Modbus Read Holding Registers (FC03)

Function Code 03

Request

This command is requesting the content of analog output holding registers # 40108 to
 40110 from the slave device with address 17.

11 03 006B 0003 7687

11: The SlaveID (11 hex = address 17 )
03: The Function Code 3 (read Analog Output Holding Registers)
006B: The Data Address of the first register requested.
             ( 006B hex = 107 , + 40001 offset = input #40108 )
0003: The total number of registers requested. (read 3 registers 40108 to 40110) 
7687: The CRC (cyclic redundancy check) for error checking.

Response

11 03 06 AE41 5652 4340 49AD

11: The SlaveID (11 hex = address 17 )
03: The Function Code 3 (read Analog Output Holding Registers)
06: The number of data bytes to follow (3 registers x 2 bytes each = 6 bytes)
AE41: The contents of register 40108
5652: The contents of register 40109
4340: The contents of register 40110
49AD: The CRC (cyclic redundancy check).