Term: RailCom

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Summary: RailCom equipped decoders can transmit information back to the DCC System

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RailCom Working Group

LENZ, KUHN, TAMS and ZIMO formed the RailCom Working Group to further develop "bidirectional communication" based on NMRA Draft RP's 9.3.1, 9.3.2.

RailCom® and RailComPlus® are registered trademarks.

RailCom and RailComPlus


Under Digital Command Control, multi-function decoders do not communicate with the command station. The command station sends commands, and the multi-function decoder acts on it. With Railcom multi-function decoders can report back to the command station.

  1. Ops Mode Programming is easier. Ops Mode or Program On Main is supported my many multi-function decoders and command stations. Although it is a blind programming method: a CV value changes, but the multi-function decoder cannot confirm it nor easily read existing CV values. Railcom can transmit CV values without a programming track, as well as provide confirmation of changes to a CV.
  2. Train number detection: With RailCom compatible detection modules the multi-function decoder can transmit their presence in a block along with the [[address], or direction.


RailComPlus appeared in 2010. RailcomPlus is an enhancement of the original Lenz RailCom standard by ESU. Only multi-function decoders which are 100% compatible with the RailComPlus standard can carry the RailComPlus logo.

RailcomPlus is an improvement over Railcom. It allows a locomotive to be automatically recognized and registered by the command station, previously only possible with Märklin's MFX standard for their two rail trains.

The big improvement in RailComPlus was messaging speed. RailcomPlus transmits not only the locomotive's speed, but all the functions available at the same time. This makes the data read function much faster, in addition to new commands to read or write groups of CVs.

  • A command station compatible with RailcomPlus displays the locomotive, its functions, and saves them for future use.
  • If the DCC address is already in use by another multi-function decoder in your command station's database, the command station will automatically offer to change the new locomotive’s address to another address which is not in use.


RailCom Cutout Timing, from NMRA TN-2-05 DRAFT

RailCom Details

To enable the bi-directional features of RailCom some additional components are required:

  • A RailCom enabled decoder
    • Lenz, ESU's Lokpilot and Loksound multi-function decoders, and Zimo are among the makers of multi-function decoders with RailCom features.
  • An external RailCom transmitter
  • A detector or reader
  • A cutout device that disconnects the DCC signal from the track. This cutout lasts for 488 microSeconds (0.488 milliseconds). This break is so brief it doesn't cause problems with multi-function decoders.
    • For data transmission to work, the system must interrupt track power between DCC packets. This disconnection period is called a cutout. The transmission interval is divided into two channels. Each channel can be used independently.
  • During the "cutout" a +/− 30 mA signal consisting of two or four bytes is generated. A current of 10mA is seen as "zero", and a current of less than 6mA is a one.
  • The detector has a very low input impedance (almost a short), any other impedances in the circuit will have little effect on resulting current signal.

Bi-directional communication is enabled in the multi-function decoder with CV29, bit 3. Some multi-function decoders use CV28 to determine the messages that are to be transmitted. The usual configuration of this CV is:

  1. CV28, Bit 0: Channel 1 used for address broadcast.
  2. CV28, Bit 1: Channel 2 used for data (CV values, speed, or other data)
  3. CV28, Bit 2: Channel 1 used for command acknowledge

The default for CV28 is 3 (Bits 0 and 1 are set to 1 or High)

What Can RailCom Do?

  • Locomotive Identification. When a RailCom equipped multi-function decoder enters a section of track with a detector, its presence will be immediately noted. At the same time you'll know where your train is.
  • Info Display: A number of items can be supplied by the multi-function decoder: Speed, fuel, water level, etc.
  • Data read back: It is possible to display CV values during programming, and acknowledge commands
  • Unknown multi-function decoder: If a new locomotive is introduced to the layout, you can find out its address, and even allow a throttle to acquire it automatically.
  • RailComPlus adds the ability to read the multi-function decoder's function capabilities and automatically register the locomotive with the command station.


Immediately prior to the cutout occurring a RailCom compatible command station transmits an Idle Packet. This signals to a RailCom enabled multi-function decoder that the cutout will follow.

RailCom uses two channels or slots. Normally a RailCom enabled multi-function decoder will not transmit during the cutout period, unless it was addressed immediately prior to the cutout occurring. The two channels allow for a response from two multi-function decoders in the same power district. These transmissions occur at the same time. If the multi-function decoders have not been addressed, they won't respond.

By using the Address Broadcast feature, multi-function decoders will transmit their addresses, but only using slot one. If multiple multi-function decoders are active in slot one, the result is garbage. Any data on the second slot will be readable, being transmitted by a multi-function decoder which was addressed. Should an unknown locomotive enter a power district it can transmit its address and register its presence.


Railcom allows a device to interrogate the multi-function decoder and learn some details.

This can be used with block detection, where upon entering a block equipped with a detection system, the detector can report back which locomotive has entered the block.

Some command stations are equipped with Railcom, such as ESU's EcoS system, detect the presence of a Railcom equipped multi-function decoder, and imports a number of parameters from the multi-function decoder, such as address, sound file, function assignments and icons for the functions, without any operator intervention.


RailCom can be used for automation, allowing events to be triggered by a locomotive entering or exiting a zone with a detector. The detector can supply status information to an external computer running appropriate software, which can then trigger various events, such as headlight on/off and sound horn/whistle when entering or leaving a tunnel. Other possibilities include only having passenger trains stop at stations, or selected stations.

Another possibility is using the computer to calculate fuel/water usage, instructing a steam locomotive to halt and take on fuel and/or water. Diesels, which need less fueling can proceed past these facilities. Steam locomotives can also be instructed to stop at an appropriate fuelling location, for oil or coal. In addition to these functions, it could also be used to route a train onto the correct track for passenger or fuel operations. For example, southbound trains are routed to the south platform and northbound to the opposite platform.

This is all possible using the appropriate software and a computer. It will require writing routines or scripts to create and control these actions. The computer will create and transmit instructions to the command station to activate and control various functions in multifunction and accessory decoders as per the scripts.


What is RailComPlus?

What is RailComPlus? Matt Herman from ESU LLC - LokSound explains, and shows us how it works with their new DCC CabControl system.

Standalone Cutout Device for RailCom

Produce or remove a cutout for implementing RailCom on your Model Railway layout

Manufacturer Support

Tams Elektronik

RailCom Devices


The openDCC project supports Railcom via the Open DCC GBM command station. With PC model control software block occupancy and train identification are possible.



ESU offers the 54680 RailCom transmitter. This transmitter, installed in a vehicle with a multifunction decoder which does not support RailCom, adds full RailCom compatibility. There is no need to upgrade the existing multifunction decoder. It is programmed to match the address of the vehicle and will respond to a RailCom receiver.

These devices only work with specified ESU command stations and boosters.



The LRC100 is a small module which allows locomotives equipped with a multifunction decoder (without RailCom) to be retrofitted for RailCom.

LRC 120

Lenz offers the LRC120 address display.

The LRC120 displays the address of a locomotive in a track section connected to the LRC120. This track section may be located at any point on your layout.

For the LRC120 to display the address, a RailCom capable booster must be used, such as Digital plus LZV100 or LV102, which currently have this feature. These units are equipped with the necessary cutout device.

When the LRC-120 is active the first digit of the display displays a - . When a locomotive equipped with a RailCom enters the section monitored by the LRC120, the address of the locomotive will be shown on the four-digit display.

If the locomotive is a member of a consist, the consist's address will be displayed. Thus, the display always shows the address which you can use to control the speed and direction of the locomotive from your throttle.

The LRC120 is also capable (in the future) of displaying CVs.


Most issues are related to the command station and multifunction decoders.

Many, but not all, command stations generate a preamble with more than the minimum number of 12 bits. The extra preamble bits can be used for the RailCom cutout. Problems arise with multifunction decoders expecting 12 or more preamble bits. Many multifunction decoders will function with only 10 preamble bits. Should the command station generate 16 preamble bits, 4 can be used for the RailCom cutout, without out impairing decoder operation.

Lenz DCC Issues

Lenz DCC system software Version 3.6 has RailCom active by default.

If locomotives do not respond, verify the multi-function decoder installed. A number of non RailCom capable multi-function decoders offered do not handle RailCom signals properly and may not work with a Lenz DCC system. To solve this issue, RailCom must be disabled in the command station. See the manual for your system.

Lenz command stations and boosters accurately implement the NMRA DCC standards, often any problems encountered are related to multi-function decoders which do not correctly follow the DCC Standard.

TCS WowSound Multifunction Decoders

TCS WowSound multifunction decoders may not function correctly if RailCom is active. This is usually related to having a European command station, such as those from Lenz or ESU. Disabling the RailCom features should eliminate the issue.

Some TCS multifunction decoders do support RailCom. Firmware Version 89 and higher support RailCom and RailComPlus, provided they are purchased directly from TCS. Vendor stock may be a lower firmware version and results may vary.

NCE Multifunction Decoders

Due to the design of NCE's multifunction decoders, they do not correctly follow the NMRA DCC standard. The solutions are to disable RailCom at the booster or replace the decoder.

Accessory Decoders

Some accessory decoders, if receiving instructions via the DCC Power Bus, may not work well with RailCom.

Further Reading


  1. NMRA
    1. Communications Standard for Digital Command Control Basic Decoder Transmission
    2. TN-2-05 DRAFT
  2. Lenz website, in German. Unfortunately, Lenz no longer maintains a presence in North America.
  3. ESU RailComPlus FAQ
  4. locgeek.com Railcom-Railcom-Plus-What-are-These?
  5. RailCom Uses
  6. DCC4PC Railcom products
  7. www.lenz.com: This website is no longer active.

JMRI also supports RailCom.