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162
Se
ct
io
n 7
Mo
dbus
Commun
ic
a
tion
s
Prot
ocol
RFID System
User's Manual
(Modbus TCP)
Section 7
Host Communications Specifications
Function Code Descriptions
Read Holding Register (03 Hex)
This function code is used to read the contents of the specified number of continuous holding registers
starting from the specified address.
Example: Reading Four Words of Data Starting from Address 1234 Hex in the
RF Tag
Query
The address in the RF Tag is the same as the register address.
Response
No.
Field name
Example
(hex)
1
Transaction identifier upper byte
00
2
Transaction identifier lower byte
00
3
Protocol identifier upper byte
00
4
Protocol identifier lower byte
00
5
Field length upper byte
00
6
Field length lower byte
06
7
Unit identifier
FF
8
Function code
03
9
Register address upper byte (See note 1.)
12
10
Register address lower byte (See note 1.)
34
11
Word count upper byte
00
12
Word count lower byte
04
RF Tag address = Register address
No.
Field name
Example
(hex)
1
Transaction identifier upper byte
00
2
Transaction identifier lower byte
00
3
Protocol identifier upper byte
00
4
Protocol identifier lower byte
00
5
Field length upper byte
00
6
Field length lower byte
0B
7
Unit identifier
FF
8
Function code
03
9
Byte count
08
10
Read data 1 upper byte
11
11
Read data 1 lower byte
11
12
Read data 2 upper byte
22
13
Read data 2 lower byte
22
14
Read data 3 upper byte
33
15
Read data 3 lower byte
33
16
Read data 4 upper byte
44
17
Read data 4 lower byte
44