Samsung S3C2440A - Manual (Page 43)

PROGRAMMER'S MODEL S3C2440A RISC MICROPROCESSOR
2-2
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
through 24.
31
8
4
0
23
9
5
1
10
6
2
11
7
3
8 7 0
4
0
8
Higher Address
Lower Address
Word Address
Most significant byte is at lowest address.
Word is addressed by byte address of most significant byte.
24 15 16
Figure 2-1. Big-Endian Addresses of Bytes within Words
LITTLE-ENDIAN FORMAT
In Little-Endian format, the lowest numbered byte in a word is considered the word's least significant byte, and the
highest numbered byte the most significant. Byte 0 of the memory system is therefore connected to data lines 7
through 0.
31 23 8 7 0
4
0
8
Higher Address
Lower Address
Word Address
Least significant byte is at lowest address.
Word is addressed by byte address of least significant byte.
24 15 16
8
4
0
9
5
1
10
6
2
11
7
3
Figure 2-2. Little-Endian Addresses of Bytes within Words
INSTRUCTION LENGTH
Instructions are either 32 bits long (in ARM state) or 16 bits long (in THUMB state).
Data Types
ARM920T supports byte (8-bit), halfword (16-bit) and word (32-bit) data types. Words must be aligned to four-byte
boundaries and half words to two-byte boundaries.