There is some confusion about the "correct" initial value of the 16-bit CCITT CRC. See CRC-CCITT -- 16-bit (other source) which explains it.
It has to do with the question of "augmented" zero bits at the end of the message, and an algorithm that can avoid the need for it, but needs a modification to the initial value. See Chapter 10, "A Slightly Mangled Table-Driven Implementation", of A Painless Guide to CRC Error Detection Algorithms for an explanation.
In short, perhaps pycrc's ccitt model should have an --xor-in initial value of 0x1D0F instead of 0xFFFF.
Online CRC calculator which allows calculating with "nondirect" and "direct" algorithms, and converting the initial values between these two algorithms.
There is some confusion about the "correct" initial value of the 16-bit CCITT CRC. See CRC-CCITT -- 16-bit (other source) which explains it.
It has to do with the question of "augmented" zero bits at the end of the message, and an algorithm that can avoid the need for it, but needs a modification to the initial value. See Chapter 10, "A Slightly Mangled Table-Driven Implementation", of A Painless Guide to CRC Error Detection Algorithms for an explanation.
In short, perhaps pycrc's
ccittmodel should have an--xor-ininitial value of0x1D0Finstead of0xFFFF.See also: