CRC calculation with VCU

Amtech

Genius 4585 points

Other Parts Discussed in Thread: TMS320F28069

i am working to calculate CRC-16 (poly-0X8005) with VCU unit present in TMS320F28069.

When i am using the assembly routine given in "Control suite by TI" to calculate crc i get the result like this website

i have an existing code for crc calculation in c which is working same as this excel sheet.

an example 01hex data i get these answers

0X8005 from VCU

and 0x1AFF with my c algorithm..

Is there any thing that i am missing or do i need to pre process something to my data string before feeding it to VCU?

over 13 years ago

0 Vishal_Coelho over 13 years ago

TI__Mastermind 20850 points

The modbus algorithm is a reflected algorithm, in that, the bits are shifted out from the least significant position. The VCU calculates the CRC bytewise based on the value of the MSb. The VCU cannot support the modbus algorithm. I have attached a C algorithm for modbus that you might find useful.

4718.F28069_Modbus_CRC_TableLookup_120920.zip

Also, this link is very helpful in explaining the different ways you can calculate the CRC using the same polynomial: http://www.repairfaq.org/filipg/LINK/F_crc_v3.html

0 Amtech over 13 years ago in reply to Vishal_Coelho

Genius 4585 points

can I do some pre-processing on data (like reflecting data bytes) to use this vcu unit?

0 Vishal_Coelho over 13 years ago in reply to Amtech

TI__Mastermind 20850 points

Hmm, no I dont think so. Modbus not only is a reflected algorithm, it also uses a reflected polynomial. So in the spreadsheet, if you read the polynomial left to right its actually XORing with 0x A001 and not 0x8005. The VCU has fixed polynomials for the CRCs

0 Keyur Acharya over 13 years ago in reply to Vishal_Coelho

Expert 1740 points

Actually you CAN calculate modbus crc with VCU module. but for that you have to give data in bit by bit reflected manner and take the answer in bit by bit reflected manner.

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CRC calculation with VCU