Lenz demonstrated the concept at a DCC Working Group meeting in the spring of 2000. It has been incorporated into an NMRA RP for Two-Way communications between the command station and decoders on the track. RailCom is completely backward compatible with Digital Command Control.
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 RailCom Plus
RailCom Plus appeared in 2010
Under DCC, decoders do not communicate with the command station. It sends commands, and the decoder does it. With Railcom decoders can report back to the command station.
- Ops Mode Programming is easier. Ops Mode or Program On Main is supported my many decoders and command stations. Although it is a blind programming method: a CV value changes, but the 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.
- Train number detection: With RailCom compatible detection modules the decoder can transmit their presence in a block along with the [[address], or direction.
Railcom Plus 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.
- A command station compatible with Railcom Plus displays the locomotive, its functions, and saves them for future use.
- If the DCC address are already in use by another decoder in your command station's database, the command station will automatically offer to change the new locomotive’s address to another which is not in use.
To enable the bi-directional features of RailCom some additional components are required:
- A RailCom enabled decoder which can transmit
- Lenz, ESU's Lokpilot and Loksound decoders, and Zimo are among the makers of decoders with RailCom features.
- A detector or reader
- A cutout device that disconnects the DCC signal from the track. This cutout lasts for 488 microSeconds (or 0.488 milliseconds). This break is so brief it doesn't cause problems with the decoders.
- For data transmission to work, the system must interrupt track power between DCC packets. This disconnection period is called 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.
CV28, Bit 0: Channel 1 used for address broadcast. CV28, Bit 1: Channel 2 used for data (CV values, speed, or other data) CV28, Bit 2: Channel 1 used for command acknowledge
The default for CV28 is 3 (bit 0 and bit 1 are set to 1 or high)
What Can RailCom Do?
- Locomotive Identification. When a RailCom equipped 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 decoder: Speed, fuel, water level, etc.
- Data read back: It is possible to display CV values during programming, and acknowledge commands
- Unknown 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.
Railcom uses two channels or slots. Normally a Railcom enabled 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 decoders in the same power district. These transmissions occur at the same time. If the decoders have not been addressed, they won't respond.
By using the Address Broadcast feature, decoders will transmit their addresses, but only using slot one. If multiple decoders are active in slot one, the result is garbage. Any data on the second slot will be readable, being transmitted by a 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 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 decoder, and imports a number of parameters from the decoder, such as address, sound file, function assignments and icons for the functions, without any operator intervention.
The openDCC project supports Railcom via the Open DCC GBM command station. With PC model control software block occupancy and train identification are possible.
Lenz offers the LRC120 address display.
The LRC120 shows 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 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 transmitter module 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.
Lenz DCC Issues
Lenz DCC system software at version 3.6 has RailCom active by default.
If locomotives do not respond, verify the decoder installed. A number of non RailCom decoders offered by other decoder makers do not handle RailCom signals properly and may not work properly with a Lenz DCC system. To solve this issue, RailCom must be disabled in the command station. See the manual for your system.