4. MODBUS COMMUNICATION PROTOCOL
IMR02F04-E1
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4.6 Register Read and Write
4.6.1 Read holding registers [03H]
The query message specifies the starting register address and quantity of registers to be read.
The contents of the holding registers are entered in the response message as data, divided into two parts: the
high-order 8-bit and the low-order 8-bit, arranged in the order of the register numbers.
Example: The contents of the four holding registers from 00E0H [Measured value (PV)] to
00E3H [Alarm 2 state monitor] are the read out from slave address 2.
Query message
Slave address
02H
Function code
03H
Starting No.
High
00H
Low
E0H
Quantity
High
00H
Low
04H
CRC-16 High
45H
Low
CCH
Normal response message
Slave address
02H
Function code
03H
Number of data
08H
First holding register contents
High
00H
()
Low
19H
Next holding register contents
High
00H
(
Low
00H
Next holding register contents
High
00H
(
Low
00H
Next holding register contents
High
00H
(
Low
00H
CRC-16 High
12H
Low
52H
Error response message
Slave address
02H
80H
Function code
83H
Error code
03H
CRC-16 High
F1H
Low
31H
Number of holding registers
2
First holding register address
The setting must be between 1 (0001H) and
125 (007DH).
