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7
Data transmission with PDO and SDO
ID 441896.05
WE KEEP THINGS MOVING
Operation manual
24
7.1
Process data transmission with PDO service
Process data is transferred by the master cyclically after every pass of the PLC
task. STÖBER ANTRIEBSTECHNIK devices provide four PDO channels. Each
PDO channel has one reception direction (rx) and one transmission direction (tx)
from the point of view of the device.
It is possible to operate up to four independent PDO channels simultaneously. All
data from all PDO channels is transferred in direct sequence with EtherCAT.
The parameters that are defined as the content of these PDOs appear in the
control program of the EtherCAT master as
variables
.
7.1.1
Process data mapping
Process data imaging specifies which parameters (communication objects) will
be transferred with the process data channel (PDO service). The devices of the
5th generation of STÖBER inverters support flexible imaging of the
communication objects on the PDO channels. This mechanism is called PDO
mapping.
PDO mapping
One parameter with six sub-elements for each sending direction exists for each
PDO channel on the inverter. The addresses of the parameters are entered in the
sub-elements whose contents are then transferred via the PDO channel. Based
on the number and size of the entered objects the inverter expects a certain
number of bytes in the PDO telegram. If too many bytes are received the extra
data are ignored. If too few bytes are received the incomplete target objects are
left unchanged.
Settings ...
There are two ways to set mapping:
•
In the parameter list of the POSITool software (recommended)
•
In the EtherCAT master (e.g., with Beckhoff controllers: TwinCAT System
Manager)
Both mechanisms address the mapping parameter or one of its sub-elements.
This is addressed in the SDO telegram with EtherCAT in POSITool with
STÖBER's address.
... via EtherCAT with SDO telegram
One sub-element of the mapping parameter has four bytes. The SDO telegram
writes the sub-element with index, subindex and, optionally, the bit length of the
parameter to be mapped. The bit length of the mapped parameter does not have
to be specified during transmission to the inverter. The length is supplied when
the parameter is read out of the inverter.