Little Endian

[admin]

Hello All,

              Are  all  freescale microcontrollers  big endian ? If they are like that ,why is it so? Any advantage?

Message Edited by 1#thunderbolt on 2009-01-22 09:21 AM

[Sara111]

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[StephenRussell]

Yes, processor architectures designed by Motorola and Freescale are big endian, but it isn't that simple now, see below.

When the 6800 and 68000 were originally designed, it was believed that big endian architecture was better for communications applications.  As the families evolved over the years they stayed big endian for compatibility.

However Freescale now manufactures processors with architectures originally designed by others, such as IBM and ARM.  These follow their own path.

Many of the high-performance architectures today provide for switching endianess under program control.  Some operating systems attempt to support this, but in practice few applications use this feature.

For further discussion see:

http://www.ietf.org/rfc/ien/ien137.txt

http://en.wikipedia.org/wiki/Endianness

For how to deal with endianess in C see:

http://www.ibm.com/developerworks/aix/library/au-endianc/index.html?ca=drs-

      Steve

[Lundin]

Interesting essay there

One thing people often overlook in the endian debate is the utterly common checksum algorithm known as CRC. This algorithm is present in almost every data communication protocol made during the last 30 years. It is generally considered to be a good algorithm for error detection.

It has one problem however, and that is execution time. It takes quite some time to go through the whole data protocol and check it with the bitwise XOR. To solve this, you could put the whole CRC calculation in hardware. This is rather easily achieved on any serial bus with a clock, you just need some digital logic XOR gates. In order for this to work, the checksum must be stored according to big endian.

This is one reason why big endian should be used, which is based on practical useage rather than "religious belief".