Appendix A Request message: Response message: 4. CRC check （ check sum ） CRC check starts from “Communication address” to the last “Data content”. The calculation method is shown below. Step 1: Download a 16-bit hex register (CRC register) with the content value FFFF. Step 2: Make the XOR operation between the 8-bit data of the first byte in the command and the 8-bit data of the low byte in CRC register and then store the operation result in CRC register. Step 3: Move the content value of CRC register by one bit towards the right and fill 0 in the highest bit. Step 4: Check the value of the lowest bit in CRC register.
If the value is 0, repeat the action of step 3; if 1, make XOR operation between the content in CRC register and hex. A001 and then store the result in CRC register. Step 5: Repeat step 3 and step 4 till the content in CRC register is moved by 8 bits towards the right. At this moment, the first byte of the command message is finished processing.
A-10 DVP-MC operating manual Field name Character Start No input data for more than 10ms Communication address 01 Function code 03 High byte of Modbus address 10 Low byte of Modbus address 00 Read high byte of data number 00 Read low byte of data number 02 Low byte of CRC check sum C0 High byte of CRC check sum CB End No input data for more than 10ms Field name Character Start No input data for more than 10ms Communication address 01 Function code 03 Read data number（Counted by bytes） 04 Read high byte of data content 01 Read low byte of data content 00 Read high byte of data content 02 Read low byte of data content 00 Low byte of CRC check sum FA High byte of CRC check sum AF End No input data for more than 10ms