Communication
41
Communication
What this chapter contains
This chapter describes the communication on an Ethernet
POWERLINK network.
Ethernet POWERLINK communication cycle
In an Ethernet POWERLINK network, one of the nodes, for
example a PLC, motion controller or industrial PC, is designated
to function as the Managing Node (MN), the master in the
network. All other devices operate as Controlled Nodes (CN),
slaves in the network. The MN defines the clock pulse for the
synchronization of all devices and manages the data
communication cycle. In the course of one clock cycle within
which all nodes are addressed, the MN sends Poll Requests
(PReq) to all CNs one after another. They reply immediately to the
prompts with Poll Responses (PRes).
An Ethernet POWERLINK cycle consists of three phases. During
the start phase, the MN sends a Start of Cycle Frame (SoC) signal
to all CNs to synchronize the devices. Payload data exchange
then proceeds in the second phase, the isochronous phase. The
third phase, the asynchronous phase, allows the transfer of large
packets that are not time-critical, for example parametrization
data.
PReq
CN2
Asynchronous
phase
Isochronous
phase
PReq
CN1
PRes
CN1
PRes
CN2
SoC
PReq
CNn
PRes
CNn
SoA
Async
data
MN
CN
Ethernet POWERLINK communication cycle
Start
phase
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