Powerlink Basic Cycle

Start of Cyclic (SoC)

The manager initiates each communication cycle by transmitting a special message referred to as the SoC, which serves as a precise time sync for all devices on the network.

Isochronous Period

This period is segmented into time slots during which the manager node (MN) and controlled node (CN) exchange process data. Responses from the CN’s to the MN are transmitted multicast. This allows data to be sent to any other CN on the network at the same time, inherently providing a means of peer to peer communications embedded within the cycle.

Process Data

The data exchanged during the isochronous phase is known as Process Data Objects (PDO) and is device and application dependant. You choose what data you wish to exchange at ‘design time’. Examples would be control and status information, speed, position r torque demand for a drive, digital and analogue I/O information or perhaps absolute position from a Powerlink encoder.

Multiplexing to Optimise Bandwidth

Each of the time slots can actually be shared amongst a number of CN’s which then effectively operate at a lower cycle rate. This allows some devices to operate at an optimum fats cyclic rate and lower priority devices at lower bandwidth. This provides a great deal for design flexibility for system configuration and optimisation.

Asynchronous Period

The remaining cycle time is allocated as asynchronous communications or non-real time. The MN will grant access to this period to one of the CN’s based on a request and prioritisation scheme. Messages are standard IP messages and as such communication with the outside world for Maintenance or production monitoring and control can take place.

Service Data

During the asynchronous period devices can request or respond with Service Data object (SDO) messages which can contain any available information which is generally not time critical. This can be for control purposes such as gain changes, or configuration and maintenance purposes from outside the Powerlink network.