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6.4.2.3
User data range of the USS telegram
The user data range of the USS protocol is used to transmit application data. This comprises
the parameter channel data and the process data (PZD).
The user data occupy the bytes within the USS frame (STX, LGE, ADR, BCC). The size of
the user data can be configured using parameters p2023 and p2022. The structure and
sequence of the parameter channel and process data (PZD) are shown in the figure below.
Figure 6-13
The length for the parameter channel is determined by parameter p2023 and the length for
the process data is specified by parameter p2022. If the parameter channel or the PZD is not
required, the appropriate parameters can be set to zero ("PKW only" or "PZD only").
It is not possible to transfer "PKW only" and "PZD only" alternatively. If both channels are
required, they must be transferred together.
6.4.2.4
Data structure of the USS parameter channel
The USS protocol defines for inverters the user data structure via which a master accesses
the slave inverter. The parameter channel is used to read and write parameters in the
inverter.
Parameter channel
You can use the parameter channel with a fixed length of 3 or 4 data words or with a variable
length.
The first data word always contains the parameter identifier (PKE) and the second contains
the parameter index.
The third, fourth and subsequent data words contain parameter values, texts and
descriptions.
Inverter with CU240B-2 and CU240E-2 Control Units
Operating Instructions, 07/2010, FW 4.3.2, A5E02299792B AA
USS user data structure
Connection to a fieldbus
6.4 Communication via RS485
135
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