PM0056 datasheet(30/156 Pages) STMICROELECTRONICS

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The Cortex-M3 processor

PM0056

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DocID15491 Rev 5

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 zero

•

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 on page 26 describes the behavior of direct byte, halfword,

or word accesses to the bit-band regions.

2.2.6

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

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. See Figure 11

for an example.

Figure 11. Little-endian example

Memory

Address A

A+1

lsbyte

msbyte

A+2

A+3

24 23

16 15

8 7

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