Mitsubishi MELSEC LJ71C24, User Manual

Page: 382 / 428

App. - 53 App. - 53
APPENDIXES
The following show the example of 16-bit CRC (for MODBUS) calculation.
Packet example:
Station No. Function code 16-bit CRC
02
H
07
H
41
H
12
H
Procedure example of 16-bit CRC (for MODBUS) of a packet example above:
CRC error checking procedure 16-bit register (MSB) Flag
Calculating
procedure
(Load a 16-bit register whose bits are all '1')
1111 1111 1111 1111
02
H
(Station number)
0000 0010
Exclusive OR (XOR)
1111 1111 1111 1101
1) to 2)
Shift 1 0111 1111 1111 1110 1
Generator polynomial 1010 0000 0000 0001
Exclusive OR (XOR) 1101 1111 1111 1111
3) to 4)
Shift 2 0110 1111 1111 1111 1
Generator polynomial 1010 0000 0000 0001
Exclusive OR (XOR) 1100 1111 1111 1110
Shift 3 0110 0111 1111 1111 0
Shift 4 0011 0011 1111 1111 1
Generator polynomial 1010 0000 0000 0001
Exclusive OR (XOR) 1001 0011 1111 1110
Shift 5 0100 1001 1111 1111 0
Shift 6 0010 0100 1111 1111 1
Generator polynomial 1010 0000 0000 0001
Exclusive OR (XOR) 1000 0100 1111 1110
Shift 7 0100 0010 0111 1111 0
Shift 8 0010 0001 0011 1111 1
Generator polynomial 1010 0000 0000 0001
Exclusive OR (XOR) 1000 0001 0011 1110
5)
07
H
(Function code) 0000 0111
Exclusive OR (XOR) 1000 0001 0011 1001
6)
Shift 1 0100 0000 1001 1100 1
Generator polynomial 1010 0000 0000 0001
Exclusive OR (XOR) 1110 0000 1001 1101
Shift 2 0111 0000 0100 1110 1
Generator polynomial 1010 0000 0000 0001
Exclusive OR (XOR) 1101 0000 0100 1111
Shift 3 0110 1000 0010 0111 1
Generator polynomial 1010 0000 0000 0001
Exclusive OR (XOR) 1100 1000 0010 0110
Shift 4 0110 0100 0001 0011 0
Shift 5 0011 0010 0000 1001 1
Generator polynomial 1010 0000 0000 0001
Exclusive OR (XOR) 1001 0010 0000 1000
Shift 6 0100 1001 0000 0100 0
Shift 7 0010 0100 1000 0010 0
Shift 8 0001 0010 0100 0001 0
7)
CRC value 12
H
41
H
8)