SEW-Eurodrive DHR41B, Manual

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Manual – MOVI-PLC® advanced DHR41B for EtherNet/IP, Modbus/TCP and PROFINET IO
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8
Protocol structure
The Modbus Protocol (Modbus/TCP)
8.2.4 Service FC23 Read/write multiple registers
With the service FC23 Read/write multiple registers , you can simultaneously write and
read a variable number of registers. The write access is carried out first. Preferably, this
service is used for the process data (see following picture).
Example Request:
Response:
Exception:
64071AXX
MBAP Header Function Code-Data (FC23)
Bytes
(N)
(1...N)
FC
(0x17)
T- ID (0x00) Prot-ID (0x00) UI-D
Length
(1+10+N)
Read Address Write Address Write Data ReadWord
Count
Write Word
Count
Byte Designation Meaning/permitted values
0 - 6 MBAP header See chapter 'Header'.
7 Function code Requested service: 23 (Read/Write Multiple Registers)
8 Read reference number
(high) Offset
9 Read reference number
(low) Offset
10 Read word count (high) Number of words (register) always 0
11 Read word count (low) Number of words (register)
12 Write reference number
(high) Offset
13 Write reference number (low) Offset
14 Write word count (high) Number of words (register) always 0
15 Write word count (low) Number of words (register)
16 Write byte count 2* Word count
17 ... Write register values 2 - ... Data bytes depending on the length
Byte Designation Meaning/permitted values
0 - 6 MBAP header See chapter 'Header'.
7 Function code Service: 23 (Read/Write Multiple Registers)
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 97
hex
8 Exception code Fault code
0 0
I