1 Modbus RTU Protocol
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1.3 Read holding registers (Func 03–03H)
Read the Binary data of Holding Registers (4X reference) in Slave device.
(1) Query (Master)
Slave address Function
1Byte 1Byte 1Byte 1Byte 1Byte 1Byte 1Byte 1Byte
(2) Response (Slave)
Slave address Function
Byte count
Data Data Data Error check (CRC16)
1Byte 1Byte 1Byte 1Byte 1Byte
1Byte
1Byte
1Byte 1Byte
1Byte 1Byte
If read the 2 values from Holding Register 400001 (0000 H) to 400002 (0001 H), in Slave
(Address 17) from the Master.
Query (Master)
Slave address Function
11 H 03 H 00 H 00 H 00 H 02 H ## H ## H
If the value of 400001 (0000 H) on Slave is “555 (22B H)” and the value of 400002 (0001 H) is
“100 (64 H)”.
Response (Slave)
Slave address Function
Byte count
Data Data Error check (CRC16)
11 H 03 H 04 H 02 H 2B H 00 H 64 H ## H ## H