CRC in IQANdesign 6.08

chuck emmons 2 years ago in IQANdesign updated by Gustav Widén (System support) 2 years ago 3

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CRC Test.idsx

This idsx calculates the CRC correctly. however the receiver will not accept unused bits set to 1. The CRC simulator calculates correctly. How can we set unused bits to 0?

Maybe I misunderstood the question, but in your application you have the GFOUT property for "Unused bits" on Set to 1

With this property you can change it so that unused bits are set to 0. 

It does not calculate the crc correctly if unused bits is set to 0.  

Ok, I think I see what the problem is now. 

In the printscreen from the calculator, you have CRC over a four bytes with values 0x00, 0x00, 0x01, 0x00. 

The application is very different, it has has DLC 3, so the 1 byte CRC is over two bytes. 

In the case where you get the same result as the calculator, it is more by chance. The unused bits set 1 one means you feed it 2 bytes with values 0xC1, 0xF0 

(the application also has a different final XOR compared to the calculator)

I modified your application example to use the same input as the calculator, so DLC 5 with input 0x00, 0x00, 0x01, 0x00

here is how both variants look next to one another:

CRC Test forum question.idsx