Datasheet

SAM4E [DATASHEET]

Atmel-11157D-ATARM-SAM4E16-SAM4E8-Datasheet_12-Jun-14

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-

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

Directly Accessing a Bit-band Region

“Behavior of Memory Accesses” 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. “Little-endian Format”

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

0x23FFFFE00x23FFFFE80x23FFFFEC0x23FFFFF00x23FFFFF40x23FFFFF80x23FFFFFC

0x220000000x220000140x220000180x2200001C 0x220000080x22000010 0x2200000C

32 MB alias region

7 0

0x200000000x200000010x200000020x20000003

6 5 4 3 2 1 07 6 5 4 3 2 1 7 6 5 4 3 2 1 07 6 5 4 3 2 1

07 6 5 4 3 2 1 6 5 4 3 2 107 6 5 4 3 2 1 07 6 5 4 3 2 1

0x200FFFFC0x200FFFFD0x200FFFFE0x200FFFFF

1 MB SRAM bit-band region