Error Detection with Cyclic Redundancy Check

CRC error detection computes the remainder of a polynomial division of a generator polynomial into a message. The remainder, which is usually 16 or 32 bits, is then appended to the message. When another remainder is computed, a nonzero value indicates an error. Depending on the generator polynomial's size, the process can fail in several ways, however. It is very difficult to deturmine how effective a given CRC will be at detecting errors. The probability that a random code word is valid (not detectable as an error), is completely a function of the code rate: 1 - 2^{-(n - k)}. Where n is the number of bits of formed from k original bits of data , (n - k) is the number of redundant bits, r

Use of the CRC technique for error correction normally requires the ability to send retransmission requests back to the data source.

Dr. Imre Bartfai's CRC16 and 32 for the PIC and SX microcontrollers

See also:

http://www.dalsemi.com/DocControl/PDFs/app27.pdf
Super fast CRC16 By Nikolai Golovchenko for the SX microcontroller
CRC16 by Charles Ader with matching CRC routines for SX, PIC, 8051, and x86
+ PIC Microcontroller Bit Math Method - CRC16 - standard X.25 (and XMODEM)
Ken Websters PIC16C74 serial port multiplexer. This includes checksum code for both the PIC and C++ code for the PC.
Painless guide to CRC by Ross Williams; The CRC Pitstop by Ross Williams
CRC online Calculator and Examples
CRC C code
a very compact (no-tables) CRC-16 function in C (for Modbus) from Spehro Pefhany. (CRC-16 implementations using tables are *much* faster, but also require more program space).
"How do I generate a CRC (Cyclic Redundancy Check) using a PIC?" a very compact (no-tables) CRC-16 function in PIC assembly (for X.25 and XMODEM) from Andrew Warren.
CRC Delphi and BASM Code
16 BIT CRC for XMODEM
Quick CRC Methods for XMODEM +
see also:
- http://atlas.csd.net/~cgadd/knowbase/CRC0001.HTM for x86 asm code
- http://www.agt.net/public/aerosoft/checks.htm

Questions:

-Remove-r.relamjrspam at spamverizon.net asks: " how can i fix the frame when i get a cyclic redundancy check so i can view the video" +

Comments:

There is a little mistake in the sentence regarding the probability that a random code word is not detectable as an error: It is not 1 - 2^-r but 2^-r instead (r = n - k). 1 - 2^-r gives the rate of detectable errors !+

David A Cary Says:

16-bit CRC routine (isochronous) for the polynomial 0x8005
Scott Dattalo, Dave Dribin (2002-08-24)
http://www.piclist.org/techref/postbot.asp?by=time&id=piclist\2002\08\24\233838a&tgt=post

A quick guide to CRC: With example calcuation of CRC 16 by Pierre Desrochers +

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