Firmware Copyright

Copyright© MERG and Rocrail.
Commercial use is prohibited.

A RFID mergCBUS reader concentrator based on RFID-12.

Preferred is the ID-12LA reader because it is much faster then the ID-12 and ID-20.


The final version with an extra MERG CBUS 12V connector.


  • 8 channel RFID reader input using the same type as MERG RFID12.
  • Connector for the GCA93 8 port current detector.


  • The displacement between RFID readers, ID-12LA, should be at least 30cm to be able to function.
  • The distance between reader and transponder is for small types critical; Create a test environment to test it to find out the best placement.
  • See for more information: Bi-Directional Communication.


Merg did a fine job in combining 8 RFID sensors attached to one board and from there read all sensors and send a completed number over the serial port to a PC.
This board is stepping a bit further by doing the same thing and in addition has CBUS on board so the separate RS232 port is no longer needed.
The received numbers are simply send via the CBUS.

Allthought Rocrail can handle also the MERG RFID concentrator, connected to a serial or USB port, this CAN-GC4 is a bit more easy to connect.
To power all connectable 8 RFID sensors, the board needs a power supply of approx 0.25Amp at 5V.
For a linear regulator 5Volt , this is way too much for continuing functioning.
The CAN-GC4 steps down the 12 Volt as available in the CBUS network.

LEDs & Connectors



LED# Function Aspect Remark
1 CBUS activity random flashing Depends on CAN traffic
2 Run continuos The board does not function if this LED does not illuminate
3 Learning mode 500ms blinking Activated by push button or Rocrail setup.
3 RFID checksum error or the ID is not in the list of allowed RFIDs. One shot flash


Name Function
Rf1-Rf8 RFID readers.
J4 Optional for current detection GCA93.
ICSP1 PIC Programmer.
J3 MERG CBUS with 12V connection.
J1 CAN-GC connector out
J2 CAN-GC connector in

PSK header connectors




RFID Column

The 8 ID-12LA readers can be assigned an address used for CBUS events.¹

BK Column

The 8 block occupation detectors, GCA93, can be assigned an address used for CBUS events.¹

Allowed RFID Column

Used in combination with the Check RFIDs option for generating only events for IDs set in this list.
Starting with revision 3458 the RFIDs must be set in dot-decimal notation.
“5555” would be “”. The easiest way is to copy the dotted RFIDs from the Rocrail server trace.


Save RFIDs

Used for SoD; Use with care → Old information is reported!

Check RFIDs

The incoming RFID must be in the list of allowed RFIDs for generating a CBUS event.

Release RFIDs

An event with OPC_ASOF is send after 2 seconds to release the related sensor.

Accessory events instead of RFID events!!!

:!: No RFID event is generated if this option is active!

For use in combination with check RFIDs to trigger an output on the CAN-GC2.

¹) In Rocrail this is the sensor address.

RFID Notation

The RFID(Identifier) is formatted as dot-decimal notation with 5 parts:

Dot-Decimal Hexadecimal Decimal 0xFFFFFFFFFF 1099511627775

Rocrail server trace with activated monitor level:

20120328.181017.123 r9999c cbreader OCBUS    0889 RFID short event 107 id=

See also: Loco Identifier

Sensor Type

The sensor type used for the RFIDs in CBUS is “5 RFID”. (3472+)

RFID Readers


The ID-12LA is much faster with scanning compared with the ID-12/ID-20.



This unit has extended possibilties, compared with the RFID concentrator s available from MERG.
Non of the recommended RFID readers and tags can be ordered from GCA.

Mounting Tags


This is an example of how to mount a 12mm 125kHz RFID ID Tag under the fuel tank of a Brawa 61200 “V160” diesel locomotive:
A small axial round groove is grind between the two tanks to make place for the Tag. Some details are destroyed but thats not visible at normal operation.
The Tag is fixed with some transparent adhesive.

RFID Hotspot

The red LED illuminates if the reader detects a RFID Tag.
Only Tags on this track are detected; Tags traveling by on the other track are out of reach.
The plywood is cut out from underneath, leaving 1 mm on top, so the reader is mounted only 1 mm rom the bottom of the track.
The distance between sensor and transponder is approx 10mm.


Even a small H0e mining kipper can be detected!
No way to get a RailCom decoder in this one. :-)

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