GE PACSystems RX7i Reference Manual page 245

Chapter 6. Serial I/O, SNP & RTU Protocols
Transmitter CRC-16 Algorithm
MSB
Initial Remainder 1111 1111 1111 1111
XOR 1st data byte 0000 0000 0000 0001
Current CRC 1111 1111 1111 1111
Shift 1 0111 1111 1111 1111 0
Shift 2 0011 1111 1111 1111 1
XOR Gen. Polynomial 1010 0000 0000 0001
Current CRC 1001 1111 1111 1110
Shift 3 0100 1111 1111 1111 0
Shift 4 0010 0111 1111 1111 1
XOR Gen. Polynomial 1010 0000 0000 0001
Current CRC 1000 0111 1111 1110
Shift 5 0100 0011 1111 1111 0
Shift 6 0010 0001 1111 1111 1
XOR Gen. Polynomial 1010 0000 0000 0001
Current CRC 1000 0001 1111 1110
Shift 7 0100 0000 1111 1111 0
Shift 8 0010 0000 0111 1111 1
XOR Gen. Polynomial 1010 0000 0000 0001
Current CRC 1000 0000 0111 1110
XOR 2nd data byte 0000 0000 0000 0111
Current CRC 1000 0000 0111 1001
Shift 1 0100 0000 0011 1100 1
XOR Gen. Polynomial 1010 0000 0000 0001
Current CRC 1110 0000 0011 1101
Shift 2 0111 0000 0001 1110 1
XOR Gen. Polynomial 1010 0000 0000 0001
Current CRC 1101 0000 0001 1111
Shift 3 0110 1000 0000 1111 1
XOR Gen. Polynomial 1010 0000 0000 0001
Current CRC 1100 1000 0000 1110
Shift 4 0110 0100 0000 0111 0
Shift 5 0011 0010 0000 0011 1
XOR Gen. Polynomial 1010 0000 0000 0001
Current CRC 1001 0010 0000 0010
Shift 6 0100 1001 0000 0001 0
Shift 7 0010 0100 1000 0000 1
XOR Gen. Polynomial 1010 0000 0000 0001
Current CRC 1000 0100 1000 0001
Shift 8 0100 0010 0100 0000 1
XOR Gen. Polynomial 1010 0000 0000 0001
Transmitted CRC 1110 0010 0100 0001
E
84
The receiver processes incoming data through the same CRC algorithm as the transmitter. The example for the receiver starts
at the point after all the data bits but not the transmitted CRC have been received correctly. Therefore, the receiver CRC
should be equal to the transmitted CRC at this point. When this occurs, the output of the CRC algorithm will be zero indicating
that the transmission is correct.
The transmitted message with CRC would then be:
85
The MSB and LSB references are to the data bytes only, not to the CRC bytes. The CRC MSB and LSB order are the reverse of
the data byte order.
234
85 79
LSB Flag
2 4 1
Address Function
01
PACSystems* RX7i, RX3i and RSTi-EP CPU Reference Manual
Receiver
Rcvr CRC after data
XOR 1st byte Trns CRC
Current CRC
Shift 1
Shift 2
Shift 3
Shift 4
Shift 5
Shift 6
Shift 7
Shift 8
XOR 2nd byte Trns CRC
Current CRC
Shift 1-8 yields
All errors for receiver final CRC-16 indicates transmission correct.
CRC–16
07 41 E2
84
CRC-16 Algorithm
79 79
MSB LSB
1110 0010 0100 0001
0000 0000 0100 0001
1110 0010 0000 0000
0111 0001 0000 0000
0011 1000 1000 0000
0001 1100 0100 0000
0000 1110 0010 0000
0000 0111 0001 0000
0000 0011 1000 1000
0000 0001 1100 0100
0000 0000 1110 0010
0000 0000 1110 0010
0000 0000 0000 0000
0000 0000 0000 0000
Flag
0
0
0
0
0
0
0
0
GFK-2222AD