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Section 7 Modbus Communications Protocol
RFID System
User's Manual
(Modbus TCP)
Section 7
Host Communications Specifications
Response Format
Normal End
Transaction Identifier
A copy of the value that was specified in the query is returned.
Protocol Identifier
This field is always 0000 hex.
Field Length
The number of bytes inclusively from the unit identifier through the end of the data is specified.
Byte 4 will always be 00 hex.
Unit Identifier
This field is always FF hex.
Function code
The value that was specified in the query (Read: 03 hex or Write: 10 hex) is set.
Data
The data for the function code is sent.
The format of the data depends on the function code.
The Reader/Writer supports the following data type.
Function code Function
03 hex Read Holding Register
10 hex Write Holding Register
Data name Description
Holding register Read/write 16-bit data
Byte 0 Byte 1 Byte 2 Byte 3 Byte 4 Byte 5 Byte 6 Byte 7 Byte 8 Byte 9 ··· Byte n
Transaction
identifier
Protocol identifier Field length
Unit
identifier
Function
code
Data
Copy of the transaction
identifier that was specified
in the query
Always 0000 hex
Always
00 hex
No. of
bytes
Always
FF hex
Range specified with the field length
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