Crc (Crcl,Crch) - Datavideo HS-2000 Instruction Manual

CRC (CRCL,CRCH)

Check sum! It is transmitted lower byte first.
All the bytes except the last 2 from the block are used to calculate the check sum.
There must be 0x0000 after the check sum calculation including the last 2 bytes,
if the data have been transmitted error free.
The initial value for check sum calculation is 0xFFFF.
The check sum polynomial and examples for the algorithm realization
are given in the "Application Note 27.
Understanding and Using Cyclic Redundancy Checks with
Dallas Semiconductor iButtonTM Products (www.dalsemi.com)",
in the "CRC-16 computation for ram records in iButtons" section.
CRCL and CRCH can be calculated , particularly, by means of the
tables 1 and 2 according to the rule below:
CRCH' = Tbl.2 (I),
CRCL' = Tbl.1 (I) + CRCH, where I = CRCL + InputByte
CRCH and CRCL correspond to higher and lower byte of the current
check sum value, InputByte – next data byte.
CRCH' and CRCL' correspond to higher and lower byte of
the new check sum value. Tbl.2 (I) and Tbl.1 (I) correspond to the tables' values,
I is the shift factor in the tables. «+» means bit-wise XOR.
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