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18 Glossary Terms starting with p

Word Description
Packet The organization of bits and bytes into complete DCC commands. A DCC packet consists of a preamble, address, instruction, and error detection information with bits to indicate the start and end of the packet.
Paged Programming A widely used type of service mode programming.
Peer-to-Peer A network communications protocol where messages between devices are not managed by a central mediator. LocoNet is an event driven peer to peer network.
Physical Register Programming A primitive type of service mode programming.
Polarity The two directions of current flow, plus (+) and minus (-), in any electrical circuit. Mismatches in track polarity create reversing problems.
Polled Communications The process by which devices attached to a system are interrogated sequentially by the master to see if they have information or commands to transmit to the system.
Positive feedback The method of using a switch or sensor to determine one of the two possible positions of a turnout or states of a device.
Power Booster See Booster.
Power Bus The main wires that carry power from the booster to provide power feeds to the power district. The power bus is very important for DCC layouts since the DCC signal is carried on the power to the layout. If there is not good power everywhere on the layout, then the locos will not "see" the DCC signal.
Power District The power wiring, components and equipment attached to that wiring, driven by a single properly isolated booster.
Power Routing Turnout A turnout where only the route selected is live and the rail polarity changes when the turnout is thrown.
Power Station See Booster.
Power Sub-District A subdivision of a power district. Usually controlled by a power management device like a PM42.
Power Supply A transformer that provides power to the DCC system. The transformer is not usually included with the DCC system.
Programming The action of entering data into DCC decoders.
Programming Track An electrically isolated track section used for decoder programming. This track ensures that broadcast programming instructions are only sent to the decoders you want to program.
Purging The process by which Digitrax command stations automatically release DCC locomotives from "in-use" to "common" when they are not under the control of a throttle connected to LocoNet for approximately 200 seconds. This makes locos that have been "forgotten" by their operators available to be selected by other operators to prevent collisions during an operating session. In the DCS100 purge time can be lengthened to 600 seconds or disabled completely.
PWM Pulse Width Modulation. Allows for control of power to a motor by varying the length of full power pulses sent to it. PWM is the "magic" that lets us operate an analog loco on a DCC layout.