GE PACSystems RX7i Reference Manual

Chapter 6. Serial I/O, SNP & RTU Protocols
234 PACSystems* RX7i, RX3i and RSTi-EP CPU Reference Manual GFK-2222AD
Transmitter CRC-16 Algorithm
Receiver
84
CRC-16 Algorithm
MSB
85
LSB
79
Flag
MSB
79
LSB
79
Flag
Initial Remainder
1111
1111
1111
1111
Rcvr CRC after data
1110
0010
0100
0001
XOR 1st data byte
0000
0000
0000
0001
XOR 1st byte Trns CRC
0000
0000
0100
0001
Current CRC
1111
1111
1111
1111
Current CRC
1110
0010
0000
0000
Shift 1
0111
1111
1111
1111
0
Shift 1
0111
0001
0000
0000
0
Shift 2
0011
1111
1111
1111
1
Shift 2
0011
1000
1000
0000
0
XOR Gen. Polynomial
1010
0000
0000
0001
Shift 3
0001
1100
0100
0000
0
Current CRC
1001
1111
1111
1110
Shift 4
0000
1110
0010
0000
0
Shift 3
0100
1111
1111
1111
0
Shift 5
0000
0111
0001
0000
0
Shift 4
0010
0111
1111
1111
1
Shift 6
0000
0011
1000
1000
0
XOR Gen. Polynomial
1010
0000
0000
0001
Shift 7
0000
0001
1100
0100
0
Current CRC
1000
0111
1111
1110
Shift 8
0000
0000
1110
0010
0
Shift 5
0100
0011
1111
1111
0
XOR 2nd byte Trns CRC
0000
0000
1110
0010
Shift 6
0010
0001
1111
1111
1
Current CRC
0000
0000
0000
0000
XOR Gen. Polynomial
1010
0000
0000
0001
Shift 1-8 yields
0000
0000
0000
0000
Current CRC
1000
0001
1111
1110
All errors for receiver final CRC-16 indicates transmission correct.
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
2
4
1
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:
Address
Function
CRC–16
01
07
41
E2
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.

GE PACSystems RX7i Specifications

General

Brand	GE
Model	PACSystems RX7i
Category	Controller
Language	English