Modbus CRC16 generation question

[xiaozhao]

Dear guys

        I have a problem in the edit the CRC16 code,i can't get the CRC16 checksum is same as the correct command list showing.pls help to have a look about my Vi,if have a bug or no attention point,thanks a lot.attached my vi,fyi.

[xiaozhao]

I want to send the string"01 03 00 00 00 08",then generate a CRC "0C 44",but the result is not my attention.

[K C]

Hi,

To start with your second post. The ModBus CRC of the command you give is not 0x0C44 but it is 0x440C

In you program you convert a string into a byte array. If you convert the slave address '01' as a string into a byte array you will get two bytes 0x30 and 0x31. The are ascii character and what you need is a single byte with the value of 0x01.

If change your VI.

Kees

[xiaozhao · Accepted solution]

Dear Kees,

        Thanks a lot.i got it.i use labview 13.0 version,i can't open you VI,but i have change my vi,now it can meet the result when swap the low 8bit and high 8bit,thanks a lot again.i'm misguided by the meter communication spec.

[K C]

To be complete. Here is the LV 2013 version.

Kees

[noahc]

(*bump*) I have attached your code with the incorporated byte swap for version 2018. Kees' version appended two zero-value bytes that made the Modbus CRC calculation invalid, and your approach seemed more straightforward.