Programming Track

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Short Definition


A programming track is used to program decoders. For mobile decoders, it's easiest to have a portion of your layout track to double as a programing track. Typically, it's best to have your programming track near your programming device (Command Station, SPROG, or Computer). For greater flexibility the track should be part of the layout trackage. The reason for this is to minimize handling of finely detailed locos on your layout and allows you to simply drive your loco to the programming section, and read/change values of the decoder.

Every layout should have a program track. It does not have to be on the layout, it could be a test track on the workbench. An engine service track or a turntable could also be used.

Reasons for the Program Track

The biggest reason to have a Program Track is to prevent damage to a decoder.

The programming output on the booster is current limited. Boosters that lack that output usually include a resistor that is installed in series with the track circuit to limit the current. The resistor is not needed for normal operations. The NMRA Standard S-9.2.3 defines the Service Mode/Program Track. It requires a separate, isolated track for programming which is both monitored and current limited. The decoder will acknowledge an instruction with an increased current draw of at least 60mA for 6ms, often by pulsing the motor.

Some decoders have built-in short circuit protection, others do not. An incorrectly wired decoder can be destroyed when exposed to the track voltages used on a DCC layout. Any new, untried decoder install should never be placed on the layout, but on the programming track. Should there be an error, the decoder will not be destroyed on the program track, due to the current limiting feature.

For sound decoders, a programming track booster can also be installed to feed the programming track. Not all systems require this, but many sound decoders cannot be programmed without one. See below for more info on programming track boosters.

The disadvantages of having a programming track:

  1. The dedicated programming output is usually only found on more sophisticated (read expensive) boosters.
  2. A dedicated programming track must be constructed, either on your layout or the workbench.
  3. The locomotive/decoder combination to be configured must be moved or placed on the programming track.
  4. Motor operation and functions cannot be used or verified on a programming track. That must be done on the layout or a DCC powered test track

Of course, there are advantages to having a program track.

  1. Progamming is done in a controlled manner, with low voltages and currents, eliminating the risk of damage possible when a miswired decoder be exposed to full DCC power on the mainline.
  2. Decoder address is not required to configure it. Also eliminates the possibility of programming all the motive power on the layout.
  3. CV values can be read and recorded manually or via software for easy record keeping
  4. A mistake made during decoder wiring will be forgiven. It won't cost you a decoder.

Refer to NMRA S-9.2.3 for more information.


The biggest problem people have with programming track is that if the a train enters the programming track, and the switch is set for programming, the power pickups of the locomotive will short the two segments together. To prevent this, you need to isolate the programming track from the running track so that in case a locomotive enters the programming track area when it is set to programming no harm is done.

With the solution provided below, the worst that will happen is that the train will stop running once the last power pickup enters the isolation area. (Some decoders may creep forward during programming as a method of acknowledging the command was accepted, which can be an issue when using a method like DecoderPro to write multiple CVs. Particularly on a sound decoder.)

Isolating the Programming Track

To prevent a locomotive being programmed from accidentally shorting the program track you need a section of track as shown below. The programming section needs to be at least 50% longer than your longest locomotive and the isolating section must be longer than your longest locomotive too. The longer the programming track is the more useful it will be.

Remember, some will creep forward during programming, so the longer the track the better. Modern decoders have an acknowledgement feature built in. A program such as DecoderPro will send a new CV value to the decoder. If it works, the decoder will acknowledge this by briefly energizing the motor. DecoderPro can by the same method read the CV values. It just sends every possible value sequentially until the motor is energized. Thus, when programming a large number of values, or reading them back, the locomotive can creep forward quite a distance. Keep that in mind when planning the length of your programming track


Wiring the Track

This is an example of how to connect a 4PDT (4 Pole, Double Throw) switch to the track. When the switch is in the normal position both sections of the track are connect to the layout and act as part of the layout. When the switch is the programming position, the program track (BROWN+BLACK wires) is connected to the program device and the Isolating section (RED wires) is totally disconnected and the LED turns on. The red LED can be a signal near the track, or mouinted between the track, or on the front of the facia, or both.

Why is a 4PDT Switch Used


Many modellers are of the opinion that two DPDT switches can be used. They are not incorrect.

Inevitably a mistake will occur or a switch will be changed accidentally, causing damage to your command station. A 4PDT prevents accidental misconfiguration of the program track by only offering two possible states. Using two DPDT switches offers 4 possibilities making misconfiguration very easy to accomplish.

A Note Regarding Switches

The best choice of a 4PDT switch for your program track is a Center-Off version. This ensures that one circuit is completely disconnected prior to the new connection being established.

Switches are available as "make before break" and "break before make". For this application, a "break before make" is essential, and a center-off version is the easiest way to make sure the switch breaks before making a connection. This avoids the possibility of momentary connecting the booster output to the programming track output terminals.

4pdt switch.JPG

Normal output to the track from the booster. In this mode, the program track and isolating section is connected directly to the booster output and function as normal trackage.
Command Station
Output from the Command Station's dedicated Programming Track outputs, if equipped. If your command station lacks these connections, consult the manual for the proper wiring of a program track, which may require a series resistor to limit the current in this mode.

The left half of the switch selects the power source that connects to the programming track (BROWN+BLACK wires). When the switch is in the Normal position, the programming track is connected to the layout, and acts as part of the layout. When the switch is in the Program position, the program track output from the command station is connected to the programming track.

The right half of the switch controls the isolating track (RED wires). In the Normal position, the isolating section is connected to the main line. In the Program position, the isolating section is totally disconnected from power, and power flows to the LED.

The LED can be a signal near the track, or mounted between the rails, or on the front of the facia, or both. Note: The LED is optional and may or may not work depending on the DCC system used. Some DCC systems will shutdown the main line when programming is active leaving the LED unpowered.

Note Regarding the LED
It would be advisable to connect another general purpose diode in series with the LED to protect the LED from being reverse biased when the track signal makes the Cathode more positive than the Anode. LEDs are not designed for high reverse voltages.

Check the switch operation with an ohmmeter to determine how the connections are made before wiring. They usually connect the terminals opposite the handle's position.

Programming Track Boosters

This usually is an issue with Sound equipped Decoders. It will work on non-sound decoders as well.

If attempts to program the decoder result in unwanted changes, or a non-responsive decoder, a Programming Track Booster may be needed to overcome these issues. It would be connected between the command station/booster and the programming track, as per the manufacturer's instructions. Sound decoders arrived after the NMRA defined the DCC standard, so the basic requirements for programming a decoder, while adequate, often do not work with sound equipped decoders which require more current during programming.

This device will often be recommended by the decoder manufacturer when there are difficulties programming the decoder. They are available from your dealer.

A Programming Track Booster serves to make programming more reliable, and may also incorporate short circuit protection and basic diagnotics. It may also provide feedback to aid in troubleshooting a problematic decoder.

NOTE: This device will not solve problems created by the user during installation. It's sole purpose is to make programming more reliable. The device may not be needed, depending on the DCC brand/model chosen by the user. As always, consult the decoder and Program Track Booster manufacturer, or your dealer, to determine if this device would help.

Do I Need a Programming Track Booster?
Model Booster Needed? Notes
Digitrax Zephyr Yes
Digitrax DCS Series Yes
Digitrax DB Series Yes
Lenz LZV100 Yes Firmware greater than Version 3.6 should not require a booster
NCE Power Pro / Power House Yes See Power Pro section below
NCE Power Cab No NCE does not recommend their use.
Zimo No

Programming Track Boosters and NCE Power Cab

DO NOT connect a programming track booster of any kind to an NCE Power cab. The programming track mode of the Power cab is a newer design that incorporates the ability to program sound equipped decoders.

NCE Power Pro Modification

The NCE Power Pro can be modified to increase the track current available during programming.

The outputs are protected from a current overload using small lamps to limit the current. Adding two additional lamps in parallel with the existing ones will double the current.

See Instructions here for more details on this and other modifications.


The PowerPax DCC Programming Booster by DCC Specialties is an older design and may not work with all decoders and command stations. There are timing differences which may be an issue. Soundtraxx's PTB-100 was designed when programming sound decoders became an issue, and addresses the timing problems.

Soundtraxx Tsunami2 and Econami Series DCC Decoders

The Sountraxx Tsunami2 (TSU-2) and Econami series of decoders do not require a programming track booster. Users have reported that attempting to program the TSU-2 or Econami decoders with a PowerPax gives erratic results.

Previous Tsunami sound decoders required a program track booster.

QSI Decoders

A programming track with booster is recommended for best results when programming QSI decoders. A Digitrax PR3 or PR4 will also work.

See also

  1. Decoder Programming - Additional information about programming decoders
  2. Track wiring - Track wiring
  3. PTB-100 - Programming Track Booster by Soundtraxx.
  4. Decoder Tester - Apparatus for testing and programming decoders.

External Links

Note about using a programming track booster with NCE Powercab. (NCE Website)