Atmel ARM-Based Evaluation Kit for SAM4S16C, 32-Bit ARM® Cortex® Microcontroller ATSAM4S-WPIR-RD ATSAM4S-WPIR-RD Data Sheet
Product codes
ATSAM4S-WPIR-RD
SAM4S Series [DATASHEET]
Atmel-11100G-ATARM-SAM4S-Datasheet_27-May-14
74
Figure 12-4.
Bit-band Mapping
Directly Accessing an Alias Region
Writing to a word in the alias region updates a single bit in the bit-band region.
Bit[0] of the value written to a word in the alias region determines the value written to the targeted bit in the bit-
Bit[0] of the value written to a word in the alias region determines the value written to the targeted bit in the bit-
band region. Writing a value with bit[0] set to 1 writes a 1 to the bit-band bit, and writing a value with bit[0] set to 0
writes a 0 to the bit-band bit.
Bits[31:1] of the alias word have no effect on the bit-band bit. Writing 0x01 has the same effect as writing 0xFF.
Bits[31:1] of the alias word have no effect on the bit-band bit. Writing 0x01 has the same effect as writing 0xFF.
Writing 0x00 has the same effect as writing 0x0E.
Reading a word in the alias region:
Reading a word in the alias region:
0x00000000 indicates that the targeted bit in the bit-band region is set to 0
0x00000001 indicates that the targeted bit in the bit-band region is set to 1
Directly Accessing a Bit-band Region
describes the behavior of direct byte, halfword, or word accesses to the bit-band
regions.
12.4.2.6 Memory Endianness
The processor views memory as a linear collection of bytes numbered in ascending order from zero. For example,
bytes 0–3 hold the first stored word, and bytes 4–7 hold the second stored word.
describes
how words of data are stored in memory.
Little-endian Format
In little-endian format, the processor stores the least significant byte of a word at the lowest-numbered byte, and
the most significant byte at the highest-numbered byte. For example:
0x23FFFFE4
0x22000004
0x23FFFFE0
0x23FFFFE8
0x23FFFFEC
0x23FFFFF0
0x23FFFFF4
0x23FFFFF8
0x23FFFFFC
0x22000000
0x22000014
0x22000018
0x2200001C
0x22000008
0x22000010
0x2200000C
32 MB alias region
0
7
0
0
7
0x20000000
0x20000001
0x20000002
0x20000003
6
5
4
3
2
1
0
7
6
5
4
3
2
1
7
6
5
4
3
2
1
0
7
6
5
4
3
2
1
0
7
6
5
4
3
2
1
6
5
4
3
2
1
0
7
6
5
4
3
2
1
0
7
6
5
4
3
2
1
0x200FFFFC
0x200FFFFD
0x200FFFFE
0x200FFFFF
1 MB SRAM bit-band region