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.
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
