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CIPsync will boost real-time performance of DeviceNet

01 May, 2003

CIPsync will boost real-time performance of DeviceNet

The ODVA (Open DeviceNet Vendors Association) is adopting the IEEE 1588 time synchronisation standard for its Common Industrial Protocol (CIP). CIP is the underlying protocol for both DeviceNet and EtherNet/IP. The synchronised CIP will be designated CIPsync.

The IEEE 1588 standard, known as "Precision Clock Synchronisation Protocol for Networked Measurement and Control Systems," is designed for local area networks such as Ethernet UDP/IP that support multicast messaging. Every second, the main controller broadcasts a synchronisation signal to all nodes on the network. For a 100Mb Ethernet system, this will allow hundreds of nodes to be synchronised to within tens of microseconds. In future, special "accelerate" circuits could be added to Ethernet chips, boosting the timing performance to 500 nanoseconds.

CIPsync does not in itself bring real-time performance to automation systems, but it can help schedule and co-ordinate events to more precise time intervals to achieve real-time action.

For example, in a complex machine with many servo motors, a command could be transmitted to perform a specific co-ordinated action at a specific time. Even though the command may arrive at the different nodes at different times, because the nodes are precisely synchronised with a master time clock, they will carry out the command at a precise time.

"CIPsync takes the requirement for determinism out of the network and puts it in the end node," explains Paul Brooks of Rockwell Automation. As long as the command signals are not too frequent — he says one each millisecond is about the maximum — the entire system can perform actions co-ordinated to within microseconds.

CIPsync will be implemented first in EtherNet/IP. Work on a DeviceNet version is due to start next year.

One of the first applications of the IEEE 1588 technology will be in Ethernet supervisory networks in power stations where the actions of various nodes, such as circuit breakers, need to be recorded with high accuracy to determine the cause of a power interruption.

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