CAN-GC1 RS232/USB CANBUS Interface with 3 Amp Power supply


Copyright Peter Giling

MERG has been succesfully developing and using the CAN network for modelrailroad.
The basic idea to follow the trend in GCA (MGV) boards and to have this CAN network adaptable for all available interfaces, like GCA93, GCA136, GCA76 and many others.
The standard MERG units are all made ( so far ) for 8 bytes only, and also different tasks like input, current detection, turnout coils, etc, need different units to connect them .
Most mergCBUS units in this line will have 16 bits on board, and each of these bits ( = ports) is programmable for any task you want.
Rocrail supports this way of programming with extending possibilities, making the whole process of configuration exactly the way it should: user friendly !

The pcboard

A professional produced board with through metallisation, soldermask on both sides and clear print is available now.
Connectors also have 12Volt to feed all connecting nodes.
The basic idea is to use this type of board for modules setup, which are frequently disconnected and transported.
These modules can be placed together in different order.
MergCBUS is ideal for that!
The users I have to deal with, like a better connector, instead of fastening wires in screw-terminals.
Therefore I use the easy to assemble and rigid D-connectors.
All interfaces, used for turnouts and other current consuming peripherals, as available from
LocoNet interfaces are fully compatible and isolated from the mergCBUS system by opto-couplers,
MergCBUS connectors only have to supply mergCBUS system itself, so Subd9 connectors are very well suitable.
All CAN-gcx boards have on-board jumper to connect 120 Ohm to the mergCBUS, of which one should be at each end of the Bus.
Please consider, that it is not allowed to connect- or disconnect the mergCBUS , while in function.
This is a general recommandation for CAN.

The hardware



www.ftdichip.com_images_db9-usb-rs232_web.jpg The picture above shows the board with fitted D-Sub-USB connector. (Its a bit more expensive but the best solution.)
A more 'value for money' solution is to mount standard D-Sub connector and use an USB-RS232 conversion cable.

:!: Most RS232 legacy ports cannot handle baud rates above 115200.
A USB converter is highly recommended.

Hardware for CAN-GC1

Boards, programmed processors and complete kits are available from
With a proper tool, it is possible to do the programming of the chip yourself.
The programmer , used for these chips is called PICKIT 3 from Microchip.
The on-board ICSP connector is useable for this programmer.
ICSP connector on-board is made conform specification of MERG.
For connection to PICKIT3, the cable cannot be 1 to 1.
See PICKADAP4 how this is done.


CAN-GC1 is based on MERG CANRS and therefore is the setup fort both connector 1 types, RS232 and FTDI-USB, the same:

Sub-Library Serial Do not select USB type for the FTDI-USB connector!
BPS 230400

Windows Driver for FDTI (USB)

LEDs & Buttons


LED Usage Remark
Le1 Bus activity It is not timed and thus only visible at high CBUS traffic.
Le2 CPU runs
Le3 Not used; Leave unmounted. For future firmware versions.
PB1 Not used; Leave unmounted. For future firmware versions.

Power supply

On J1 a power supply of 12-20 V AC OR 16-24VDC can be connected.
For DC supplies: Polarity is irrelevant.

Connecting CAN-GC1


  1. USB or RS232 Sub-D 9 connection.
    In case of USB: Make sure the plug is completely in the socket; It needs a little force the first time.
  2. Jumper for 120 Ohm line termination
  3. CAN Bus with 12V power
  4. CAN Bus with 12V power
  5. Power input 16…24V AC/DC
  6. PIC Programmer

Compatibility with mergCBUS

The reason for using D-type connectors has been explained before.
Electrically , there is no difference between mergCBUS (12V) and CAN-GC .
The following conversion tabel explains how both can be interconnected.
Only four wires are needed.
Use the standard wiring as advised in MERG documentation, i.e. twisted wires for the CAN.

mergCBUS side SUB-D connector pin#
CAN-H pin 8
CAN-L pin 7
+ 12V pin 5
GND pin 1

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