Mitsubishi Electric MELSEC iQ-RJ71C24-R2 - Page 543

APPENDICES APPENDIX
Appendix 5 Operation Image and Data Structure of Predefined Protocol
541
A
Ex.
The calculation example of 16-bit CRC (for MODBUS)
Packet example:
Calculation method of 16-bit CRC (for MODBUS) for the above packet example
Station number Function code 16-bit CRC
02H 07H 41H 12H
CRC error checking procedure 16-bit register (MSB) Flag Calculating
procedure
(Load a 16-bit register whose bits are all '1')
02H (Station number)
Exclusive OR (XOR)
1111 1111
-
1111 1111
1111 1111
0000 0010
1111 1101
- 1 to 2
Shift 1
Generator polynomial
Exclusive OR (XOR)
0111 1111
1010 0000
1101 1111
1111 1110
0000 0001
1111 1111
1 3 to 4
Shift 2
Generator polynomial
Exclusive OR (XOR)
0110 1111
1010 0000
1100 1111
1111 1111
0000 0001
1111 1110
15
Shift 3
Shift 4
Generator polynomial
Exclusive OR (XOR)
0110 0111
0011 0011
1010 0000
1001 0011
1111 1111
1111 1111
0000 0001
1111 1110
0
1
Shift 5
Shift 6
Generator polynomial
Exclusive OR (XOR)
0100 1001
0010 0100
1010 0000
1000 0100
1111 1111
1111 1111
0000 0001
1111 1110
0
1
Shift 7
Shift 8
Generator polynomial
Exclusive OR (XOR)
0100 0010
0010 0001
1010 0000
1000 0001
0111 1111
0011 1111
0000 0001
0011 1110
0
1
07H (Function code)
Exclusive OR (XOR)
-
1000 0001
0000 0111
0011 1001
-6
Shift 1
Generator polynomial
Exclusive OR (XOR)
0100 0000
1010 0000
1110 0000
1001 1100
0000 0001
1001 1101
17
Shift 2
Generator polynomial
Exclusive OR (XOR)
0111 0000
1010 0000
1101 0000
0100 1110
0000 0001
0100 1111
1
Shift 3
Generator polynomial
Exclusive OR (XOR)
0110 1000
1010 0000
1100 1000
0010 0111
0000 0001
0010 0110
1
Shift 4
Shift 5
Generator polynomial
Exclusive OR (XOR)
0110 0100
0011 0010
1010 0000
1001 0010
0001 0011
0000 1001
00
00 0001
0000 1000
0
1
Shift 6
Shift 7
Shift 7
0100 1001
0010 0100
0001 0010
0000 0100
1000 0010
0100 0001
0
0
0
CRC value 12H 41H - 8