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Manual – MOVI-PLC® advanced DHR41B for EtherNet/IP, Modbus/TCP and PROFINET IO
7
Examples for data exchange via Modbus/TCP
Configuration and Startup (Modbus/TCP)
7.5.1
Writing and reading process data
The process data exchange can be performed either via FC3 (read) and FC16 (write),
or FC23 (read and write):
For writing 3 process data words (setpoints) to a Modbus/TCP slave via FC16, the
TCP/IP telegram to port 502 is structured as illustrated above.
Only bytes 0-11 are returned in the response telegram of port 502 of the Modbus/TCP
slave, where all values remain unchanged with the exception of byte 5. Byte 5 (low byte
length field) is corrected to value 6.
Byte Value
Meaning
Interpretation
Help
0
0x00
Transaction identifier
For a detailed description,
refer to Modbus/TCP specifi-
cation and section 'Modbus
protocol (Modbus/TCP)'
1
2
0x00
Protocol identifier
3
4
0x00
Length field
Number of bytes after byte 5:
3 (no. of PD)
×
2 + 7 = 13
5
0x0d
6
0xFF
Unit identifier
Must be 0 or 255
7
ox10
Function code
Service = FC16 (write register)
8
0x00
Write reference number
Offset from where on the PD is
located:
Must always be 4
9
0x04
10
0x00
Write word count
Number of PDW (here 3):
Must for PD 1 64
11
0x03
12
0x06
Write byte count
Number of PDW
×
2 = 6
13
0x00
Data
Process output data word 1
Data mapping and definition,
see IEC program
14
0x11
15
0x22
Process output data word 2
16
0x33
17
0x44
Process output data word 3
18
0x55
Содержание DHR41B
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