43
XMEGA D3 [DATASHEET]
Atmel-8134N-ATxmega32D3-64D3-128D3-192D3-256D3-384D3_datasheet–03/2014
24.
CRC – Cyclic Redundancy Check generator
24.1
Features
Cyclic redundancy check (CRC) generation and checking for
Communication data
Program or data in flash memory
Data in SRAM and I/O memory space
Integrated with flash memory and CPU
Automatic CRC of the complete or a selectable range of the flash memory
CPU can load data to the CRC generator through the I/O interface
CRC polynomial software selectable to
CRC-16 (CRC-CCITT)
CRC-32 (IEEE 802.3)
Zero remainder detection
24.2
Overview
A cyclic redundancy check (CRC) is an error detection technique test algorithm used to find accidental errors in data, and
it is commonly used to determine the correctness of a data transmission, and data present in the data and program
memories. A CRC takes a data stream or a block of data as input and generates a 16- or 32-bit output that can be
appended to the data and used as a checksum. When the same data are later received or read, the device or application
repeats the calculation. If the new CRC result does not match the one calculated earlier, the block contains a data error.
The application will then detect this and may take a corrective action, such as requesting the data to be sent again or
simply not using the incorrect data.
Typically, an n-bit CRC applied to a data block of arbitrary length will detect any single error burst not longer than n bits
(any single alteration that spans no more than n bits of the data), and will detect the fraction 1-2
-n of all longer error
bursts. The CRC module in Atmel AVR XMEGA devices supports two commonly used CRC polynomials; CRC-16 (CRC-
CCITT) and CRC-32 (IEEE 802.3).
CRC-16:
Polynominal: x16+x12+x5+1
Hex value:
0x1021
CRC-32:
Polynominal: x32+x26+x23+x22+x16+x12+x11+x10+x8+x7+x5+x4+x2+x+1
Hex value:
0x04C11DB7