Powerlink - Cycle, Time Slot Principle - TR-Electronic 65 Serie Gesamt-Bedienungsanleitung

POWERLINK Information
3.1.3 POWERLINK – Cycle, Time slot principle
POWERLINK is based on standard Ethernet with CSMA/CD technique which is
afflicted with collisions, but with the time slot method this problem will be avoided. In a
POWERLINK network only one node may send at the same time, thus POWERLINK
is also applicable for hard real time requirements.
Network access is managed by a master, the EPL Managing Node (MN). A node can
only be granted the right to send data on the network via the MN. Further the MN
synchronizes all connected nodes. The remaining nodes, Controlled Nodes (CN),
react to its instruction. Figure 2 shows a complete EPL communication cycle.
Figure 2: EPL Cycle diagram
Communication is effected with the time slot principle mentioned already above. Each
configured CN is accessed cyclically by the MN. At the beginning of an EPL cycle, the
MN is sending a "Start of Cycle" frame to all nodes via Ethernet multicast, which is
used by the CNs for synchronization purposes. After that the MN sends a "Poll
Request" to the first node, which then transmits the received data to the outputs (I1)
and records new process data. After a predefined time all configured CNs are
accessed by the MN. For this purpose the MN sends further PReqs to the nodes. The
PReq contains output data for the node and serves as transmission request.
If a configured CN receives the PReq, he saves the input data and sends a "Poll
Response" with the data recorded with the SoC as broadcast (I1...In). Thus it is
possible for all other CNs, "to monitor" these transmitted data. Cyclical communication
is terminated by an "End of Cycle" frame. After that there is an asynchronous period
while user-defined communication can be performed and is initiated by a "Start of
Asynchronous" frame.
SoC:
PRes (MN):
PReq:
PRes:
SoA:
ASnd:
MN:
CN:
Ix:
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Start of Cycle
Poll Response Managing Node --> End of Cycle
Poll Request
Poll Response
Start of Asynchronous
Asynchronous Send
Managing Node
Controlled Node
Isochronous data, Process data
TR - ECE - BA - DGB - 0071 - 05
Printed in the Federal Republic of Germany
06/26/2017