Appendix A Function code: 03 to read one single or multi word-device register value Data structure of request message: Data structure of response message: A-16 DVP-MC operating manual Abnormality response Explanation code 0x01 Illegal command code: command code in the command message PLC receives is invalid. 0x02 Illegal device address: the address in the command message PLC receives is invalid. 0x03 Illegal device value: the data content in the command message PLC receives is invalid. 0x07 1. Check sum error 1.1 Check if the checksum value is correct 2.
Illegal command message 2.1 Command message is too short 2.2 Command message exceed the range Data order Name Byte Byte0 Modbus ID Single byte Byte1 Function code Single byte Byte2 Read the start address of the word devices in DVP10MC11T High byte Byte3 Low byte Byte4 Read the address number of the word devices in DVP10MC11T （Counted by Words） High byte Byte5 Low byte Byte6 Low byte of CRC check sum Low byte Byte7 High byte of CRC check sum High byte Data order Name Byte Byte0 Modbus ID Single byte Byte1 Function code Single byte Byte2 Read the address number of the word devices in DVP10MC11T （Counted by Bytes） Single byte Byte3 The address content of the word devices in DVP10MC11T High byte Byte4 Low byte …
The address content of the word devices in DVP10MC11T High byte … Low byte Byte n The address content of the word devices in DVP10MC11T High byte Byte n+1 Low byte