PIC topic added ...

> So I've been working on checksums. It's clear that CRC is the best. Howev=
er it gets
> murky in terms of running CRC on 15 bit values. While there are decent 15=
 bit CRC
> polynominals out there, I've had a tough time finding any table driven al=
gorithms
> that addresses anything other than 4, 8, 16, or 32 bits. It looks like th=
e natural
> breakdown would be to split the 15 bits into three 5 bit words and use th=
ree 5 bit
> tables to encode. So the tables would cost 96 words of program memory. Bu=
t then it
> looks like some work to either split the 15 bit word into 5 bit chunks, o=
r the
> opposite of combining three 5 bit chunks into a whole 15 bit word. With s=
ome careful
> coding it would be possible to generate both at the same time I guess.

My initial thought was that the easiest way is to calculate a 16 bit CRC wi=
th the top bit of data always 0, but I guess you also need to transmit the =
CRC in a 15 bit word, but maybe the way to do that is have it as a special =
word.

But if the comms are one way, how are you going to signify an error?


--=20
Scanned by iCritical.

--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.