Brent Brown wrote:
> The one thing that pushed me over the top was adding CRC
> checking for my 1 wire temperature sensors -  needed it
> because I'm getting the occasional erroneous result.
> This adds about 300 program words.

Huh!?

CRC is a really simple algorithm that shouldn't take more than a few
instructions.  For each bit you shift it in one end.  If the bit that
shifted out the other end is 0 you're done.  If it is 1, you XOR the
accumulated checksum with a fixed value.  That's it.  There are some
variations about which end to shift into, whether you do the XOR on a 0 or
1, what the accumulator is initialized to, etc.  However, none of these
should change the basic algorithm or the number of instructions required.

I just checked some recent code I wrote that computed a 16 bit CRC on bits
in a buffer.  It takes 29 instructions, which includes the initialization,
checking for end condition, advancing to the next bit, etc.  The actual CRC
update calculation is only 8 instructions once the bit is in STATUS,C.


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