New wine in old bottles!

Linking CANopen to TCP-based networks

Everyone is talking about the Internet of Things (IoT). However, it is, according to CAN in Automation (CiA),  just “new wine in old bottles”. “We do this since more than 10 years,” explained Holger Zeltwanger, CiA’s managing director. “First users came from the ModbusTCP business followed by the generic ASCII protocol.” 

Horst Zeltwanger

CiA had already released the CiA 309 series of interface specification for CANopen-to-TCP gateways in 2004. Recently, the nonprofit association launched new versions for three parts of this set of specifications.

Part 1 (version 2.0) describes the general principles and specifies the communication services. Besides some editorial improvements and corrections, the updated document provides a new section explaining CiA 309 operating sequences. It provides entire protocols, exchanged between a TCP device and a CANopen device, whereby the communication link is established via the CiA 309 gateway device. The CiA 309 services also include management services for the gateway devices and the CANopen host controller. Other services are dedicated to initiate Layer Setting Services (LSS) in order to set the CANopen node-ID via the CAN network or to change the bit-rate. The related CiA 309 protocols are described in part 2 to part 4.

Part 2 released as version 1.3 specifies ModbusTCP messages. The new CiA 309-2 document just introduces some editorial improvements and corrections. Additionally, the Modbus extended exception has been introduced. Part 3 version 2.1 specifying the ASCII-based protocol and launched end of July as the other parts has not been functionally extended. Just a few editorial changes have been made including some additional definitions.

There are some CiA 309 gateways on the market. Most of them use the ASCII-based protocols on the TCP-side. There are also software packages available providing the necessary protocol stacks for both interfaces as well as gateway program. They support ModbusTCP as well as ASCII protocols. In subsea applications, CiA 309 gateways are embedded in the so-called “tree”-controllers, which links the sensor networks on the ocean ground to the topside controller via TCP-based networks.

By means of the CiA 309 protocols, the user can access from a remote controller every device in the connected CANopen network. This TCP-connection is mainly used for remote configuration and remote diagnostic purposes. Real-time communication is done locally. Nevertheless, any CANopen device is via such a standardized CiA 309 compliant interface a “thing” in the Internet.

Additionally, the CiA 309-4 document specifies the remote access via ProfinetIO. CiA and Profibus International members have been jointly developed this specification. Both associations have released it already in the year of 2011.