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2: Programmer's Model
2.2
Memory formats
The ARM720T processor views memory as a linear collection of bytes numbered upwards from
zero, as follows:
Bytes 0 to 3
Bytes 4 to 7
Bytes 8 to 11
Words are stored in memory as big or little-endian, as described in the following sections:
Big-endian format
•
Little-endian format
•
The endianness used depends on the status of the B bit in the Control Register of the system
control coprocessor. See
2.2.1
Big-endian format
In big-endian format, the most significant byte of a word is stored at the lowest numbered byte
and the least significant byte at the highest numbered byte. Byte 0 of the memory system is
therefore connected to data lines 31 to 24.
Big-endian format is shown in Figure 2-1.
Note:
•
Most significant byte is at lowest address
•
Word is addressed by byte address of most significant byte.
2-2
Hold the first stored word.
Hold the second stored word.
Hold the third stored word.
on page 2-3.
Control Register
31
24 23
Higher address
8
4
0
Lower address
Figure 2-1 Big-endian addresses of bytes with words
on page 3-4 for more information.
16 15
8 7
9
10
11
5
6
7
1
2
3
EPSON
Word
0
address
8
4
0
ARM720T CORE CPU MANUAL
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