Introduction Ethernet POWERLINK
Ethernet POWERLINK is a Real-Time Ethernet field bus system. It is based on the Fast Ethernet Standard IEEE 802.3.
A managing node (MN), which acts as the master in the EPL network, polls the controlled nodes (CN) cyclically. This process takes place in the isochronous phase of the EPL cycle. Immediately after the isochronous phase follows an asynchronous phase for communication which is not time-critical, e.g. TCP/IP communication. The isochronous phase starts with a cyclic frame on which all nodes are synchronized. This schedule design avoids collisions, which are usually present on Standard Ethernet, and ensures the determinism of the hard real-time communication. It is implemented in the EPL data link layer. The EPL network can be connected via gateways to non real-time networks.
The communication profile of Ethernet POWERLINK is adapted from CANopen. Thus the design principles like process data object (PDO) for exchange of process variables and service data object (SDO) for configuration of remote object dictionaries are reused. All PDOs are exchanged within the isochronous phase similar to the synchronous PDOs of CANopen, because event triggered PDOs would interfere with the hard real-time requirements.
To conform to IEEE 802.3 each EPL device has got a unique MAC address. Additionally each device is assigned a logical node ID. Mostly, this node ID can be configured via node switches on the device. If a particular EPL device implements a TCP/IP stack it gets a private IP address from class C within the network 192.168.100.0 where the host part equals the EPL node ID.
It is assumed that you are familiar with the Ethernet POWERLINK V2.0 Communication Profile Specification.