Function Code Fc23 (Read/Write Multiple Registers); Table 103: Request Of Function Code Fc23; Table 104: Response Of Function Code Fc23; Table 105: Exception Of Function Code Fc23 - WAGO -I/O-SYSTEM 750 XTR Manual

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11.2.3.11 Function Code FC23 (Read/Write Multiple Registers)

This function performs a combination of a read and write operation in a single
request. The function can write the new data to a group registers, and then return
the data of a different group. The write operation is performed before the read.
Request
The reference numbers (addresses) are zero-based in the request message;
therefore, the first register is at address 0.
The request message specifies the registers to read and write. The data is sent
as 2 bytes per register.
Example: The data in register 3 is set to value 0x0123, and values 0x0004 and
0x5678 are read out of the two registers 0 and 1.

Table 103: Request of Function Code FC23

Byte
Byte 0, 1
Byte 2, 3
Byte 4, 5
Byte 6
Byte 7
Byte 8, 9
Byte 10, 11
Byte 12, 13
Byte 14, 15
Byte 16
Byte 17...(B+16) Register values (B = Byte count)
Response

Table 104: Response of Function Code FC23

Byte
...
Byte 7
Byte 8
Byte 9...(B+1)
Exception

Table 105: Exception of Function Code FC23

Byte
...
Byte 7
Byte 8
Field name
Transaction identifier
Protocol identifier
Length field
Unit identifier
MODBUS function code
Reference number for read
Word count for read (1...125)
Reference number for write
Word count for write (1...100)
Byte count (2 x word count for write)
Field name
MODBUS function code
Byte count (2 x word count for read)
Register values (B = Byte count)
Field name
MODBUS function code
Exception code
Fieldbus Communication 167
Example
0x0000
0x0000
0x000D
0x01 not used
0x17
0x0000
0x0002
0x0003
0x0001
0x02
0x0123
Example
0x17
0x04
0x0004 or 0x5678
Example
0x97
0x01 or 0x02
Version 1.3.0
Manual