Does anyone have C code or ASM code of CRC calculation for an array of 256 byte data?
You can search yourselves.
http://www.maxim-ic.com/appnotes.cfm/appnote_number/542/ln/en
You can find a couple of CRC calculators here: http://www.8052.com/codelib.phtml
"...a couple of CRC calculators..." There are many CRCs - you will, obviously, have to decide which one you want/need to use!
A nice online tutorial on CRC algorithms: http://www.repairfaq.org/filipg/LINK/F_crc_v3.html