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Summary: LocoNet is the throttle network designed and used by Digitrax to communicate between throttles, command stations, boosters and other accessories. Interfaces are available to allow a computer to be connected to LocoNet. Several other DCC Manufacturers also employ LocoNet as their throttle network.


What is LocoNet®

LocoNet® is a Digitrax trademark identifying a LAN for model railroads designed and patented by Digitrax Inc. Portions of LocoNet® are covered by US Patent Number 6,275,739. LocoNet can be connected to a computer via a a device such as the LocoBuffer or Digitrax's own PR3, PR4 or MS100 interfaces.

Prior to 2000, the system functioned at less than 20% of available message types and commands that LocoNet is designed for. LocoNet is designed for future expansion, where today's devices will still be able to process messages even it they cannot use it. It is also possible to use a computer with multiple ports to route and bridge messages across several LocoNets, expanding capacity.

For more information on interfacing a computer to your Digital Command Control system, please see Connecting your computer to DCC

Network Details

LocoNet is a networking technology that uses CSMA/CD (Carrier Sense Multiple Access/Collision Detection), similar to Ethernet networking commonly used to interconnect various network devices, such as computers, high speed modems, printers, etc., but optimized for model railroading.

Carrier Sense means that message sync is done within the message stream since all devices on the network see all the messages being transmitted. The devices also know when the network is busy. Multiple access refers to the ability of all devices to access the network and generate messages on their own, without direction from a central controller.

Collision Detection means that when two devices try to send messages at the same time, creating a conflict, that they can resolve those conflicts on theier own.

LocoNet is designed to allow operation at 100% capacity with fewer than one collision in 300 messages, which is less than Ethernet allows.

LocoNet also is similar to the standard ISO Network Model with pipelined multilevel protocol stacks and queues.

LocoNet Basics - An Introduction

Digitrax UT1 Throttle

Loconet is part of a DCC train control system designed by Digitrax to control a model train layout. LocoNet is a Peer to Peer Local Area Network (LAN) designed for very high traffic capacity and free-form wiring as well as future system expandability and ease of upgrade. It is a separate circuit from the track power used to run model trains.

Digitrax developed LocoNet to handle the communications between throttles, stationary decoders, and other devices that need to communicate with the command station. The command station processes, assembles and routes this and other information to either the track or to the LocoNet only. This network allows fast communication between devices not related to running the model trains.

LocoNet B

A LocoNet RJ12 jack may be identified as LocoNet B. It indicates a LocoNet Booster Connection, as part of a booster network. LocoNet B has a limitation of 200mA of current. It is meant to connect the command station and boosters together. Since most command stations are integrated with a booster, this connection is not common. Some command station/booster units made by LocoNet licencees do have the LocoNet B connection.

Loconet T

The LocoNet T jack indicates a higher current is available to power Throttles, stationary decoders and other LocoNet devices. The T indicates a connection for the Throttle Network. Many devices have jacks which are just labelled LocoNet, which are LocoNet T connections.

Digitrax labels the LocoNet connections on their command stations as A and B, both jacks are the higher current throttle type. For programming of the command station, a throttle is connected directly to either LocoNet jack.

LocoNet ID

The LocoNet ID is used with wireless throttles. The default LocoNet ID number is "00." This is not the same as the deprecated Layout ID concept used by NCE.

Any throttle connecting to a UR90, UR91, or a UR92/UR92CE Utility Radio Panel requires a valid LocoNet ID. When a throttle is plugged into the LocoNet it will discover and attach itself to that ID. The throttle will display rA or Ir indicating it has detected a radio or IR device, as well as the ID number. Remember, the wireless features must be enabled on the throttle for this to work.

LocoNet ID allows multiple clubs in close proximity, such as a train show, to use their radio throttles without interfering in the operations on another layout. Note that this is not the same RF interference causing problems with communications between the UR9x and the throttles. This is only to prevent commands from one layout's throttles from being accepted by another layout's receivers.

The throttle must have a 9V battery installed to operate in this manner.

Changing LocoNet ID

It is possible to change the LocoNet ID if there are conflicts. The LocoNet ID number can be changed, either by following the instructions from Digitrax or by using the LocoNet ID tool in JMRI. After the LocoNet ID has been altered, all wireless throttles must be physically disconnected then reconnected to the LocoNet to update the LocoNet ID they connect to. Otherwise the wireless throttle will not work. Tethered throttles are not impacted by the LocoNet ID change.

It is possible to change the ID number using an appropriate throttle if a computer is not available.

LocoNet Details

For more detailed information on LocoNet, see the LocoNet Personal Edition documentation from Digitrax.

As mentioned above, LocoNet is a CSMA/CD system.

  1. Carrier Sense - Devices monitor the LocoNet bus to decide when it is safe to transmit a message
  2. Multiple Access - All devices share the same LocoNet segment, so all messages are seen by all devices
  3. Only one device can be transmitting at a time
  4. Collision Detection - Devices monitor the LocoNet during transmitting, to determine if their message was corrupted by another message
  5. Priority based timing allows a high priority device such as track sensors to transmit their messages with with higher priority than throttles
  6. If two devices attempt to transmit at the same time, both messages are discarded and both devices have to retry. Devices with different priorities should not cause collisions with each other.
  7. A CSMA/CD network characteristic is the rate of collisions increases with network loads above 25 - 50% of the theoretical capability. For good performance load to not exceed the 10-20% of the capacity.

LocoNet operates at a speed of 16.66 kiloBaud, with one start bit, 8 data bits and a stop bit. This structure makes interfacing the LocoNet to a computer's serial port very easy. In fact, several computers may be on a LocoNet.

Throttles are very low priority devices. Their messages are not as time sensitive as those of an occupancy detector. The system will increase their priority as transmission failures increase until the message is successfully sent. Then the priority is reset to its normal level.

More devices means more traffic. Every device that wants to talk waits a specified amount of time after the last message before attempting to send a message itself. After the wait time expires, another slice of time is used to determine priority: High priority devices get the first chance, low priority devices must wait longer before attempting a transmit.

The LocoNet system is a different from the NCE Cab Bus, which is a polled system, meaning "speak when spoken to". As more devices are added to a polled system, response times decline as it takes longer to poll a specific device.

LocoNet Power

The LocoNet system has the following voltages and currents:

  1. The command station has a 15mA pull-up, with a nominal 12V on the DATA signals (This is the LocoNet Termination).
  2. Input impedance of a LocoNet device must be more than 47kOhms. This allows a max draw of 100uA at the minimum voltage.
  3. Minimum voltage is 5V
  4. It would require about 150 LocoNet devices to load the network to its maximum. This is much more than most layouts would have.

What are the Wires used for?

The wires in the LocoNet cable are used for the following signals (referenced to the pins on the connectors).

Pin Signal
1 Rail Sync Positive
2 Ground
3 LocoNet
4 LocoNet
5 Ground
6 Rail Sync Negative

Colours are not referenced, as they can change depending on the cable manufacturer.

Opto Isolated Boosters

Some boosters come with a label stating OPTO or OPTO-ISOLATED. What that means is the LocoNet connections on pins 3 and 4 are isolated through an optical isolation device, and the grounds (pins 2 & 5) are not connected. This prevents currents from flowing through LocoNet's ground wires to return to another booster. They are an extra cost device, and for most applications are not necessary.

As the picture shows, the modules are wired for DCC ou DC, so it is possible the modules are wired for common rail operation to accommodate analog (DC) operations. Never attempt to use analog and digital at the same time on a layout!

LocoNet Termination

Termination is provided by the command station, or a device such as the PR3/PR4. In the absence of a device providing termination, the LocoNet may not work. Termination can also be provided by an external device.

Phone Lines?

A new Digitrax DCC set contains several flat black telephone cables with plastic telephone plugs on the end. The booster/command station (either DCS100, DB150, or Zephyr command station/booster) has 2 RJ type telephone jacks on the front or rear. The throttle also has a cable terminating in a telephone plug. The universal panel (UP5)has two telephone jacks in the front. There may be a short piece of cable with a plastic plug on one end and colored wires on the other end (LT-1).

LocoNet Cabling

Digitrax recommends the use of 26AWG 3 pair such as a flat, 6 conductor 130 Ω ribbon cable with RJ12 6P6C plugs crimped on. This reduces Radio Frequency Interference by balancing the connections. Using pairs of wires reduces the impedance of the cable. The cabling may be branched into a Star or Bus configuration. Using the six wire flat cable, lengths of up to 300m are possible. Depending on the cable's electrical characteristics a total run of Loconet cable can be up to 600m.

Do not loop the LocoNet back onto itself.

Digitrax strongly advises against using Category 5 or 6 Ethernet cabling, as capacitive and inductive issues will introduce problems, especially in long runs. CAT 5/6 wire is designed and carefully manufactured for a specific purpose, and its parameters are not suitable for LocoNet wiring.

Welcome to Digitrax Networking

Digitrax DCS100 Command Station/ Booster

Welcome to the world of Digitrax DCC - where trains are controlled by computer(s).

This is an advanced topic.

The DCS100/ DB150/Zephyr command station is a computer. That DT100/DT300/DT400/UT1|UT1 throttle is a computer. The decoder you just installed in your loco is really a computer. Digital Command Control is all about computers. If you are familiar with computers, especially networked computers at your school or office, you are well on your way to understanding DCC.

If you're not familiar with these terms, please see our layman's explanation of DCC.

Computers talk to each other through data communication lines. Typically these lines are similar to a telephone line - either a flat-ribbon cable like the line to your telephone set, or a thick cable like the one behind the wall into your telephone jack. In computer language, this type of wiring and the signals that travel through the wires form a Local Area Network or LAN. Industry standards which specify the details about these signals, which wires in the cable they travel through, what the colour of the wires should be, the type of connector plugs to use, and other things.

Digitrax's throttle network is a Local Area Network that is not very different from a computer LAN. Except that, instead of calling their Local Area Network a "LAN", Digitrax calls it a "LocoNet" That's all the LocoNet is - a Local Area Network, optimized for use on a model railroad. That is why you've got a whole bunch of stuff that looks like telephone cables, plugs, and jacks. We won't get into the mysteries of what types of signals go down these wires - because we don't have to. We're more interested in installing those cables/jacks so that we can get to running the trains. What we'll do over the next few sections is introduce some of these wiring standards, show how to wire the LocoNet and, in the process, try to take some of the mystery out of LocoNet.

LocoNet Interface Devices

To comunicate between a computer and the Loconet, you need a translator that will understand both of them. There are two options available: the Digitrax interface and the third party Locobuffer.

The current Digitrax solution is the PR4

  • PR4
  • Multifunction USB to LocoNet connectivity.
  • MS100 - Digitrax' own computer/Loconet interface device.
    • Has been significantly outdated by the LocoBuffer II
    • Connects via RS-232. Some users report RS-232 <-> USB adapters work.
    • It has now been discontinued. Its replacement is the PR3.
  • PR3
    • Discontinued
    • Replacement for MS100
    • Uses USB-2.0 for connection to computer.
  • Locobuffer - Third party hardware interface device
    • History
      • Developed by John Jabour in response to speed and platform restrictions of the MS100. Technically was not much better than the MS100
      • Was available in complete or kit form from the designer until he decided not to make them available any more.
      • Manufacturing of the unit to was transferred to RRCircuits.
      • Original Locobuffer is no longer available.
  • LocoBuffer II - Developed by RR-CirKits as a replacement to the original LocoBuffer.
    • Faster, smaller, and more up to date.
    • Certified by Digitax
    • Connects via RS-232. Many users report RS-232 <-> USB adapters work well.
    • Faster serial connection, fewer dropped packets.
  • LocoBuffer-USB - Developed by RR-CirKits as a replacement to the LocoBuffer II
    • Replaces LocoBuffer II
    • Connects directly to USB port
    • Powered from USB connection and Rail Sync lines, no external power supply needed.


  • DB-25 serial RS-232 input
This unit is obsolete. Originally released in 1996.

From the Digitrax Website:

The MS100 Computer Interface is designed to let an IBM compatible computer with RS232 communications port monitor Digitrax LocoNet. The MS100 is a signal level translator between LocoNet and a 25 pin DB25 style RS-232 port. It is basically a dongle that plugs into the 25 pin RS-232 serial port, with an additional cable connecting to LocoNet.

Application software running in the computer can then interpret the activity on the LocoNet and report back to the user via the computer screen. The interface was primitive, passing all messages to the computer, which results in additional overhead.

Digitrax PR4

The PR4 supersedes the PR3.

  • Multifunction USB to LocoNet.
  • Optimized for Direct mode
  • LocoNet is Electrically Isolated from USB port.
  • “SoundLoader” decoder compatible.
  • Programs most DCC decoders.
  • Standalone operation: No requirement for a Digitrax Command Station.
  • LED status lights.
  • Opto-isolated.

Works with Mac and MS Operating Systems. PR4 software is MSWindows only, JMRI compatible (MacOS).

(Dec. 2017)

Digitrax PR3

  • USB-2.0 input
  • May be used with Digitrax' "Soundloader" program (currently Windows only).
  • Compatible with Windows 2000, XP, and Vista (Windows 7 status currently unknown)
  • Compatible with JMRI on Mac OS 10.4/10.5 and Xubuntu 10.10
  • Only requires a power supply for use with "Soundloader" program.
  • LocoNet® terminator included.
  • Software configured
  • Not Opto-isolated.


LocoBuffer II

LocoBuffer-II specs:

  • DB-9 serial RS-232 input
  • Opto isolation (if not using LocoNet® powered mode)
  • Buffered input and output allows use with all operating systems. (Linux, Mac, MS Windows)
  • Hardware handshaking using RTS/CTS (also includes DTR/DSR turnback required for MS Windows XP)
  • Packaged unit size 1-1/2" x 3-3/4" x 3/4"
  • Ready To Run
  • Optional Package available with cables, (DB-9 or Mac DIN-8, and 14' LocoNet®) plus 9V power supply
  • LocoNet® terminator included. Rev-f terminator is built in. (Allows you to use your LocoBuffer-II to add LocoNet® device compatibility to other systems)
  • DIP switch settings for all options
  • MS-100 compatible plus 19,200 and 57,600 standard Baud rates
  • Serial Boot Loader programmable for upgrades (Does not require special hardware)
  • Power from 9V-12V AC-DC
  • Optionally LocoNet® powered from rail sync lines
  • Digitrax LocoNet® certified.
  • Suggested Retail Price: $69.95.

LocoBuffer-USB Features:

  • USB 2.0 to LocoNet® interface
  • Optical isolation between USB and LocoNet® prevents potential grounding problems
  • Buffered inputs and outputs allows use with all USB supported operating systems
    • CD with drivers for Linux 2.4, Mac OS-9, OS X, MS Windows 98SE, ME, 2K, XP
  • Packaged unit size just 1-1/2" x 3" x 3/4"
  • Ready to run unit
  • Internal LocoNet® terminator.
    • Allows a LocoBuffer-USB to add LocoNet® device compatibility to other systems
  • 57,600 Baud interface speed
    • No jumpers or switches to set
  • Compatible with existing software
  • Installs as a serial port
  • Hardware handshaking using RTS/CTS
    • Includes DTR/DSR turn back required by MS Windows XP
  • Boot Loader for firmware upgrades
    • Does not require special hardware to install upgrades
  • Powered directly from USB and LocoNet® Rail Sync lines
    • No external power adapter needed
  • Internal option connector allows for future features
    • Planned optional programming track output
  • Includes 3' USB A-B and 14' LocoNet® cables
  • Suggested Retail Price: $ 74.95

LocoNet USB Interface 63120 by Uhlenbrock

The USB-LocoNet Interface build by Uhlenbrock Elektronik GmbH offers a number of advantages advantages. As with the LocoBuffer-USB, it uses a microcontroller for exact LocoNet timing, reducing the load on the computer.

  • Opto-isolated
  • Modes:
    • LocoNet Direct
    • Only valid LocoNet messages are passed to the computer

L.Net Converter - ESU

ESU has added the L Net Converter or ECoS Throttle Integration Adapter.

It will allow connection of LocoNet throttles to an ESU command station such as the ECos. This will allow you to keep your existing LocoNet devices, such as feed back modules, as well as your Uhlenbrock or Digitrax throttles.

This device works with the ECos or the older Central Station (60212) command stations.

Feedback Modules

Loconet modules such as those for track occupancy detection. The L.Net Converter allows those devices to connect to the ECoS, for activating routes or shuttle train control. Use of s88, Loconet and ECoSDetector feedback modules is possible at the same time.


The L.Net Converter solves the communications problem: the ECoS will send loco and turnout commands via the L.Net Converter to the devices connected.

Ethernet to LocoNet

  • Ethernet to LocoNet interface with integrated Power supply.
  • Optical isolation between computer and LocoNet.
  • Running with Rocrail
  • Do It yourself package or Pcboard is available
  • IP adress selectable via EEprom settings
  • Suggested package price €65,-- , pcboard only €9,--
  • Pcboard is double sided with silkscreen and soldermask. Through hole connected.
  • Look at http://wiki.rocrail.net/doku.php?id=mgv101-en

LocoNet Construction

Network Topology

LocoNet can be arranged in a number of ways: Star, Tree or Linear.

LocoNet should not be arranged into a loop, as it is very important to make sure the RAIL SYNC signals are connected correctly and in sync. Otherwise they will cancel out. For this reason Digitrax does not recommend wiring LocoNet in a loop.

Making a LocoNet cable is easy. Wiring a socket is not easy, and can introduce problems. You also do not have to follow the example of the cable with RJ12 plugs, but it is important to get the wiring correct to avoid problems.

LocoNet Splitters

There are a number of ways to split your LocoNet. Passive splitters will work, but they must be straight through in design, not those that flip connections. While this may work with a telephone, it causes problems with LocoNet.

Splitters, such as the Digikeijs DR5097 DigiNetHub, are designed specifically for LocoNet.

For best results, power the Utility panels (UPx) to maintain signal strength. Do not use the front jacks to split the LocoNet, as they often replace the rail sync signals with power for the throttles.

Digitrax UP6Z

The UP6Z is a LocoNet splitter, which has six jacks, two on the rear and four on the front.. It is also used to reduce track voltage for Z scale model railroads, allowing the track bus to be supplied by a lower voltage than the Digitrax booster can provide, at a maximum of 3A. This feature is optional, so the UP6Z can be used with any scale.

The device doesn't not require power to operate. It has a power plug, but it is just there to fill a hole in the cover, and doesn't connect to anything. It also has no battery saver circuitry.

Standalone LocoNet

It is possible to construct a standalone LocoNet, without a command station functioning as the Master. As the command station also provides termination to the LocoNet, this will need to be provided. Devices such as the PR3 and PR4 can do this, or it can be constructed using a power supply. In this arrangement LocoNet devices can communicate amongst themselves.

LocoNet Troubleshooting

Also see the Digitrax Hints page for a list of Audible Alerts

Construction Issues

Many LocoNet problems are not really a LocoNet issue, but mechanical or electrical issues with the cabling.

Break in LocoNet Signal

One issue is that the LocoNet signal from the command station is only present on one of the two LocoNet (red and green) wires. Usually the command station provides the LocoNet signal on Pin 3 (the red wire). At some point a device, such as a throttle, will bridge pin 3 to pin 4.

Devices such as a throttle, the LNRP or a UP92 will provide this bridge. The DT400 is known for not bridging pins 3 and 4. Another culprit is the UP5.

The LT5 LocoNet Tester can be used to determine if bridging is taking place, and then be used to find out where the bridging is occuring. It can also determine if the LocoNet signal is on the red wire before the bridge.

If a downstream booster stops responding, it is possible there is a break in the wires carrying the LocoNet signal from the command station. If there is a utility panel connected between the command station and the booster, and this problem only appears when a throttle is unplugged, one of those cables has an issue. Removing the throttle from the panel disconnects the bridge between wires 3 and 4.

If there are multiple panels between the command station and the booster, any one of those panels can be used to bridge the two LocoNet wires. Using a throttle you can isolate the cables involved by testing each panel until the issue appears.

If there is no command station on the LocoNet, a LocoNet termination can also connect lines 3 and 4.

Crimping Issues

Improperly crimped connections are common. It is important to use the correct type of connector and a good quality crimping tool.

There are two types of RJ connectors available on the market depending on the wire type:

  • Solid Wire
  • Stranded Wire

Using a solid wire RJ connector on a stranded wire may work, but it is not reliable. If it were, there would only be one RJ connector for both types of wire. Using a connector meant for stranded wire to terminate a cable with solid conductors will introduce issues as there are two prongs which penetrate the insulation, resulting in the potential for the wire to break at that point. Nicks in solid wire weaken the wire.

Incorrectly crimped terminations may result in a cable which "tests good" with an LT1, but not work with LocoNet devices.

Troubleshooting a LocoNet Cable


Using a DMM, measure the voltages on the cable, referencing the Ground terminal on the command station.

  • A healthy working LocoNet should have 10V or more available between ground and pins 3 or 4 of the RJ connector.
  • A cable with a poor, high resistance connection will see a reduced voltage on the pin(s).
  • The voltage should be 9 to 10V on those pins.

LocoNet Wiring Standards.jpg

Rail Sync

The Rail Sync wires (the outer pins on the RJ connector) can become an open circuit, without having an adverse effect on many of the devices they connect. The Rail Sync is a low voltage/low power representation of the track signal. Your DMM can pinpoint the issue. These signals are not in phase, so do not short them together.

Digitrax Zephyr Specific

With a DCS100 integrated command station/booster or DB150 booster, only one of the LocoNet wires (3 and 4) is driven. Connecting a throttle shorts them together.

In most LocoNet implementations, the two LocoNet wires are paired together. Throttles, DS54s, and the LocoBuffer all pair pins 3 and 4.

In some situations this may not happen. Should a LocoNet device not work, this can be the issue. A common culprit is the DCS series Zephyr when connected to LocoNet devices. A Zephyr internally connects the two wires via a resistor. The devices do not work as the signal is missing.

The solution can be a shorting plug, made from an RJ connector. A wire is fitted to connect between pins 3 and 4, which is then crimped in place. The shorting plug can then be inserted in any available spare LocoNet jack, which should resolve the problem.

LocoNet Termination Issues

LocoNet Termination for this discussion refers to the supply of power to the Rail Sync lines. If you are looking for terminations on a power bus, please refer to the Bus Termination page.

Some devices may not work if the LocoNet is not terminated correctly. Many LocoNet devices rely on the Rail Sync wires for power. A low current 12VDC source can supply this for a standalone LocoNet. Another function of the termination device is the connecting of pins 3 and 4 together. For a standalone LocoNet implementation, a small 12V power supply is used to provide power to the rail sync lines.

A number of devices, such as the PR3 can also provide LocoNet termination.

A Ultility Panel can also supply power on the Rail Sync lines.

Digitrax LT1

The LT1 is included with all Digitrax Starter Sets. It consists of a harness with 6 conductor Telco type wire and a male plug, a tester with a female 6 conductor jack and a protection resistor. The LT1 can be used to test LocoNet cables, as well as mobile decoders.

The LT1 uses RailSync power to check the cables. Do not leave it connected as it can destabilize your LocoNet. Cable verification is done by plugging the cable into the tester, and the other end to a Universal Panel (UP-x) to connect it to the LocoNet for power. The four LEDs should light.

As the LT1 is not a LocoNet device, it should not be left connected during normal operations.

  • If two LEDs on one side don't light, there is a problem between them and the LocoNet common line on that side.
  • The two inner LEDs are the data lines. If they do not light, the LocoNet is in sleep mode or there is a problem. If only one lights, plug in a throttle and both should light. (Remove any battery from the throttle first.)
LED #1 
Rail Sync + (Positive), White Wire, 6.2V
LED #2, 
LocoNet Data 1, Red Wire, 14.5VDC
LED #3, 
LocoNet Data 2, Green Wire, 14.5VDC
LED #4 
Rail Sync − (Negative), Blue Wire, 6.2VDC

LocoNet voltages are measured using pairs 3 and 4 for one polarity, and 5 and 6 for the other.

The network becomes unstable at voltages less than about 7VDC. At the command station, with no other cables connected, you should measure 14 to 14.5VDC. If there are low voltages, disconnect all the cables and begin by reading the voltage, then connecting a cable, check the voltage, connect the next cable/device until you find the problem.

Don't leave the LT1 plugged in. It is a testing device, not a monitor. Two LT-1s can actually destabilize or crash your LocoNet.

Rail Sync

Low voltage Rail Sync signals are also present on the cables. Check for them using the LT1. The two outer LEDs must be bright, and constantly lit. If not, work your way through the network until the offending cable is located.

For proper operation of the booster, all four LEDs should be lit.

This is not the same as a booster phase issue.

DCS100/DCS200 Command Stations

The NET indicator on the DCS100/DCS200 Command Station is a Red LED that displays information about what the Command Station sees on LocoNet. When your LocoNet is wired and operating properly, the NET indicator will be on and flickers any time a valid LocoNet message is detected by the Command Station. The following table explains the various patterns for this indicator:

Solid Red 
ON, Blink OFF 
Valid LocoNet Message detected.
LocoNet is possibly shorted
Blinking every half second 
The command station is in Option Set mode.

LocoNet Repeater (LNRP)

For large complex layouts, Digitrax offers the LNRP LocoNet Repeater. It allows the creation of two LocoNets: One protected, one unprotected. The protected one is used to connect boosters, etc, while the unprotected network is used for throttles. This protects the layout from a network crash, often caused during throttle connect/disconnect operations.

The LNRP has diagnostic LEDs to help troubleshoot network problems.

LocoNet & RailSync Voltages

If either voltage is low, the layout may experience several different symptoms.

  1. Difficulty turning on track power to additional Boosters.
  2. Throttles may not operate correctly or may have no display at all if they do not have a battery installed.
  3. Detection and/or Transponding may not operate correctly.

Use a good quality Digital Voltmeter (DVM) to help diagnose:

  1. If the 2 LocoNet data lines (pins 3 & 4, green/red) have voltage between 8V and 14V with no message traffic present. This confirms that the booster is outputting enough voltage.
  2. If the RailSync lines are OK. The two RailSync lines are a differential of the track digital signal, and are driven with a 22 ohm output impedance so as they are loaded the voltages will drop, indicating the current load. These two lines should not be connected together, and this will cause excess current draw and low voltages.

Differential means that if signal A is HI, the corresponding signal will be low. This allows the pair to be summed together (A+ (−B)) while cancelling any noise.

How to Check for LocoNet Voltages

Prepare a short LocoNet cable with one end stripped to expose the wires inside the jacket.

  1. Strip the Red and Green wires and twist them together.
  2. Strip the Black and Yellow wires and twist them together.
  3. Plug this short LocoNet cable directly into one of your command station’s LocoNet Ports.
  4. Disconnect LocoNet from the layout at your Command Station so that you are measuring LocoNet voltage at the Command Station without the layout attached.
  5. Use a good quality multimeter (in the 20 volt DC range) to measure the DC voltage between the red/green and black/yellow pairs.
  6. Connect the red/green wires to the +ve lead of the DVM and the –ve DVM lead black/yellow wires and measure the voltage.
  7. The voltage on the LocoNet data wires should be at least +8V DC. The highest voltage depends on the command station but is usually +12V to +14V.
  8. Very large layouts will benefit from using a LocoNet Repeater (LNRP)
If more than 40 devices are on a single leg of LocoNet, or you get frequent interruptions as you plug in devices, this may indicate the need for an LNRP.
  • LocoNet Repeaters can be used to isolate areas of the layout from each other
  • Allows for troubleshooting with LocoNet fault indications
  • Proper operation of LNRP REQUIRES at least a 14VDC power supply.

How to Check RailSync

Use the short LocoNet cable prepared for checking LocoNet voltage above.

  1. Plug this short LocoNet cable directly into one of your command station’s LocoNet Ports.
  2. Disconnect LocoNet from the layout at your Command Station so that you are measuring RailSync voltage at the Command Station without any of the layout Loconet attached.
  3. Measure the no load RailSync voltage at the Command Station without the layout plugged in. Measure both RailSync voltages separately and add them to remove and analog zero stretching changes and to be sure both wires are carrying RailSync.
  4. Use a DVM to measure from the white wire pin1 to black or the yellow ground (pin 2 or 5).
  5. Use a DVM to measure from the blue wire pin 6 to the black or yellow ground (pin 2 or 5).
  6. Add these two DC voltages, the total should be +12V to +14V DC, with the command station unplugged from the layout. This is the unloaded RailSync measurement.
  7. Measure the Loaded RailSync Voltage at the Command Station with the layout plugged back in to the Command Station
  8. Plug the LocoNet Cable from the layout in to the Command Station.
  9. Use a DVM to measure from the white wire pin1 to the black or yellow ground (pin 2 or 5) on the short LocoNet Cable plugged in to the Command Station.
  10. Use a DVM to measure from the blue wire pin 6 to the black or yellow ground (pin 2 or 5).
  11. Add these two DC voltages, the total should be +7 volts DC, with the command station plugged into the layout. This is the loaded RailSync measurement.
  12. Compare the Unloaded and Loaded measurements for RailSync; this voltage difference is a measure of how much power the RailSync loads are drawing.
  13. If voltage is below 8 volts, make sure all UR92s, UR91s, PM42s, etc. are powered using PS14 or similar power supplies as required.
  14. If this does not bring the voltage above 8 volts, power all throttles with batteries and/or power UP5 and similar panels using PS14. Multiple UP panels can share a single power supply by daisy chaining them together as shown in their instruction sheets.

The Digitrax RJ12 LocoNet Wiring Standard

Digitrax UP5 Panel

Somewhere in the instruction manual, it says that "The RJ12 is the 6-pin version of the RJ11 connector with all pins loaded with conductors. This is the connector that Digitrax uses for LocoNet." At which point, your eyes start to glaze over and you go off into a trance. Now before you go into a coma, let's back up a bit. You're familiar with your telephone set and the cables and plugs that go into the telephone set.

On the previous page, we've shown you some of the Digitrax components that use these components. The LocoNet consists of the same type of wires and connectors - used in your telephone system - with one very important difference. Your telephone cables may have 2 or 4 small wires covered by that grey, black or white plastic insulation. The Digitrax LocoNet uses components that use 6 wires. Here's what this type of cable looks like. It's really not much different from the cable that goes into your telephone set.

The telephone/data communications industry calls this an "RJ12 6-wire standard". RJ12 components consist of 6-wire telephone cable, 6-wire male plugs and 6-wire female jacks. You can have many different combinations of these components.

  • Male plug to flat cable to male plug.
  • Male plug to flat cable to female jack.
  • Male plug to two female jacks - all in one plastic assembly.
  • Female jack to Female jack - all in one plastic assembly (sometimes colloquially called a gender-bender).
  • Female jack in a wallplate or two female jacks in a wallplate
  • Male plug to flat cable to two female jacks (I call this a double-female extension cord)

This is what some of these components look like.

If you have a Digitrax system, six wires are very important. Anything less and it will not work.

Here are the wiring standards, wire colours, functions, and pin-outs for the Digitrax RJ12 6-wire LocoNet. (If you're using Lenz, Atlas, NCE, or any other system, check your user manual.) Note the relationship between the Pin Number, the colour of the wire inside the cable, the function, and the voltage.

LocoNet Wiring Standards.jpg

If you look at the front of the male plug with the locking tab on top, you'll see that the White wire (Pin 1) is on the left, and the Blue wire (Pin 6) is on the right. If you look at the front of the female jack, you'll see that the White wire (Pin 1) is on the right and the Blue wire (Pin 6)is on the left.

The wires form two mirror images of three wire sets. This eliminates polarity and mating issues.

If you visually connect the male plug to the female jack, you'll see that the white wire of the male plug connects to the white wire of the female jack, the black wire connects to the black wire, the red to the red, the green to the green, the yellow to the yellow, the blue to the blue. This is sometimes referred to "Pin 1 to Pin 1, Pin 2 to Pin 2, Pin 3 to Pin 3, Pin 4 to Pin 4, Pin 5 to Pin 5, Pin 6 to Pin 6" wiring - or "Pin 1 to Pin 1" wiring to keep it short. It will help in troubleshooting if you always make sure that each coloured wire connects to its own colour. Also note that

  • The white wire (Pin 1) has the same function as the blue wire (Pin 6) - Rail Sync
  • The black wire (Pin 2) has the same function as the yellow wire (Pin 5) - Ground
  • The red wire (Pin 3) has the same function as the green wire (Pin 4) - LocoNet

A Loconet cable has two grounds and LocoNet lines, so the parallel communication lines reduce the effective loop resistance. This means longer runs of cable. If a wire should break or create an intermittent connection, the network will still function.


The two outside wires, white and blue, each carry a copy of the master packets transmitted by the command station to the rails, are called RAIL SYNC. These two wires carry opposite polarity signals, and are transmitted differentially in the same cable, so RAIL SYNC can drive a booster feeding a power district hundreds, if not thousands of feet from the command station.

The transmission method reduces the problems related to electrical noise and interference, resulting in a very reliable signal in what would be a very noisy environment.

RAIL SYNC also allows you to power low current power draw devices, such as LocoNet input sensors (utility panels such as the UP5) or utility throttles without internal power sources. Devices such as the UR92 Radio receiver draw too much current so they must be powered externally. Even so, it is advisable to power some Utility Panels with their own power supply.

The utility panels use diodes to power to the front and side jacks. As there is no RailSync present on those jacks, a booster cannot be connected to them. The external power supply allows more power to be supplied to the front and side jacks to power throttles. This power is local only, and is not supplied to other panels via the rear jacks, unless a link is installed (per Digitrax instructions.)

Benefits of the Cable Construction

Since the six conductor LocoNet cable is balanced, and the signal propagation is arranged in a manner to minimize RFI (Radio Frequency Interferenc), LocoNet transmissions should not cause problems with radio and TV reception. It also minimizes the susceptibility of LocoNet to EMI from power tools and radio transmitters such as wireless phones or garage door openers.

Making a LocoNet Cable

Crimping pliers for RJ connectors
Uncrimped connector

So, if you happen to crimp a male plug onto the end of a cable the wrong way, it won't affect the operation of the LocoNet because the corresponding wire at the other end (blue - white, yellow - black, green - red) both have the same function. (It's not necessary to understand what Rail Sync, Ground, or LocoNet functions are.) However, we highly recommend that you make sure that Pin 1 is connected to Pin 1..... Pin 6 is connected to Pin 6.

  • Note: Crimp-on connectors are made for stranded or solid wire. Use the correct type for the wire you have. Using the wrong type will result in cable problems later.
These RJ connectors show the differences between wire types: Solid Wire on the left, Stranded on the right.

Here's that cable we showed you at the top of the page. You'll note that, in order to keep the Pin 1 to Pin 1 orientation, we have to put a twist in the cable.


Actually what we do is crimp one of the male plugs with the tab on top of the cable and crimp the other male plug with the tab on the bottom of the cable. The Digitrax manual shows it something like this.

This is also called a Data Cable, but for this application it is a LocoNet cable. Note the alignment of the plugs as indicated by their tabs.

We'll show you a little trick to help you keep that orientation when it comes to crimping on those male plugs-- Hold the plugs tab side down so you can sort of see the wires through the plastic. Hold the plug with the opening toward you, and as you slide the stripped ends of the cable into the plug, make sure that the blue wire is on the right side of the hole. Do this at both ends and you're all set!

If you want to verify that a cable is wired correctly, hold both plugs next to each other, tab down. If the colors on both plugs are in the same order (white-x-x-x-x-blue) your cable is crimped correctly. Now use the cable tester and make sure it works electrically!

Oh-- if you happen to goof up and both plugs show (blue-x-x-x-x-white), don't worry-- As long as -both ends- of the cable match it'll work OK.

After making a LocoNet Cable, test it with the LT1 LocoNet Tester that came with your set.

Using CAT5/CAT5e/Cat6 Cables

Digitrax neither supports nor recommends using CAT5 or CAT6 for LocoNet wiring.

Cables Types Not Recommended

As mentioned above, Digitrax does not recommend using Ethernet cabling.

CAT5, CAT5e, CAT6, Shielded Twisted Pair, and serial cable is not recommended as the impedances are engineered to work with Ethernet frequencies, not LocoNet. These types can cause erratic operations.

The best cable type is the flat, six wire telephone cable. With this type of cable runs up to 2000 feet are possible. This type of cable is readily available and not expensive. A specialist electronics store serving technicians and hobbyists is the best source for wire and RJ12 connectors. They also sell the proper crimpers for making these types of cables.

LocoNet Wiring: Theory

Digitrax recommends using the 6-wire configuration for the following reasons:

In a 6 wire flat configuration, the left 3 wires are effectively a "mirror" image of the right 3 wires.

There are 2 Ground (pins 2 & 5) and 2 LocoNet data connections (pins 3 & 4), so the effective "loop resistance" is lower because of paralleled wires. This lets LocoNet run over greater distances.

If one ground or signal connection is broken or intermittent, the network can maintain a reliable connection.

The two outside wires (pins 1 & 6) carry signals of opposite polarity (differential signalling) compared to the master system rail packets, this is called RailSync. RailSync allows LocoNet boosters and other LocoNet devices to be connected anywhere along a cable run. This works even with cable runs of thousands of feet and in the presence of noise and interference.

The balanced nature of the cable and the way the signal currents propagate in this "RF Quad" configuration generate the lowest possible RFI radiation and EMC susceptibility or inward interference pickup. This is a good thing. This is part of the reason Digitrax LocoNet handily passes the FCC Class B radiation Certification requirements.

LocoNet’s philosophy and architecture allow "free-form" wiring with no termination or "linear-bus" restrictions. You can star, tee, branch, or expand LocoNet in any configuration. LocoNet can be used in any configuration except for a ring. NEVER connect LocoNet back on itself, because pins 1 and 6 should not be connected.

LocoNet Wiring: The Specifics

  1. LocoNet supports a total cable length of up to 2000 feet depending on actual wire type used and its capacitance.
  2. No two devices should be connected by more than 1000 feet of cable.
  3. LocoNet can be split & branched in any free form style.
  4. The only network current pull up termination needed is provided by the Command Station. There should be only one Command Station the layout.
  5. Do not loop LocoNet back on itself. Looping LocoNet back on itself causes RailSync (pins 1 and 6) to be shorted together. This causes it to look like an overload to the driver circuit.
  6. LocoNet works best when the network cables are 22AWG to 28AWG. The recommended 6 wire flat telephone type ribbon cable is 26AWG.
  7. Plug and play design using 6 wire telephone type cables and RJ12 jacks makes setting up LocoNet quick and easy.
  8. Plug in your LocoNet Cables in the same pin orientation around the layout for best results.

LocoNet Wiring: Cables

LocoNet Cables must be reliable and well made, or you may see intermittent connectivity and erratic operation on the layout. If areas of the layout exhibit intermittent issues, bad cables may be the problem. Bad cables on your layout can be very frustrating and are completely avoidable by simply testing each cable before you install it on the layout.

It’s easy to make LocoNet Cables. If you would rather purchase them, ready-made 6-pin male RJ12 to RJ12 cables of various lengths are available from Digitrax and other sources such as DigiKey and Mouser. Be sure to use 6-conductor and not the similar 4-conductor plugs and wires. If you purchase pre-made cables, make sure you test them as described below before using them.

LocoNet Limitations

The limitation to LocoNet are:

  • Distance - May have a total parallel cable length of up to 2,000 feet, with no point-to-point length exceeding 1000 feet.
  • Max number of devices? - That depends on the current draw in the LocoNet but that can be quite a technical subject. For modellers who use Digitrax systems at home, they will never reach that limit. However, if you belong to a MR Club with a large layout and many throttles in use, you can experience some problems.

RJ Information

RJ stands for Registered Jack - as in telephone jack - as registered with the Federal Communications Commission (FCC) by the telephone industry when plastic modular components were developed in the 1950s/60s. Later on, as data communications technology developed, the telecommunications industry added to these standards. The RJ standards don't refer to the physical size of the male plugs or the female jack. They refer to the way the jack is to be wired and what the wiring is to be used for.

To confuse things even more, the RJ standards specify the number of conductors (wires) going into the plug or jack and the number of positions available in the plug or jack to anchor these wires to. For example, the RJ12 LocoNet plugs and jacks we use are specified as RJ12 6p6c. That is, 6 positions are available to anchor the wires (the 6p). And 6 conductors (wires) can be wired into the plug or jack (the 6c). And all of this wiring is to be used for a Local Area Network (LAN) - which we call the LocoNet.

Standard Use Positions VS Conductors Authority Plug Width Jack Width
RJH Telephone Phone Head Set 4p4c FCC 0.299" 0.355"
RJ11 Telephone Phone Single Line 6p2c FCC 0.375" 0.383"
RJ14 Telephone Phone Single Line 6p4c FCC 0.375" 0.383"
RJ12 LAN/Printer network 6p6c Industry 0.375" 0.383"
RJ25 Same as RJ12 but for stranded cable 6p6c Industry 0.375" 0.383"
RJ45 LAN/Data network 8p8c Industry 0.492" 0.459"

The columns for "Plug Width" and "Jack Width" aren't part of the standards. To remove some confusion, I took my digital caliper and measured these plugs. RJ11 RJ14, RJ12, and RJ25 have the same Plug and Jack Widths. But only RJ12 and RJ25 have the number of cables/positions we need for our LocoNet.

Parts Suppliers

Here is a listing of websites where you can order pre-made cables. The downside is that you're stuck with whatever lengths you find. There is also a list suppliers for bulk cable, connectors, crimpers, and end pieces. This will allow you to make cables of any length.

Premade Only:


Supplier Name Shiping Locations Types of Products
-- C   C   C--
Cable Wholesale US Based, International Shipping Bulk cable, premade cable
-- D   D   D--
DigiKey US Based, International Shipping Bulk cable, premade cable


Supplier Name Shiping Locations Types of Products
-- A   A   A--
Action-Electronics ? Cable Connectors
-- M   M   M--
My Cable Shop US Based, International Shipping Cable Connectors

LocoNet Licences

Digitrax maintains a list of Licencees of Loconet

DCC Systems Employing LocoNet

  1. Digitrax, the owner and creator of LocoNet
  2. Digikeijs, a Dutch manufacturer of Loconet Products including command stations and occupancy detection devices
  3. Uhlenbrock
  4. Fleischmann
  5. Massoth

Some also produce LocoNet compatible hardware

Software Licencees

A number of companies have licensed the LocoNet software. JMRI is an example of a LocoNet Licensee.

Do It Yourself Solutions for LocoNet Interfaces

A few solutions exist for "roll your own" interfaces.


LocoLinx on Arduino UNO with FremoLNShield

Supports Hardware Handshaking. Requires a LocoNet Shield

Webpage with more information.

LocoLinx on Arduino Duemilanove with Loconet Shield on Proto Shield

This one is outdated and may be difficult for find

Suports hardware handshaking via the CTS line. Incorporates a genuine FTDI USB IC, less issues with drivers. (The LocoBuffer USB also uses this IC.) Duemilanov

Webpage with more information.

There is more information on LocoNet interfaces available on the LocoNet over TCP webpage.

ArLoco from ARCOMORA

The ArLoco is an Arduino Shield 16 (UNO) or 58 (MEGA2560) channel feedback encoder with LocoNet interface.

Supports LocoNet-T and LocoNet-B. Has two LocoNet RJ12 jacks.

For more information see their website.

Model Railroading with Arduino LocoNet Interface

This site has details on a LocoNet interface. Construction details are here.

There are a number of other projects on that site as well.

Iowa Scaled Engineering

DCC Decoder Shield for Arduino

The ARD-DCCSHIELD is an optoisolated interface shield for connecting an Arduino (as a decoder) to a model railroad DCC control system. It cannot act as a command station.

NMRA Digital Command Control (DCC) Library

This library allows you to interface to a NMRA DCC track signal and receive DCC commands.

The library currently supports the AVR ATTiny84/85 & ATMega88/168/328/32u4 and Teensy 3.x using the INT0/1 Hardware Interrupt and micros() ONLY and no longer uses Timer0 Compare Match B, which makes it much more portable to other platforms.

Download the NMRADCC library from GitHub.

See Also



LocoNet Personal Edition