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Q: The standard implies that the track voltage can range from 7 to 20 volts. Is this how speed and direction are controlled?

During operation, the voltage provided by the command station does not vary.

The DCC multifunction decoder within the locomotive controls speed and direction by varying the amount of power provided to the motor. The voltage of the DCC signal described in the standard is to allow for the different power needs of the various scales. For example, a typical Z scale command station will supply 10 volts, a typical HO scale command station supplies 14 volts and a G scale command station will put 20 volts on the rails.

The NMRA DCC Standard allows for a range of voltages on the track, as well as minimum and maximum voltages that a multifunction decoder must tolerate.

If you were controlling live steam locomotives, you would probably use the minimum 7 volt signal.

Edit FAQ Related Articles: Pulse Width Modulation, NMRA, NMRA/NMRA Standards, DCC Power Categories: Beginner, Command Station, Decoder

Q: Does retransmitting DCC packets consume all the bandwidth and affect throttles?

Although simple low end DCC command stations may provide for control of a limited number of engines and repeatedly cycle through all the addresses in use, higher end systems may use a priority-based scheme, where packets containing values which have changed are prioritised over those that have no changes. Thus, repeating packets does not necessarily impact the effective bandwidth of the system.

Edit FAQ Related Articles: Digital Packet Categories: Beginner, Command Station

Q: What is a decoder?

Main article: Decoder

A decoder is a device which listens to Digital Packets addressed to it, and then performs whatever action is requested. There are three types - multifunction, Function and Accessory Decoders. Some multifunction decoders are very simple devices providing only motor control and/or a small selection of lighting options, while others are very complex with multiple special effects, tuning motor response, and sound effects available. Function decoders are similar, except they lack the motor control functions. Accessory decoders are used for turnouts, signals and other animated items. Please see the decoder page for full details.

Edit FAQ  Categories: Beginner, Decoder

Q: Can you control things other than locomotive speed and direction?

Yes. The baseline packet in the standard only provides for basic locomotive control since that is all that is essential for interoperation. The extended packet format RP defines packets that can be used to control 32,000 different accessories such as lights, sound, turnouts, etc.

Edit FAQ  Categories: Beginner, Decoder

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