NORD USS and Modbus RTU Manual
26 Subject to technical amendments BU 0050 GB-3111
1.5 Data transmission
1.5.1 Structure of reference data
This section describes the cyclic data traffic between the master and the frequency inverter.
The reference data is divided into two sections:
PKW section (Parameterisation; Parameter Identification- Value)
PZD section (Processdata)
Parameter values can be read and written via the PKW section of the reference data. All tasks which are
carried out via the PKW interface are essentially tasks for configuration, monitoring or diagnosis.
The PZD section serves to control the frequency inverter. The control word or status word as well as the
setpoint and actual values are transferred in the process data.
Access always consists of an order and a response telegram. In the order telegram, the reference data is
transferred to the slave. In the response telegram, the reference data is transferred from the slave to the
master. The structure of both telegrams is identical.
Telegram traffic / structure of reference data area
Processing of the process data is carried out immediately in the FI (high priority), in order to ensure a rapid
reaction to control commands or a change in status can be transmitted to the master without delay.
On the other hand, the processing speed of the PKW data has a lower priority, so that processing may take
considerably longer.
Status word + Actual value
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