Honeywell
CD3000M-1PH from 125A to 700A
User’s Manual
www.honeywell.com/imc
36
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
2
16
+ 2
15
+ 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 Least significant bit
Most significant byte Least significant Byte
Reversed bit order
Least significant bit Most significant bit
Least significant Byte
Most significant byte
N.B.: Reversed order apples, so CRC16 return Reversed bit order
