CCITT CRC Generator Algorithm revised 9-21-96

To generate the CRC FCS for Project

1.  Create an array of bits, 16 bits long, to serve
as the CRC register.

2.  Load the array with the first 16 bits of data,
inverted, starting with the most significant bit.

3.  Shift in the remaining data.  Call the most 
significant bit being shifted out of the register 
"MSB"; immediately after each shift, use the exiting
MSB to do the following (^ means exclusive or):

a. bit 0 = MSB ^ bit 0

b. bit 5 = MSB ^ bit 5

c. bit 12 = MSB ^ bit 12

4. After all data have been entered, continue step
3 with 16 zero bits.

5. Invert the bits in the register. They now form 
the FCS.