Generating a CRC 
 
Step 1 Load a 16-bit register with FFFF hex (all 1's). Call this the CRC 
' register. 
 
Step 2 Exclusive OR the first eight-bit byte of the message with the low _
  order 
byte of the 16-bit CRC register, putting the result in the CRC register. 
 
Step 3 Shift the CRC register one bit to the right (toward the LSB), _
  zerofilling 
the MSB. Extract and examine the LSB. 
 
Step 4 If the LSB is 0, repeat Step 3 (another shift). If the LSB is 1, _
  Exclusive OR
the CRC register with the polynomial value A001 hex (1010 0000 0000 0001). 
 
Step 5 Repeat Steps 3 and 4 until eight shifts have been performed. When _
  this 
is done, a complete eight-bit byte will have been processed. 
 
Step 6 Repeat Steps 2 ... 5 for the next eight-bit byte of the message. _
  Continue
doing this until all bytes have been processed. 
 
Result The final contents of the CRC register is the CRC value. 
 
Step 7 When the CRC is placed into the message, its upper and lower bytes
 must be swapped as described below. 
 
Placing the CRC into the Message 
 
When the 16-bit CRC (two eight-bit bytes) is transmitted in the message, the low 
order byte will be transmitted first, followed by the high order byte-e.g., if _
  the CRC 
value is 1241 hex (0001 0010 0100 0001):

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