he CAN in Automation (CiA) international users’ and manufacturers’ group has finalized the framework for TCP-to-CANopen gateways (CiA 309). Part 1 of this set of specifications defines the services on the TCP interface. Part 2 developed jointly with the Modbus-IDA organization specifies the protocols used for Modbus-TCP networks, and Part 3 describes the protocols for ASCII-based commands and responses.
The services and protocols on the CANopen network are defined in CiA 301 (EN 50325-4). The first gateway products based on this framework are already available from several companies.
The services and protocols defined in CiA 309 are used if a TCP-connected controller or tool needs to configure and control any CANopen device in a sub-layered network via a gateway. This includes PDO (process data object), SDO (service data object, and NMT (network management) communication as well as configuring the gateway device.
These standardized gateway functions may be implemented in devices that use CANopen as an open backplane bus. They are also suitable for classic gateway devices connecting a TCP-based network to one or multiple CANopen networks. “More and more applications use TCP-networks as backbone networks for factory automation and CANopen as embedded network for machine control purposes,” says Holger Zeltwanger, CiA Managing Director.
Figure 1: Structure of a TCP-to-CANopen gateway.
Figure 2: ASCII-command and response starting a CANopen device.