Digitrax Command Control Glossary of Frequently Used Terminology

Many of the terms listed below are also covered in the Digital Command Control: The Wave Of The Future Clinic.

The Digitrax Big Book of DCC also contains an extensive glossary of DCC and Digitrax terminology.

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z NUMBERS

-Numbers-

128 Speed Step Mode: the motor voltage/speed curve of the DCC loco from stop to full speed has 128 discrete speed steps. This means that you have 128 discrete speed steps at your disposal for excellent speed control, especially at very low speeds. 128 speed step operation will give a significant improvement in speed control over 14 or 28 step operation. 128 speed step operation is only offered in advanced and professional level DCC systems.

-A-

AC or Alternating Current: An expression used to describe an electrical wave form that cycles or alternates above and below 0 volts. In the U.S., household electricity is 60 cycle, alternating 60 times a second, 110-120 volts.

Acceleration: The rate at which the decoder increases from one speed step to the next in response to a new increase speed command. Use CV 03 to set this value for each decoder. This feature is used to simulate train weight and to cause your model to respond more prototypically when you increase the throttle.

Accessory decoder: See stationary decoder.

Address, Decoder: a number assigned by the user to a particular mobile or stationary decoder. The DCC system uses the decoder address to send commands to the appropriate loco or accessory.

Address Range: each system has a certain number of addresses that it can handle. Basic DCC systems usually handle between 6 and 16 addresses. Advanced systems usually handle between 99 & over 9000 addresses and Professional systems almost always go to 9000 or more addresses.

Adddress 00: the special address used by DCC systems to send speed and direction commands to operate locomotives that do not have decoders.

Advanced (EPF) Consisting Method: Storage of the consist information in each decoder. The locos can be added to and deleted from the consist in any orientation. This method requires that all locomotives in the consist be equipped with decoders that support this feature(EPF decoders). This method allows you to set up a consist that will be "transportable" from one DCC layout to another but you must be sure to always put the locos back on the track in the same order and orientation you programmed them for or you can get some unexpected results.

Advanced Mode (28 Speed Step Mode): the motor voltage/speed curve of the DCC loco from stop to full speed has 28 discrete speed steps. This means that speed control will be limited to 28 steps. 28 speed step mode gives fine speed control. Increasing to 128 speed step operation will give a significant improvement in speed control, especially at very slow speeds needed for prototypical switching operations. Advanced mode is offered in most command stations because there are many decoders on the market that are not capable of 128 step mode operation.

Aliased 4 Digit Addressing: Lets you run 2 digit address decoders with 4 digit addresses by selecting them from the system Alias Roster. This feature gives you the ability to operate all DCC equipped decoders with 4 digit addresses. This is a function of the command station, not of the decoders.

Alias roster: a list of aliased addresses and their associated decoder addresses stored in a command station.

All live turnout: a turnout where throwing the turnout does not change the rail polarity. Also called non-power routing turnouts.

Ampere, amp(s): the unit of measure for electrical current used or provided by an electronic device. The current draw of most HO can motors is between .5 and 1.5 amps. DCC boosters usually provide between 2.5 & 10 amps. This means that in HO scale you can run between 4 and 6 HO locomotives on a 5 amp booster.

Analog Loco: A locomotive operating on a DCC layout without a DCC decoder installed. Also called a Conventional Loco.

Analog Mode Conversion: When a DCC decoder does not see DCC packets on the layout it changes automatically to DC operation. Digitrax decoders support analog mode conversion but not all DCC systems do. Analog conversion can be disabled by programming CV29.

Architecture or system architecture: the particular method and/or arrangement of system hardware components used a given DCC system (or other computer based system) for communication within the system. Examples of system architecture in the DCC context are peer-to peer communication and polled communication.

Armature: the rotating frame that supports the field coils of a motor.

Aspect: a combination of lights or positions on a railroad signal which has a defined meaning. This meaning is the signal's indication.

AutoReversing: a feature of some DCC boosters which allows a train to enter and exit reversing sections automatically without the need for the operator to throw a switch to match track polarities on either side of the reversing section.

-B-

Back emf: the voltage generated by the rotation of the motor armature. EMF is short for electro-motive force. Measurements of back emf are used for speed stabilization.

Ballast Lamp: A high current, low voltage lamp used to protect against unwanted voltage transits. In normal model railroad applications a 12 volt automobile brake lamp wired in series is used. For use as a buffer between DC and DCC, the lamp is connected across one of the double gaps separating the two systems.

Bandwidth: describes the volume of information that can be sent over a communication link.

Basic Consisting Method: Program all the locomotives in a consist to the same address and run them off one throttle. In this case all the locos must be running in the same direction.

Bi-polar: a wave function that goes from positive to negative and back. The DCC signal is a bi-polar signal.

Booster: Boosters receive the DCC signal from the Command Station, amplify it & put it on the track as the power that runs the locos. You can have several boosters on a system, each driving its own track section. You can have both regular or auto reversing boosters depending on your needs. Also called Power Booster, Power Station

Browsing: to scan sequentially through locomotive or accessory decoder addresses and status.

Buffer Track: See Ballast Lamp

-C-

Cab: See Throttle

Carrier Sense Multiple Access with Collision Detection (CSMA/CD): a signal and message handling system used by computer networks like ethernet. LocoNet is a CSMA/CD system.

Cascaded route: the operation of one or more turnouts by a function cell when it sends a request for the command station to initiate the necessary action.

Closed: the position of a turnout that is set so that the routing is through the straight leg or set for the main line.

Command Station: Each system has one Command Station that generates the DCC packets that tell the decoders what to do & produces Rail Sync so that all the devices you attach to LocoNet work together. With the Digitrax System you have a choice of several command stations to allow you to tailor your system to meet your needs. In an effort to keep the price down, we have chosen to combine command station functionality with other system hardware components. The Challenger Command Station is included in every DB100 series booster. The DCS50 Command Station/Booster/Throttle is the all in one unit called the Zephyr Starter Set. The DB150 Command Station is used as the command station in the Super Empire Builder Starter Set. The DCS100 Command Station/Booster is the command station for the Super Chief Starter Set.

Common (Loco Status): a DCC locomotive that is not currently "in-use" by a throttle connected to LocoNet but is still being refreshed by the command station. A loco with a status of "common" is selectable by any throttle on LocoNet.

Common Rail Wiring: A wiring system in which one side of all the track power supplies are connected. The common rail concept simplified block wiring in conventional DC systems, but is not recommended for new layouts installing DCC wiring. (see Direct Home Wiring).

Commutator: the rotating contact on the motor's armature that transfers power from the motor brushes to the field coils.

Compatibility: the ability of equipment made by various DCC manufacturers to operate together on the same layout. The interoperability of equipment from various manufacturers gives consumers more choices at every price level. It also gives you the assurance that if brand X goes out of business that you will still be able to buy equipment from another company.

Configuration Register (CV29): this special CV controls several different characteristics including: 1. Whether the decoder uses standard 14 speed step mode or advanced 28/128 speed step mode 2. Whether or not the decoder will automatically convert to DC operation when no DCC signal is present 3. In the case of Digitrax FX decoders, the relative direction of locomotive travel 4. Whether the decoder uses loadable speed tables and 5. Whether the decoder uses the 2 digit short address or the 4 digit long address.

Configuration Variables (CV's): these are special storage locations or "pigeonholes" in your decoders. By programming various CV's, you can control each decoder's performance characteristics. CV's store information like the decoder's short address, long address, start voltage, mid-point voltage, loadable speed tables and many more. Once you have programmed these characteristics, the decoders "remember" them until you change them again. The NMRA’s “Standard and RPs” define the usage of many CVs, others are manufacturer defined.

Conformance Seal: the “certification” issued by the after a product has passed the tests established and administered by NMRA volunteers to "prove" that a particular product follows “exactly to the letter” the “Standards and RPs” set up by the NMRA that pertain to that product.

Consisting: the action of linking more than one power unit together to be controlled by a single address. Also called Multiple Unit Operation, MU'ing, Multiple Unit Lash Ups, etc. See Basic consisting, Universal consisting & Advanced consisting.

Constant Brightness Lighting: because you have constant track voltage when you use DCC, you also have locomotive lights that stay on just like the prototype, even when the loco is not moving (unless of course you use their function lead to turn them off).

Conventional Loco: A locomotive operating on a DCC layout without a DCC decoder installed. Also called an Analog Loco or a Standard Loco.

-D-

Daisy chain: a wiring plan in which each device may be connected through other devices to the controller.

DCC: Digital Command Control. On the most basic level, DCC encompasses systems and products that are interoperable with the basic DCC industry norms and practices (the NMRA Standards and RPs are part of this). In addition, DCC includes other related technologies that are designed to enhance and extend the basic capabilities of DCC.

DC or Direct Current: An expression used to describe an electrical wave form in which the voltage remains more or less at a value above or below 0 volts. The wave form used by most model railroad locomotives. Sometimes referred to as Analog.

Deceleration: The rate at which the decoder decreases from one speed step to the next in response to a new decrease speed command. Use CV04 to set up the deceleration value for each decoder. This feature is used to simulate train momentum so that, just like the prototype, your model won't stop immediately when the brakes are applied.

Decoders, Mobile: the electronic device installed in each locomotive that receives the signal from the command station through the track, decodes it & tells the loco what to do.

Decoders, Stationary (Accessory) : the electronic device for the switches or other accessories that receives the signal from the command station through the track, decodes it & tells the switch/accessory what to do.

Decoder Status: a DCC decoder can be New, In-Use, Common, or Idle in a Digitrax system.

Detection section: a section of track gapped on one or both rails and connected to an occupancy detector.

Direct Home Wiring: A wiring system in which the DCC booster powers each rail through an individual conductor or wire. Each booster is wired to it's own power section and there is no common connection between boosters. This is the Digitrax recommended wiring system.

Direct Programming: A type of service mode programming.

Directional Lighting: loco lights can be set up to automatically change so that the forward lamp is lit when the loco is moving forward and the reverse lamp is lit when moving in reverse.

Dispatching: use your DT Throttle to set up a loco or consist you want to be run by an operator on a Utility throttle (or BT2 Buddy throttle) and then using couple of keystrokes, dispatch the loco from the DT Throttle and acquire it on the Utility Throttle or BT2. This feature may also be used by operators who wish to use a fairly strict dispatch discipline in their operating sessions.

Display Active: With the DT Throttle you can control two different addresses at the same time, one on the Left Throttle and another on the Right Throttle. Because only one throttle’s date can be displayed on the LCD screen at a time, we use the direction indicator to indicate which side is currently "display active". The "display active" throttle is the one with the flashing indicator.

Ditch lights: prototype lights that are mounted on a loco's pilot or low on the hood to illuminate each side of the track just in front of the loco. When the horn is sounded, they flash alternately increasing the visibility of the loco, especially at grade crossings. Digitrax decoders with FX lighting simulate this effect beautifully by using two separate function leads.

Droop: the slope of the graph of speed vs. load for a loco. This variable is used to calculate speed corrections made when scaleable speed stabilization is used to manage the effects of load on the loco's speed.

-E-

EPF or Extended Packet Format: an extension of the baseline DCC format that allows us to use long addressing and other expanded decoder features.

Event driven: a strategy for using a network's communication resources that sends traffic only when devices attached to the network need to communicate. LocoNet is an event driven network as opposed to a polled system which requires that each device communicate with the master in turn.

Exact feedback: the method of using a number of switches or sensors to determine the exact position or state of a turnout or other device.

-F-

Fast Clock: used by many operators during operating sessions to simulate prototypical operations. Traditionally, this clock is on the wall and is set up to run at a faster than normal rate so that you can "get in a full day's work on the railroad in a fraction of the time."

Forward trim: a scaling factor applied to all speed step power values in a speed table for the forward direction of the loco.

Function cell: a group of electronic components within a stationary decoder that controls the logic for a pair of decoder inputs and outputs. Used to operate local routes.

Functions, Decoder: function leads are extra decoder wires that you can connect to any device on the loco that you want to control from the hand held or other input device such as a computer. These can be used for locomotive lighting, sound units, smoke units, and other locomotive animation tasks.

FX Functions: specially designed functions (available on Digitrax FX series decoders) that let you set up lights on your loco to simulate Mars lights, Gyra lights, ditch lights, rotating beacons, single or double pulse strobes, flashing lights, random firebox flicker and more. CV's 49-63 are used to set up these special light effects.

-H-

Hexadecimal: the base sixteen number system. The digits used are 0,1,2,3,4,5,6,7,8,9,A,B,C,D,E, & F. You will see some values expressed in hex on some Digitrax throttles because with this system you can express numbers above decimal 99 as two digits.

-I-

Idle (Loco Status): DCC locomotive that has been addressed by the system previously, is currently selectable by a throttle on LocoNet, and is not being refreshed.

In-Use (Loco Status): DCC locomotive that is currently under the control of a throttle connected to LocoNet. An in-use loco is having its data refreshed by the command station and is not selectable by other throttles on LocoNet. The exception to this is if a throttle "steals" an in-use loco.

Indexing: the process by which a turntable bridge is aligned with approach or stall tracks. This process can be automated by using DCC decoders.

Indication: the meaning given to a particular signal aspect.

Interoperability: one of the most important features available in a command control system. Interoperability means that you can use your DCC compatible equipment with other DCC compatible equipment made by different manufacturers.

-K-

Kick start: an entry in a speed table that regulates the burst of power sent to a motor when the decoder first commands it to start (at speed step 1).

-L-

LAN: Local Area Network.

LCD: Liquid crystal display. Digitrax throttles with displays use LCDs.

LED: Light emitting diode. Many locomotives use LEDs for headlamps and other loco lighting. They do not generate any heat but their lighting characteristics are not as "crisp" as incandescent bulbs.

Loadable Speed Table: use CV65 through CV95 to define each discrete speed step in a 28 speed step curve. This feature allows you to customize a loco's performance curve and makes speed matching of locomotives possible. With this feature you can limit the top speed of a loco. Once you have programmed CV65 through CV95 to set up the table, you will also need to set up CV29 to enable it. This allows you to enable and disable the table at will and to keep the table stored even when it is not in use. Digitrax FX & 4th generation decoders go one step further and give you 128 speed step resolution with loadable speed tables.

Local route: the operation of a number of function cells within a single stationary decoder independent from the command station.

LocoNet: Digitrax's powerful communications network especially designed for model railroad operation.

Long Address: 14 bit address, extended packet format address.

-M-

Manual block system: prototype train control system where by trains run from block station to block station. Trains require explicit authority to enter each block. Also used as the backstop method if an automated signaling system fails.

Master/slave: a system architecture where a central controller manages communications among attached devices. Master/slave usually uses polled communications.

Max voltage (Vmax): CV05 specifies the exact voltage to apply to the motor at speed step 28 in a 28 step system and step 14 in a 14 step system. Setting CV05 limits the top speed of the loco.

Mid-Point Voltage: CV 06 specifies the exact voltage to apply to the motor at speed step 15 in a 28 step system and step 7 in a 14 speed step system. This allows you to make a quick adjustment to the motor voltage/speed curve without setting up a loadable speed table.

Momentum: expresses an object's tendency to keep moving at its current speed and direction.

Motorola trinary format: a digital command control format used by Marklin AC digital HO and Marklin Maxi decoders. This format is the largest format used in Germany and is not compatible with DCC. Some command stations like Digitrax DCS100 and Uhlenbrock can output both Marklin Motorola and DCC formats simultaneously.

MU: Multiple unit operations. See Consisting.

-N-ze:12.0pt'>

Nested consist: a consist that is part of another consist. Digitrax systems can handle nested consisting.

Nested route: a route that is part of another route. Digitrax systems can handle nested routes.

New (Loco Status): DCC locomotive that has not been addressed by the system. A new loco is selectable by throttles on LocoNet and is not refreshed.

Non-power routing turnout: a turnout where throwing the turnout does not change the rail polarity. Also called all live turnouts.

Non-retriggerable: a stationary decoder function cell is non-retriggerable if it must complete its current output action before accepting a new input.

Normal direction of travel: the direction a decoder recognizes as the forward direction when the throttle is set for forward motion. Some decoders can be set up so that either long hood forward or short hood forward is the normal direction of travel depending on what the prototype practice was for that particular locomotive.

NMRA: National Model Railroad Association. An organization of hobbyists based in the United States.

Ntrak: the most widely used Standard for N scale modular layouts.

-O-

Occupancy detector: a device that senses the presence of rolling stock on a section of track and provides feedback to the system.

Ohm(s): the unit of measure of electrical resistance.

Operating current: the current draw, stated in amps, used by a loco, including its motor, lights and other accessories when operating continuously under normal continuous at full load. This measurement is important for determining which decoder to install in the loco.

Operating Mode: 14 or 28/128 speed steps. See also, Speed Steps, Standard Mode, Advanced Mode & 128 Speed Step Mode.

Operations (OPS) Mode Programming: lets you program CV's in DCC locos equipped with EPF decoders while they are on the mainline. A typical use for ops mode programming would be to change the acceleration rate (CV03) or the deceleration rate (CV04) of your locos to simulate the weight and braking characteristics of the train to compensate for changing the number of cars and power units in the train.

-P-

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 den 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.

-R-

Recommended Practices (RPs): are set up by the NMRA an adjunct to the Standards. RPs are not mandatory but if a feature covered by an RP is implemented, it should follow the RP.

Receiver: an electronic device that performs a similar function to a DCC decoder in a carrier control system. DCC decoders do more than just receive information, they actually decode it, determine if it applies to them and then control the loco based on the decoding.

Refreshed (Data): DCC command stations re-send data to decoders many times to be sure that the signal is not lost and that you have reliable operation. All in-use and common locos in the system will continue to be refreshed until they become idle.

Retriggerable: stationary decoder configuration that allows the decoder to accept new input and begin a new action before completing the current action in progress.

Reverse trim: a scaling factor applied to all speed step values n a speed table for a loco moving in the reverse direction.

Reverse loop or reversing section: any track layout that allows a loco to enter and exit on the same rails while moving in the same direction. This creates a track polarity mismatch at one end or the other of the track section which must be corrected in order for the loco to continue moving.

RJ12: standard type of telephone style plug and socket used for six conductor cable.

Roster: The Alias Roster is a database of 4 digit numbers that are matched to 2 digit decoder addresses. This Alias roster defines all the power units you wish to operate this way, & is stored in the DCS100. The DCS100 remembers the Alias Roster even if the system is powered down between sessions.

Route: a group of turnouts and their specified positions that will be triggered by the activation of a single "TOP" switch address to a specified position.

Rule 17 dimming: requires locos waiting to be passed and in other circumstances to dim their headlights. Digitrax FX decoders allow you to use rule 17 dimming.

-S-

Security element: the plant including track, associated with any reporting, interlocking and/or signaling for that track. Also called simply "plant."

Selectable: a DCC decoder is selectable when it is not currently in-use on another throttle.

Service Mode Programming: service mode programming information sent by the command station or programmer as a broadcast signal that goes out to all decoders on the track. Some command stations have separate packet generators to provide independent service mode programming outputs so that the layout can continue operating while decoders are programmed. Others require that the layout be shut down and the packet generator be used for programming decoders.

Short Address: 7 bit address, baseline packet format address

Slot: a memory location in the command station that holds an active decoder address.

Slot Following: when more than one DT Throttle is logged on to a single loco address, both DT Throttles will be controlling that address and both DT Throttle displays will be updated with the same information. In other words, both operators will see what the other is doing.

Speed Stabilization: the use of back EMF by a decoder to modify power to the motor to keep speed constant. Speed stailisation can also be scaled to make the feature more useful. It's like "cruise control for your loco."

Speed Steps: because DCC is a digital system, locomotive speeds are defined by discrete speed steps. DCC systems typically offer 14, 28 or 128 speed steps. This means that as motor voltage is increased that the speed of the locomotive increases in a straight line from stop to full speed with discrete speed values at each voltage.

Split Field Motor: Another term for AC motor.

Stall Current: the max current draw in amps for a motor when it is stalled. This is important in determining which decoder to install in a locomotive.

Standards: “ Standards” cover many aspects of interchange for model railroading. The DCC “Standards” are only a small part of the NMRA’s “Standards Program”. The DCC standards are a small part of the industry norms and practices that make up what we know as DCC.

Standard Mode (14 Speed Step Mode): the motor voltage/speed curve of the DCC loco from stop to full speed has 14 discrete speed steps. This means that speed control will be limited to just 14 steps. 14 speed step mode gives reasonably good speed control. Increasing to 28 speed step operation will give much better speed control and going to 128 speed step operation will give really excellent speed control. Standard mode is offered in most command stations because there are many decoders on the market that are not capable of 28 or 128 step mode.

Start Voltage: or V-Start is the voltage added to the motor drive voltage at the first speed step. This adjustment allows you to trim the loco to compensate for its motor efficiency.

Status Editing Decoders: a DCC decoder's status can be manually changed by a Digitrax command station at any time the decoder is selectable.

Stealing a Loco: this procedure allows a DT Throttle user to override the in-use interlock and force the throttle to log on to an in-use loco. This can result in having two throttles logged on to and controlling one address. See also Slot Following.

-T-

Throttles: Throttles are input devices that tell the Command Station what you want the decoders to do. You can have many throttles on your system. The number is determined by the capabilities of the Command Station you are using. You can also use a computer to create "soft" throttles. Sometimes DCC throttles are also called "Cabs."

Thrown: the position of a turnout where the routing is through the curved leg or set for the diverging route.

TOP Locomotive: We call the "key" locomotive that other locomotives are consisted TO, the TOP locomotive because it does not need to be in any particular physical order in the consist. The TOP locomotive address controls the speed & direction of all locomotives consisted to it by the MU function. The "TOP" locomotive does not have to exist. You can use a 2 digit train number, for example , as your "TOP" locomotive.

Track feed: a short section of wire that connects the power bus to the track and supplies track power.

Transponder or Transponding Device: A device used in a locomotive, car or caboose that sends identification and position information about the unit to the LocoNet system via transponder detectors. Digitrax transponding devices are not unique to DCC and can be used on many other power formats.

Transponder Detector: A device used to receive information from transponding devices on the layout and transmit that information to the LocoNet system. Digitrax transponder detectors are not unique to DCC and can be used on may other power formats.

Trigger: an event that causes an action to occur.

Trinary format: See Motorola Trinary Format.

-U-

Universal Consisting method is handled by the command station and allows you to consist locos with any DCC decoder as well as an analog loco. The locos can be added to and deleted from the consist in any orientation head to head or tail to tail.

-W-

Whole layout common rail: layout wiring method where power districts and their boosters are connected electrically by a common rail or common power bus return wire.

-Z-

Zero-Stretching incorporates a time period between packets to give you an effective DC offset between the two rails. This allows you to control a DC locomotive along with the DCC locomotives on a DCC system.