Autonics SPR Series, User Manual For Communication

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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 Starting address
No. of points Error check (CRC16)
High Low High Low Low High
1Byte 1Byte 1Byte 1Byte 1Byte 1Byte 1Byte 1Byte
(2) Response (Slave)
Slave address Function Byte count Data
Data Data Error check (CRC16)
High Low High Low High Low Low High
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 Starting address
No. of points Error check (CRC16)
High Low High Low Low High
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)
High Low High Low Low High
11 H 03 H 04 H 02 H 2B H 00 H 64 H ## H ## H
CRC16
CRC16