Odd that Dan should mention ModBus's CRC, 'cos that's what I've used in the end. I need my CRC to be 'open' (reproduceable by a code writer 'at the other end'), and I can't find anything that seems to be well documented, absolutely specific and universally accepted (and easy to prove) as the ModBus algorithm. My code executes in ~112 clock cycles (conventional 8051) and is not table based.
Dave