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Appendix A: Little and Big Endians

The “end” in “endians” refers to the address of the most significant or least significant

byte in a multiple-byte data type (such as short, long or float). The address of big endians

is the most significant byte (the “big” end) while the address of little endians is the least

significant byte (the “little” end).

Example using standard C conventions:

long lType;

short sType[2]

char cType[5] = “ABCD”;

lType = 0x12345678;

sType[1] = 0x1234 ;

sType[2] = 0x5678 ;

Memory structure: big endians (starts with MSB):

00 08

12 34 56 78 - lType

12 34 56 78 - sType

AB CD 0 - cType

Memory structure: little endians (starts with LSB):

00 08

78 56 34 12 - lType

34 12 78 56 - sType

AB CD 0 - cType

The CANopen protocol supports the little endian method; for example, a node replies to

a TPDO with three objects:

Object 1: Signed24 - 0x12ABCD

Object 2: Unsigned32 - 0x123456AB

Object 3: Unsigned8 - 0x1F

The CAN octet will be as follows:

CD AB 12 AB 56 34 12 1F

CANopen DS 301 Implementation Guide Initial CAN Communication Setup

MAN-CAN301IG (Ver. 2.1)

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Elmomc CANopen DS 301 Implementation Guide Manual do Utilizador Página 118