Atmel SAM4S-XPLD Atmel ATSAM4S-XPLD ATSAM4S-XPLD Hoja De Datos

 66

SAM4S [DATASHEET]

11100E–ATARM–24-Jul-13

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-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. Writing
0x00 has the same effect as writing 0x0E.

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

 describes the behavior of direct byte, halfword, or word accesses to the bit-band

regions.

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.

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