DCC Digital Command Control
History: The first application of remote control for model railroading was developed by Lenz Elektronik GmbH in the 1980s for two German model railway manufacturers, Märklin and Arnold. Beginning in 1992 NMRA developed a standard for digital control based on the Lenz system which was later named Digital Command Control. The first commercial systems based on the NMRA DCC standard were demonstrated at the 1993 NMRA Convention.
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NMRA Communication Standard
The DCC standard is defined by two NMRA documents:
S-9.1 Electrical and S-9.2 Communication. These standards define how commands are sent to model locomotives using track power supply. By analogy with previous introduction to radio control, track DC voltage is the carrier of DCC message protocol which is the modulating signal created by alternating track voltage polarity. 
Based on user input, a DCC message is created as a logic-level signal with levels roughly zero and +3 volts.
The DCC logic-level signal is amplified to voltage and power levels capable of operating model trains by a Command Station which is an expensive piece of equipment.
Thinking ahead to radio, the duration of a "1" bit is 2 x 58 = 116 uSec. If the signal is all "1"s, it's frequency is 8.62 KHz. which is easily within capability of 900 MHz ASM band.
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User Interface
The earliest DCC user interface was a hand-held controller (throttle) connected to the Command Station by a cable.
A wireless throttle produced by CVP Products in 1999 was the first radio application for DCC. It was a popular and innovative product at the time, winning Model Railroader Magazine's most innovative product award. It replaced the throttle cable with a radio connection between throttle Command Station. However, locomotives continued to be controlled by original DCC through the track. Decoder
DCC from the rails is rectified for loco power and DCC signal (logic-level) is connected to a microprocessor for loco operation. Motor speed and direction is controlled using pulse-width modulation (PWM), outputs for other devices include voltages for lights and audio for speakers.
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