The CAN (Controller Area Network) protocol was originally developed for the European automotive industry, so as to replace expensive cabling by an affordable network cable. Today, it is also used in the field of automation for transmitting process data between control systems, decentralized I/O modules, drives, valves, etc. CAN features a high level of transmission security, since large portions of the monitoring mechanisms have been implemented directly in the CAN chip. DeviceNet and CANopen utilize the physical structure and the data transport mechanisms of CAN (Controller Area Network). The difference lies in the transmission protocols. DeviceNet and CANopen can be used correspondingly for the AC500 and AC31 controller series and for field-bus-neutral FBP devices (decentralized I/Os and intelligent switching devices), via the CANopen-FBP plug connector.
Data transmission
Two types of message have been defined: I/O data transfer and direct link. I/O data transfer is used for time-critical process data, while the direct link can be, for example, used for diagnostic messages.
Bus access for subscribers
The connection ID with the lower address has higher priority on the bus. Data is transmitted by the source, while the sinks (i.e. receivers of the data) have likewise been specified during the configuration phase.
DeviceNet
The bus operates on the multi-master and/or the master/slave principle, with up to 64 bus subscribers. Two types of shielded twisted-pair cables are used: trunk cable for the main line and drop cable for the branch line.
Diagnostics
Detailed diagnostic messages for rapid troubleshooting are shown on the CPU display. In addition, the device status is indicated at the communication module by four LEDs.