Honeywell CD3000M-1ph User Manual page 38

User's Manual
Since only the RTU form of the protocol is supported, each message is followed by a two-byte
CRC 16 (a 16-bit cyclic redundancy checksum).
This checksum is calculated in accordance with a formula which involves recursive division of the
data by a polynomial, with the input to each division being the remainder of the results of the
previous division.
The dividing polynomial is
16 15 2
2 + 2 + 2 + 1(Hex 18005)
but this is modified in two ways:
because the bit order is reversed, the binary pattern is also reversed, making the most
•
significant bit (MSB) the right-most bit;
because only the remainder is of interest, the right-most (most significant) bit can be
•
discarded.
Thus, the polynomial has the value Hex A001.
10.2.2 Bit's order
Normal bit order
Most significant bit
Reversed bit order
Least significant bit
N.B.: Reversed order apples, so CRC16 return Reversed bit order
CD3000M-1PH up to 110A
Most significant byte Least significant Byte
Least significant Byte Most significant byte
37
Honeywell
Least significant bit
Most significant bit
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