crossing transitions, provided that this ripple shall have a frequency of no less than 100 KHz and an amplitude of no greater than one fifth the total amplitude of the NMRA digital signal.