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3.3.4.3 Parameter channel
The master can request a parameter value from the slave or change a
parameter value via the parameter channel. Each parameter can be
uniquely addressed via the index and subindex.
76543210Byte
Ctrl
Subindex
Index
PV
Figure 4: Parameter channel
Ctrl Byte "Ctrl" contains the request to read or write a parameter.
The transmit data contains the information whether a parameter is to
be read or written. The receive data contains the information whether
the read request or the write request were successful.
Transmit data:
Ctrl Function
02
h
No request
12
h
Read request
22
h
Write request (word)
32
h
Write request (double word)
Receive data:
Ctrl Function
02
h
Request not yet completed
12
h
Read request or write request successfully completed (word)
22
h
Read request or write request successfully completed (double
word)
72
h
Error message
Only one request can be processed at a time. The slave provides the
response until the master sends a new request. If a response includes
parameter values, the slave responds with the current value in the
case of a repetition.
NOTE: Read requests are only executed by the slave if the value
changes from 02
h
to 12
h
. Write requests requests are only executed
by the slave if the value changes from 02
h
to 22
h
or to 32
h
.
Subindex
The byte "Subindex" must be set to the value 00
h
.
Index The word "Index" contains the parameter address.
See the product manual for a list of the parameters.
3 Basics
LXM32M
26 Modbus-TCP module
0198441113843, V1.01, 01.2012