Honeywell CD3200 User Manual page 39

User's Manual ver. 2.0
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
CD3200 up to110A
Most significant byte Least significant Byte
Least significant Byte Most significant byte
37
Honeywell
Least significant bit
Most significant bit
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