Sercos stands for SErial Realtime COmmunication System. The Sercos interface is a standardized (IEC 61491 and EN 61491) digital interface for communication between controllers and drives.
oRing topology (copper)
oMaster-slave system
oBaud rate 100 MBaud
oCycle time 1 ms
oSynchronization (jitter < 1 microsecond)
Communication with Sercos is divided into two main options:
oCyclical communication
oNon-cyclical communication
The options can be used simultaneously.
The cyclical communication is used for exchanging real-time data (for example, Ref/Actual values) and is executed once in every communication cycle (CycleTime). Certain specified data is transferred from the controller to the drives and from the drives to the controller in every cycle.
Non-cyclical communication is used to exchange data such as parameters for configuring communication (cycle time), the drive parameters, status, and so on, where time is not a critical factor. The PacDrive controller controls non-cyclical communication. The of the parameters in the system can be contacted using this channel, even parameters that are configured cyclically.
Non-cyclical communication is slower than cyclical communication since the data is transferred in portions. Typically, 10-100 ms are required to read a variable.
Cyclical Data Exchange - Synchronization of Cyclical Data
Sercos enables the processing cycle of the controller to be synchronized with data exchange and the control cycle in the drive. Because of this, there is no interference between these individual cycles and the control loops have a minimum, constant dead time. This also means that the new reference value goes into effect in the drives at the same time and that the bus slaves record the measure values that they forward to the PacDrive controller as actual values at the same time. The transfer cycles must always be equidistant. The cyclical data must be correct and punctual (unpunctual data is worthless).
After an 8505 "Sercos Master comm.disturbance detected" has been reported, you can continue to work for the duration of one communication cycle with the most recent valid data or an expected value. The incorrectly transferred data will not be sent again (in order to correct the errors) because new reference values are sent in the next communication cycle (for example, 1 ms later). When several transfer errors occur in a row, the diagnostic message 8506 "SERCOS Master comm. not possible" is triggered and the bus is stopped.
Communication Phase 0
Check whether the number of connected devices remains constant and which topology is used. Then, a switchover to phase 1 is effected with the determined topology.
Communication Phase 1
Check whether the number of connected devices remains constant and which topology is used. Then, a switchover to phase 1 is effected with the determined topology.
Communication Phase 2
The master exchanges important communication parameters and data on general device properties with each slave sequentially. This defines and fixes the configuration of the cyclical channel. If the bus slaves are configured, communication phase 3 becomes active.
Communication Phase 3
Parameter phase the master exchanges parameters with the slaves. The slaves can be addressed at once. Real-time data is not available yet.
Communication Phase 4
Operating phase Cyclical exchange of real-time data (cyclical communication) Any number of parameters can be read and written using the service channel (non-cyclical communication).
Initializing of Parameters of Sercos Slaves
The parameters of the Sercos slaves are set to default values when the Sercos bus has not been started. When the Sercos bus is shut down from the operating phase (phase 4), these parameters are reset to the default values.
