CAN-GC2G Multi functional I/O node for CANBUS

Firmware Copyright

Copyright© MERG and Rocrail.
Commercial use is prohibited.

The CAN-GC2G is an alternative to the CAN-GC2 with integrated drivers, useable as a complet unit without
extra drivers, running on the mergCBUS open source CAN standard.
This unit enables direct connection of the following peropheral:

  • 2 x Turnout output for single coil units.
  • 8 x Low impedance input for Hall sensors or reed contact
  • 3 or more free configurable I/O ports
  • High current switch for reverse loop control

The pcboard


A jumper makes it possible to set terminator on the last board in the mergCBUS chain.
This jumper connects a 120 Ohm resistor to the Merg CBUS.
The base for creation this board is to make use of CBUS easier for garden railroad.
It does basically not need anything else to control 2 turnouts with single 24V coil
Any other voltage up to 24V dc is possible.
Further more 8 inputs are pre conditioned for use with Hall sensor or reed contact,
and addionally there is place and control for two relays with 10Amp contacts to be able to reverse the rail power inside a reverse loop.
These relays will be controlled by Rocrail, direct control via reed contact or Hall sensor is also optional.
Power, as available in Merg CBUS-cable, is only used for supply of mergCBUS board itself.
The reverse loop relays and the outputs for turnout need 24 V by standard.
Adaption to lower voltage needs different 10Amp relays.
As a standard recommandation for all CAN systems, connection and disconnection of cables is not possible while system is running.
Cable connection is done in the same way as standard with Merg CBUS, by screw terminals
Extra supply connection for 24V is also available.
Specially for outside use in humid weather conditions a heating resistor is also situated at the back side of the board.
A few degrees warmer inside the box, compared to outside conditions, will do miracles for the board.
However is advisable to be sure the box where this board is placed, is very seriously closed and IP66 waterproof.

The schematic

The principle of this board is equal to CAN-GC2. It uses the same firmware.
IC1 is main processor, taking care for all ports.
IC2 is the CAN driver, that takes care for correct handling of the CBUS.
IC3 is the same processor as used on GCA173 and GCA179, with almost the same firmware.
IN1.. In8 connections can be used for Hall sensors or reed contacts.
The impedance is speciall kept as low as 470 Ohm , to suppress distorsion on longer (<3m) lines.
The fimware in IC3 will make sure that also short pulses specially with reed contacts,
create a solid contact info to IC1.
Ports 9..12 have a double function.
Initially they are connected to the outputs of IC3 for IN5..In8.
But is also possible to use them as output ports.
To avoid conflicts between IC1 and IC3, when both are cionfigured as output, resistors R12.. R15 will
protect these ports. When port is configured as output, IC3 will not have any incfluence on that port.
Turnout 1 and 2 are switched by relays K1..K4.
The type of the motors of these turnouts are of single coil type.
Combination of relay 1 & 2 , -or 3 & 4-, will switch +/- or -/+ depending on desired direction of turnout.
Pulse length can be programmed as with CAN-GC2.
VDR1 and VDR2 are very important, and will suppress inductive fly-back from the turnout coil, to avoid distorsion into th total system.

Reverse loop switch can be used to reverse the rail power in a loop, when needed.
Always 1 of two relays will be switched ON.
Rocrail can be programmed in routes (commands) to set the correct polarisation.
It is also possible to use two inputs IN7 & IN8 to set these polarisation with reed contacts or hall sensors.
This is specially nice if you want to control you trains manually,
and do not have to worry about correct polarisation by entering or leaving the reverse loop.
These feature needs different firmware for IC3.
If you are intersted in that option, ask Peter.

The hardware

The schematics
The pcboard and parts positions
The partslist
Gerber files
N.B. Only complete ordered kits will be supported!


CanBus is a 4 wire cable, where both CAN+ and CAN- lines shopuld be twisted all over the full length.
The best cable for that purpose is a a widely available CAT5 cable.
Shield is Ok but for up to 200 mtrs not needed.
Connections on CAN-GC2G and CAN-GC1e are identical
Two more terminals, indicated as POWER2, are for the 24V dc to be used for turnouts and reverse loop relays.
This 24 V can be feeded over the same CAT5 cable with a twisted pair. Ground of Power 1 and power 2 should be linked.
This means that , unkless special precaution is made on CAN-GC1e, it is NOT possible
to supply CAN-GC1e and power 2 with the same power supply.

Configuration of ports

Though the firmware of this CAN-GC2G is equal to CAN-GC2, it has a number of pre-defined ports.
Adresses for turnouts should be in following order

Port # Function Input/Output pulse/switch Connection Remarks
1 Turnout 1a output Pulse Turnout 1
2 Turnout 1b output Pulse Turnout 1
3 Turnout 2a output Pulse Turnout 2
4 Turnout 2b output Pulse Turnout 2
5 Sensor 1 input/block x IN1
6 Sensor 2 input/block x IN2
7 Sensor 3 input/block x IN3
8 Sensor 4 input/block x IN4
9 Sensor 5 input/block x IN5 also as free I/O at J3 pin3
10 Sensor 6 input/block x IN6 also as free I/O at J3 pin4
11 Sensor 7 input/block x IN7 also as free I/O at J3 pin5
12 Sensor 8 input/block x IN8 also as free I/O at J3 pin6
13 Free I/O input/output free J3 pin 7
14 Free I/O input/output free J3 pin 8
15 Free I/O input/output free J3 pin 9
16 reverse loop switch output switch* Reverse loop
or J3 pin 10
If relays K5 and K6 are not installed,
port 16 is open like Port 15.

* Port 16 should be programmed as single output for use with reverse loop.

Led functions

L1* L2 L3*
Can bus activity Programming activated Unit running

* leds are blinking

PB1 functions

PB1 Function
After power on Switch to learn mode for setting a node number.
A second push will leave this mode.

Connector J3 10pin header

LocoIO port Pin #
+5V 1
9 3
10 4
11 5
12 6
13 7
14 8
15 9
16 10

Direct connection of leds to outputs

Reed switches and hall sensors

Read switches and hall sensors can be used as feed-back sensors.
They will be connected to IN1 to IN8, which numbers correspondent to I/O Port 5.. I/O Port 12.
Reed contacs are connected to point - & s on each connector.
The CAN-GC2G provides an extra processor, to be able to time all -even very short- pulses from reed-contact
to a reasonable longer pulse, to enable the CAN processor to read this info correctly.
Input impedance is kept low, to limit distorsions on longer lines (Max 3 meters) form the sensors.



Hold down the button at power on to reset/initialize the EEPROM with following settings:

  • port 1-8 switch with address 1-8
  • port 9-16 block with address 9-16

The same can be achieved by sending a Clear command.


Set the first found change. This button must be pushed multiple if more then one port or setting is changed.
The sequence of change check is:

  1. Ports
  2. Node configuration
  3. SoD

Set all

Set all ports and options.

Save output state

Write the output state in EEPROM after detecting a power off command on the mergCBUS.
The outputs will be restored after the CAN-GC2G is powered on.

Short events

Ignore the event node number and compare the event number only.

Long events

For long events the BUS variable on the interface tab of sensors, switches and other objects is used to address the module its node number.
The address variable is equal to the one used with short events.


“Start of Day”
The CAN-GC2 will report the status of every input after receiving an accessory command with this address. (Short event)
The SoD address should be the same as set for the Controller and can be tested with the SoD button.

Node Nr.

For outputs with long events only.
Inputs will use the CAN-GC2 node number for events.

Port types

Type Description Recommendation
IN Input Normal input port. Push buttons, feedback of servos/points and hall sensors.
BK Block Input with a 2 seconds delayed off. (±50ms) Occupancy detectors.
SW Switch Continuous output. Single coil switch drivers like servos.
PU Pulse Output with x ms activation time. (±50ms) Note: A software timed off is not possible with mergCBUS; It is realized in the hardware.

Pulse time

Activation time for pulse type outputs.


Inverts the port.


Every port has a test button in which also the current state is displayed as a “1” or “0”.
The state is only updated after pushing a test button.


Shows the Rocrail object ID which is linked to this port.

Node Variables

NV# Purpose
1 General configuration
2…17 Port configuration

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