CRC Checksum explained

[josefodunga]

Hi,

I've been trying hard to understand the checksum and how it is calculated.
I wanted to check on a CRC XModem calculator the checksum done by the Video VBox.

I've been acquiring the rs232 stream and plugging this value into the calculator but every time I plug the hex values into the calculator it gives me a different value on the CRC.

For example this is the $NEWCAN message: 244E455743414E2C000000002C2541
and the checksum is 2541 but on my calculator it gives me either 0x0000, 9CA0 or 8D53.
I think the CRC polynom is 4129 (supposedly racelogic uses the XModem but Xmodem is 8408) but I was wondering what is the CRC order, the initial value and the final XOR value.

I'm not well versed in signal transmission and error correction so this is a little hard for me:confused: .

I'm thinking maybe I should just do a program to compute the CRC with what was supplied in the datasheet and not worry about anything else.

Any and all help appreciated.

[Newland46]

The check sum returned will be different for each message sent, as it is calculated using every bit within the message frame.

As the data is changing each time, this check sum will be different so the fact you are getting different values each time is correct.

I have attached the Video VBOX RS232 format to this post for your reference (if you dont have it already).

Hope this helps.

Newland#46