B&B Electronics MODSCAN32 - Manual - Manual (Page 11)

11
The step by step procedure to form the CRC-16 is as follows:
1.
Load a 16-bit register with all 1’s.
2.
Exclusive OR the first 8-bit byte with the high order byte of the 16-bit register, putting the result in
the 16-bit register.
3.
Shift the 16-bit register one bit to the right.
4a.
If the bit shifted out to the right is one, exclusive OR the generating polynomial 1010 0000 0000
0001 with the 16-bit register.
4b.
If the bit shifted out to the right is zero; return to step 3.
5.
Repeat steps 3 and 4 until 8 shifts have been performed.
6.
Exclusive OR the next 8-bit byte with the 16-bit register.
7.
Repeat step 3 through 6 until all bytes of the message have been exclusive OR’rd with the 16-bit
register and shifted 8 times.
8.
The contents of the 16-bit register are the 2 byte CRC error check and is added to the message
most significant bits first.
16-BIT REGISTER MSB Flag
(Exclusive OR) 1111 1111 1111 1111
02 0000 0010
1111 1111 1111 1101
Shift 1 0111 1111 1111 1110 1
Polynomial 1010 0000 0000 0001
1101 1111 1111 1111
Shift 2 0110 1111 1111 1111 1
Polynomial 1010 0000 0000 0001
1100 1111 1111 1110
Shift 3 0110 0111 1111 1111 0
Shift 4 0011 0011 1111 1111 1
Polynomial 1010 0000 0000 0001
1001 0011 1111 1110
Shift 5 0100 1001 1111 1111 0
Shift 6 0010 0100 1111 1111 1
Polynomial 1010 0000 0000 0001
1000 0100 1111 1110
Shift 7 0100 0010 0111 1111 0
Shift 8 0010 0001 0011 1111 1
Polynomial 1010 0000 0000 0001
1000 0001 0011 1110
07 0000 0111
1000 0001 0011 1001