Omron V680S Series User Manual page 85

Message Formats
The host device communications protocol that is used by the V680S is based on Modbus/TCP.
The command message that the host device sends to the Reader/Writer is called a query. The
response message that the Reader/Writer returns is called the response. The communications formats
for queries and responses are given below.
 Query format
Byte 0 Byte 1 Byte 2
Transaction
Protocol identifier
identifier
X X Always 0000 hex
X: Any value
Transaction Identifier
You can set any desired value. The transaction identifier in the response from the Reader/Writer will be
a copy of the value that is specified here.
Protocol Identifier
This field is always 0000 hex.
Field Length
Specify the number of bytes inclusively from the unit identifier through the end of the data.
Byte 4 will always be 00 hex.
Unit Identifier
This field is always FF hex.
Function code
Specify the function code of the function for the Reader/Writer to execute.
The applicable function codes are listed below.
Function code
03 hex Read Holding Register
10 hex Write Holding Register
Data
Send the data for the function code.
The format of the data depends on the function code.
Of the data types that are supported by Modbus communications, the Reader/Writer supports the
following data type.
Data name
Holding register
Byte 3 Byte 4 Byte 5
Field length
identifier
Always No. of Always
00 hex bytes FF hex
Function
Description
Read/write 16-bit data
Host Communications Specifications
Byte 6 Byte 7 Byte 8
Unit Function
code
03 or 10 hex
Range specified with the field length
Section 5
Byte 9 ··· Byte n
Data
RFID System
User's Manual
83