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LocoNet was designed by Digitrax and portions of LocoNet are covered by US Patent Number 6,275,739. LocoNet can be connected to a computer via either a LocoBuffer, Digitrax' own Product:PR3 or Product: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

What is LocoNet

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.

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.

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 Details

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.

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
  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.

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 Product:DCS100, Product:DB150, or Zephyr command station/booster) has 2 RJ type telephone jacks on the front. The throttle also has a cable terminating in a telephone plug. The Product:UP3/Product:UP5 panel 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). What's all this telephone stuff about?

Digitrax recommends the use of six wire flat cable with RJ12 plugs crimped on.

Welcome to Digitrax Networking

Digitrax DCS100 Command Station/ Booster

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

The DCS100/ DB150/Zephyr command station is a computer. That Product:DT100/Product:DT300/Product:DT400/Product:UT1 throttle is a computer. The decoder you just installed in your loco is really a computer. DCC 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 are a Local Area Network or LAN. You may not realize this, but there are industry standards which specify the details about what these signals do, which wires in the cable they travel through, what the colour of the wires should be, the type of connector plugs to use, and a whole bunch of other things. These standards are part of the LAN.

Digitrax DCC is a Local Area Network that is not very different from a computer LAN. In fact, the standards are very similar. 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. And that's 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. All we have to know is how to connect these components together. We're more interested in installing those telephone cables/jacks so that we can get to running the trains. What we'll do over the next few pages is to introduce you to some of these wiring standards, show you how to wire in the LocoNet, and, in the process, try to take some of the mystery out of this wiring.

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.

(Insert photos of Product:UP3/Product:UP5 panels, telephone jack and cable components for example: Two RJ12 Female Jacks in a Wallplate RJ12 Male Plug to Flat Cable RJ12 Double-Female Extension Cord RJ12 Female-Female Gender Bender)

If you have a Digitrax system, 6 wires are very important. Anything less and it won't 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, 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 phase 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,


Since the six conductor LocoNet cable is balanced, and the signal propagation is arranged in a manner to minimize RFI (Radio Frequency Interference", 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.

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 phase. 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 Troubleshooting

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

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.

You can also use the LT-1 Tester, all four LEDs should be lit, three if a throttle is on the network. The outer LEDs are Rail Sync, the inner LEDs indicate LocoNet.

Don't leave the LT-1 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 LT-1. 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 out of phase issue.

LocoNet Repeater

For large complex layouts, Digitrax offers the LNRP LocoNet Repeater. It allows you to create 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.

Making a Cable

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.

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.


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

Digitrax does not offical support using CAT5 for loconet wiring. Use at your own risk.

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.

Many layouts use CAT5/CAT5e (CAT5) wire due to low cost and easy availability or even scrap. The twisted pairs also help against interference from corrupting the signals. The wiring and concepts in this article apply to CAT5. The suggested wiring for use with CAT5 is below; although you can use any order, just make sure to pick on and stick with it. Crimp with an 6P6C RJ-12 connector, not an RJ-45 network connector.

Pin # Wire Color
1 White / Blue
2 Blue
3 White / Orange
4 Orange
5 White / Green
6 Green

The brown wires are not used and can be clipped off.

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.

The Bottom Line

So what does all of this mean to you and me and our Digitrax Loconet system? We have to make sure that we use a plug/jack that is about 0.375"/0.383" wide and has a 6p6c configuration - ie it takes 6-wires. The only jacks/ plugs/ components that fit the bill are the RJ12 and RJ25.


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. We've got some tips (insert link (content to be developed later) on how you can overcome these limitations).

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® is a trademark of Digitrax Inc.

DCC Systems Employing LocoNet

Digitrax, the owner of LocoNet.

Uhlenbrock Fleischmann

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 MS100 and the third party Locobuffer.

  • 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 adapter work.
    • It has now been discontinued. Its replacement is the PR3.
  • PR3
    • 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.
      • Were 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 adapter work well.
    • Faster serial connection, less/none 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

(need more here)


  • 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


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

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

See Also

See Also - LocoBuffer

See Also - LocoNet