Editing Digital Command Control (section)

==Communication protocol==
[[File:DCCsig.png|thumb|right|A sequence of 7 bits encoded with DCC. Note the peak-to-peak voltage is constant and thus does not carry information. Note the given values of time are for each half-cycle of a square wave.]]The electrical waveform sent to the decoders (typically along the model railway track) serves as both a digital signal and carrier of electric [[Power (physics)|power]]. The power carried is the [[Amplitude|peak-to-peak]] voltage multiplied by the current. The voltage is specified by the NMRA to be based on the [[Rail transport modelling scales|modelling scale]].<ref name=":0" /> The data is encoded via [[frequency modulation]] by varying the period of individual [[Square wave (waveform)|square waves]]. A [[binary numeral system|binary]] 1 is represented by a {{val|116|ul=μs}} nominal [[Period (physics)|period]] (duration), while a 0 is represented by a {{val|200|u=μs}} nominal period. These 0 and 1 bits form packets which contain a preamble, the recipient decoder's address, an instruction, and a [[checksum]]. As such, the digital signal is encoded entirely in time and is completely independent of the waveform voltage. As there is no long-term polarity in the waveform, direction of travel of a DCC vehicle is independent of the [[Instant|instantaneous]] polarity between the rails, as it would in conventional DC operation. There is no ground reference in the DCC signal, and as such, either rail may be used as a reference to the other. Additionally, this means that a square wave beginning with a [[Signal edge|rising edge]] is interpreted identically as a square wave beginning with a falling edge, because the digital information is carried within the period of the wave.