Greetings:
I am trying to implement RS-485, NRZI HDLC communications between my Rabbit RCM3720 development board and some legacy ZILOG SCC based devices. To my delight, messages transmitted by the RCM3720 arrive at my legacy devices. Unfortunately, these messages, while the data is correct, fail their CRC check and are ultimately rejected.
Anyone who has investigated CRCs will be painfully aware there exists a wide variance in algorithms. I was hoping, considering the ZILOG legacy of the Rabbit designs, I might get lucky and the RCM3720 CRC implementation would match the ZILOG SCC CRC calculation. Alas, I am so close yet so far.
As my legacy devices are of course fixed, my first hope is to adjust the RCM3720 CRC algorithm. I have been unable, however, to find mention of the RCM3720 CRC function in the accumulated Rabbit documentation. Are there any CRC parameters accessible to RCM3720 users?
Failing that, we have, by much hard work and some dumb luck, duplicated the ZILOG SCC CRC algorithm in C. If I cannot modify the output of the RCM3720 CRC generator, would it be possible to disable the automatic CRC appending and manually append my own values?
Thanks for any suggestions. This would be an enormous boon to us if this could work.
Doug P.