Eaton PowerXL DC1, Manual

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7 Serial interface (Modbus RTU)
7.3 Operating mode Modbus RTU
DC1 Frequency Inverter 10/12 MN04020003Z-EN www.eaton.com
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7.3.1 Structure of the master request
7.3.1.1 Address
• P-36 is used to enter the address (1 to 63) of the frequency inverter to
which the request is being sent. Only the frequency inverter with this
address can respond to the request.
• Address 0 is used as a so-called Broadcast (message to all bus users)
from the master. In this mode, individual slaves cannot be addressed
and data cannot be output from the slaves.
7.3.1.2 Function code
The function code defines the type of message. The following actions can be
performed in the case of DC1 frequency inverters:
7.3.1.3 Data
The length of the data block (data: N x 1 bytes) depends on the function
code. The function code is made up of two hexadecimal values and has a
range of 00 to FF. The data block contains additional information for the slave
that will enable the latter to perform the operation specified by the master in
the function code (this information may specify the parameters that need to
be processed, for example).
7.3.1.4 Cyclic redundancy check (CRC)
Frames in the Modbus RTU operating mode include a cyclic redundancy
check (CRC). The CRC field is made up of two bytes that contain a binary 16-
bit value. The CRC is always performed independently of the parity check for
the frame's individual values. The CRC result is appended to the frame by the
master. While receiving the frame, the slave performs a new calculation and
compares the calculated value to the actual value in the CRC field. If the val-
ues do not match, an error will be set.
Function code [hex] Designation Description
03 Read Holding Registers Reading of the holding registers in the slave (process
data, parameters, configuration).
A master request enables up to 11 registers to be read.
06 Write Single Register Writing of a holding register in the slave.
With a general telegram (Broadcast) the appropriate
holding registers are written in all slaves. The register
is read back for comparison.