Datasheet

48
XMEGA A4U [DATASHEET]
Atmel-8387H-AVR-ATxmega16A4U-34A4U-64A4U-128A4U-Datasheet_09/2014
27. CRC – Cyclic Redundancy Check Generator
27.1 Features
z Cyclic redundancy check (CRC) generation and checking for
z Communication data
z Program or data in flash memory
z Data in SRAM and I/O memory space
z Integrated with flash memory, DMA controller and CPU
z Continuous CRC on data going through a DMA channel
z Automatic CRC of the complete or a selectable range of the flash memory
z CPU can load data to the CRC generator through the I/O interface
z CRC polynomial software selectable to
z CRC-16 (CRC-CCITT)
z CRC-32 (IEEE 802.3)
z Zero remainder detection
27.2 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).
z CRC-16:
z CRC-32:
Polynomial: x
16
+x
12
+x
5
+1
Hex value: 0x1021
Polynomial: x
32
+x
26
+x
23
+x
22
+x
16
+x
12
+x
11
+x
10
+x
8
+x
7
+x
5
+x
4
+x
2
+x+1
Hex value: 0x04C11DB7