Honeywell
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.
9.2.2 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
www.honeywell.com/imc
CD3000M-2PH from 125A to 700A
Most significant byte Least significant Byte
Least significant Byte
Most significant byte
32
User's Manual
Least significant bit
Most significant bit