Support: Digitrax LocoNet®

Supported Hardware

JMRI software, including DecoderPro and PanelPro, works with your Digitrax command station to program decoders. To do this, it communicates with the command station over the LocoNet® using one of several types of adapter.

Command Stations

JMRI software supports the following LocoNet-based command stations:

For systems which do not provide a LocoNet command station, two additional options are supported. When a layout uses LocoNet peripheral devices but not a LocoNet-based command station, a "Standalone" LocoNet is used. See Standalone LocoNet. In addition, JMRI software may be configured to use a simulated LocoNet connection instead of a real LocoNet connection. This is the "LocoNet Simulator".

Computer Interfaces

To connect your computer to the LocoNet, and hence to the command station, you need one of the following adapters:

(Note: The Digitrax DSC240 has a built-in adapter that's similar to the Digitrax PR3; if you have a DCS240, configure JMRI for it by selecting a PR3 connection type and a DCS240 command station type)

Generally, any of these can be used with any type of computer to communicate with any type of command station. Currently, the LocoBuffer-USB and PR3 are the recommended computer interface solutions. The LocoBuffer II and original LocoBuffer are no longer commercially available; their primary advantage now is that they use a traditional serial port, which may be the only suitable connection type available on some older computers.

The MS100 is not recommended; it sometimes fails to provide reliable communications, and it cannot be used with JMRI if you are using Mac OS X or on most Windows Vista machines. If you have problems with the MS100, you might not be able to fix them, and nobody may be able to help you.

The Uhlenbrock Intellibox command stations can also be controlled directly through it's serial port or USB connection; there's a separate page on how to do this.

PR2, PR3, and PR4 Programmers

JMRI can also use a Digitrax PR2, the Digitrax PR3, or the Digitrax PR4 to program and test decoders. The PR2 is a stand-alone decoder programming unit which does not connect to the rest of the layout, the command station, nor to a LocoNet. For more information on using a PR2 with DecoderPro, please see the PR2 setup page. The PR3 and PR4 devices can be configured in JMRI to operate as either a stand- alone programmer, or as an interface to to a LocoNet. There is more information on the PR3 setup page and the PR4 setup page.


Uhlenbrock Intellibox - The Intellibox has two LocoNet connections, called LocoNet-T and LocoNet-B. The LocoNet-T connection can drive more devices, but does not provide the Rail-Synch signals that some LocoNet devices (particularly boosters and the BDL16, BDL162 and BDL168) require. A LocoBuffer should be connected to the LocoNet-T connection.

Uhlenbrock Intellibox II and IB-Com - The Intellibox II and IB-Com have two LocoNet connections, called LocoNet-T and LocoNet-B. The LocoNet-T connection can drive more devices, but does not provide the Rail-Synch signals that some LocoNet devices (particularly boosters and the BDL16, BDL162 and BDL168) require. A LocoBuffer should be connected to the LocoNet-T connection.

PR-1 not supported - Note that DecoderPro cannot directly program decoders via a PR1 programmer. JMRI supports decoder programming either via the PR3 as a stand-alone programmer or via a command station.

Mac OS X and the MS100 - Because Mac OS X can't communicate at the special baud rate used by the MS100, the MS100 won't work with Mac OS X. You should get a LocoBuffer-USB instead.

Microsoft Vista and the MS100 - It has been reported that Vista does not support the special baud rate used by the MS100. If you find that your MS100 does not work on your Vista machine you should get a LocoBuffer-USB or PR3 instead.


To connect your computer to a Digitrax DCC system, you need a LocoBuffer-USB, PR3, LocoBuffer-II, LocoBuffer or MS100 to act as an adapter. See below for more information on these. The LocoBuffer-USB is highly recommended.

Note that except for the PR3, these are only LocoNet interfaces, not stand alone programmers like the Digitrax PR2 and PR3. Readback of decoder CVs is possible when using a programming track controlled by a PR3 (in stand-alone programming mode) or a programming track controlled by a Chief or Zephyr command station. The Empire Builder command station does not allow Readback of decoder CVs; users of the Empire Builder can add CV Readback capability by using a programming track connected to a PR3 operating in stand-alone programming mode.

The steps below show how to add a connection to JMRI (DecoderPro, PanelPro, etc.) for a LocoNet-based system.

  1. Connect your adapter to the LocoNet, and connect your computer to it with the appropriate serial or USB cable.
  2. Mac and Windows users should install the proper USB drivers if they are using USB devices.
  3. Linux and Mac users should be sure that the correct Java communications packages have been installed.
  4. Open a JMRI program and go to the "Preferences" panel. This normally opens automatically the first time each program is run, or you can select it from the "Edit" menu.
  5. Select the "Connections" item in the window at the left.
  6. Select "Digitrax" in the "System Manufacturer" box.
  7. Select the appropriate adapter type in the "System Connection" box.
  8. You can then configure the proper settings in the "Settings" box. The "Serial Port" must be properly selected and the connection settings properly configured in order for JMRI to talk to the adapter hardware. On some systems with some system connection adapter types, the "Serial Port" setting will be automatically selected. In other cases the first possible "Serial Port" connection will be selected by default. It may be necessary to use tools provided with the computer operating system to determine which "Serial Port" is appropriate for your particular situation.
  9. Select the appropriate "Command Station Type":

    When the "Connection Type" is set for the PR3, the "Command Station Type" can be set to "PR3 in stand-alone programming mode" or set to one of the command station types. When set for stand-alone programming, the PR3 will not communicate with LocoNet. When set for a specific command station type, the PR3 programming track is not used; instead, decoder programming is done through the mechanisms provided by the selected command station.

    When "DB150 (Empire Builder)" is selected, JMRI decoder programming is done via the DB150 programming mechanisms. The DB150 is not capable of reading decoder CV values, so JMRI will not be able to read decoder CV values via the DB150 programming mechanisms. Empire Builder users can use a PR3 in stand-alone programmer mode, instead of the Empire Builder programming track, to allow decoder CV readback. Some users configure DecoderPro for programming decoders using the PR3 in stand-alone programming mode, and then configure PanelPro to use the PR3 in LocoNet interface mode (also called "MS100 mode") to allow PanelPro to communicate with the Empire Builder command station and LocoNet-connected peripherals. More PR3 setup information can be found on the PR3 setup page.

  10. The "Connection Prefix" is used to help JMRI communicate separately with multiple "connections" to layout hardware. Each "connection" must have a unique identifier, which is specified as the "Connection Prefix". By default, the first LocoNet connection is given a prefix of "L", and additional LocoNet are given prefixes like "L1", "L2", ... Most users should be able to use the default "Connection Prefix" value provided by the JMRI tools.

    It is recommended that all connections for LocoNet hardware use a prefix that begins with "L", as other characters are normally associated with other hardware connection types.

  11. When a JMRI tool is configured for more than one connection, each connection gets a menu item on the main JMRI tool window. To help users differentiate between their different connections, each connection has a "Connection Name", which is used as the name of the associated menu item on the main JMRI tool window. Users may change the "Connection Name" for any connection to suit their needs.
  12. Some adapters may have addition configuration options, which may be shown by checking the "Additional Connection Settings". This may show additional settings which may be made for some adapter types. These include, but are not limited to, the options listed here.
    • The "Baud Rate" setting. When multiple settings are available, this must be set to match the needs of the particular hardware adapter specified in the "System Connection" setting. This setting will be pre-set and unchangeable you have selected a LocoBuffer-USB, PR3, or MS100 "System Connection". There are two speed choices for the LocoBuffer and LocoBuffer-II; select the one that corresponds to the jumper settings on your LocoBuffer unit. We recommend that you start with the 19,200 choice for the LocoBuffer or LocoBuffer-II; see the LocoBuffer-II and LocoBuffer pages for more information.
    • The "Command Station Turnout Command Rejection and JMRI Turnout Command Handling" setting is described below.
    • The "Connection Uses" selection determines how "flow control" is implemented in software. This selection should be configured for "hardware flow control" unless you later consistently get a JMRI console message about the LocoBuffer control leads being improperly set up, in which case you might want to try to bypass that by selecting "no flow control". This box will be blank if you've selected LocoBuffer-USB, PR3 or MS100.
  13. Click "Save". You'll be asked if it's OK for the program to quit, click "Yes".
  14. Restart JMRI. You should be up and running.

If you are going to control Turnouts, Signals or other devices on your layout from JMRI or another program, we recommend that you set the command station's "Meter route/switch output when not in trinary" option "Off" (Thrown). When On, this option greatly reduces the number of commands the LocoNet can handle each second, which can cause significant delays when you're controlling signals, etc. To turn it off, you can use the "Configure Command Station" tool in the LocoNet menu to set Option Switch 31 to "T" (Thrown), or set it via the Roster-based mechanism, or set it directly in the command station using a Digitrax Throttle.

If you will have multiple connections, the "Defaults" tab in the "Preferences" panel may be used to direct certain types of operations to different connections. A good example of this is a system with two PR3 connections, one in stand-alone programmer mode for programming decoder CVs, and the other for communication with a layout LocoNet and command station. In this case, use the "Defaults" settings to select one LocoNet connection only for "Programmer" and the other LocoNet connection for "Throttles", "Power Control", and "Command Station".

Using JMRI with LocoNet®

JMRI provides a number of features which allow it to interact with LocoNet.

Networked Computers and LocoNet®

There are several mechanisms available to allow multiple computers to communicate with LocoNet. These communicate via standard TCP/IP protocols, and can even work remotely. At least one of the networked computers must have a functioning LocoNet interface. See this page for more information.


Erratic or Non-Functioning CV Readback

Command Station Turnout Command Rejection and JMRI Turnout Command Handling

Digitrax command stations pass LocoNet switch command messages to the DCC track signal so that track-connected accessory decoders can receive the switch commands. Digitrax command stations seem to buffer the switch requests and forward them to the DCC track signal in a way that does not have a noticeable impact on mobile decoder response to throttle control operations. This buffer is limited, and under conditions of heavy LocoNet switch command traffic, can overflow. When this happens, the command station will respond with a message (a \<LONG_ACK\> opcode) saying that it rejected (did not accept) the switch command. When the command station gives this response, the switch command is not placed into the buffer and is forgotten.
This can be problematic, depending on how the device which sent the switch command responds to the rejection message on LocoNet. Many LocoNet devices do not notice the rejection message, so do not attempt to re-send the switch command. Other LocoNet devices can pay attention to the rejection message and can wait a while before re-sending the message. Some LocoNet devices can be programmed either to resend the switch command if the rejection message is seen, or to not resend if the rejection message is seen.
This wide variety of behaviors can cause inconsistent or unreliable behavior of any device which relies on stationary decoder messages on the DCC track signal. Note that this can include devices which connect to LocoNet and which monitor the DCC track signal which is available on the LocoNet cable "RailSync" wires.



JMRI provides specific support for the a variety of Digitrax and 3rd-party LocoNet-based hardware, as well as a variety of tools to configure LocoNet hardware.
Some links:

Third Party/Support

Support for Digitrax hardware products is available through Digitrax, Inc. Digitrax product manuals may be found here. Note that Digitrax does not provide support for JMRI software.

Many knowledgeable Digitrax users contribute to the Digitrax users Yahoo group. If you have a problem with Digitrax equipment, this is a good place to pose your Digitrax-specific problems. This user's group is run by and for Digitrax users. It is not directly supported by Digitrax.

For JMRI-specific questions, including questions about how JMRI and Digitrax hardware interact, the JMRI users Yahoo group is very helpful.

LocoNet® is a registered trademark of Digitrax, Inc.