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Architecture
16
2.4 Data Formats and Addressing
This section explains how data is organized in R3900 registers and memory.
The R3900 uses the following data formats: 64-bit doubleword, 32-bit word, 16-bit halfword and 8-bit byte.
The byte order can be set to either big endian or little endian.
Figure 2-5 shows how bytes are ordered in words, and how words are ordered in multiple words, for both the
big-endian and little-endian formats.
31
24
23 16 15 8 7
0
Word address
8 9 10 11 8
4 5 6 7 4
0 1 2 3 0
 Byte 0 is the most significant byte (bit 31-24).
 A word is addressed beginning with the most significant byte.
(a) Big endian
31
24
23
16
15
8
7
0
Word address
11 10 9 8 8
7 6 5 4 4
3 2 1 0 0
 Byte 0 is the least significant byte (bit 7-0).
 A word is addressed beginning with the least significant byte.
(b) Little endian
Higher address
Lower address
Higher address
Lower address
Figure 2-5. Big endian and little endian formats