Epson ARM720T Manuel D’Utilisation
2: Programmer’s Model
ARM720T CORE CPU MANUAL
EPSON
2-3
2.2.2
Little-endian format
In little-endian format, the lowest numbered byte in a word is considered the least significant
byte of the word, and the highest numbered byte the most significant. Byte 0 of the memory
system is therefore connected to data lines 7 to 0.
Little-endian format is shown in Figure 2-2.
Little-endian format is shown in Figure 2-2.
Figure 2-2 Little-endian addresses of bytes with words
Note:
•
Least significant byte is at lowest address
•
Word is addressed by byte address of least significant byte.
2.3
Instruction length
Instructions are:
•
32 bits long in ARM state
•
16 bits long in Thumb state.
2.4
Data types
The ARM720T processor supports the following data types:
•
byte (8-bit)
•
halfword (16-bit)
•
word (32-bit).
You must align these as follows:
•
word quantities to 4-byte boundaries
•
halfwords quantities to 2-byte boundaries
•
byte quantities can be placed on any byte boundary.
Higher address
8
4
0
31
24
23
Word
address
16
15
8
7
0
Lower address
7
10
6
9
5
8
4
11
3
2
1
0