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Manual – MOVI-PLC® advanced DHR41B for EtherNet/IP, Modbus/TCP and PROFINET IO
69
8
Protocol structure
The Modbus Protocol (Modbus/TCP)
8.2.2
Service FC3 Read holding registers
With the service
FC3 Read holding registers
, you can read a variable number of regis-
ters (see following figure).
Example
Request:
Response:
Exception:
64065AXX
MBAP Header
Function Code-Data(FC03)
FC
(0x03)
Read Address
Read WordCount
T- ID (0x00)
Prot-ID (0x00)
Length (1+5)
UI-D
Byte
Designation
Meaning/permitted values
0 - 6
MBAP header
See chapter 'Header'.
7
Function code
Requested service: 3 (Read Holding Register)
8
Reference number (high)
Offset
9
Reference number (low)
Offset
10
Word count (high)
Number of words (register)
11
Word count (low)
Number of words (register)
Byte
Designation
Meaning/permitted values
0 - 6
MBAP header
See chapter 'Header'.
7
Function code
Service: 3 (Read Holding Register)
8
Byte count
Number of following bytes
9....
Data
2 - ... Data bytes depending on the length
Byte
Designation
Meaning/permitted values
0 - 6
MBAP header
See chapter 'Header'.
7
Function code
83
hex
8
Exception code
Fault code
0
0
I
Содержание DHR41B
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