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UM10360_0
© NXP B.V. 2009. All rights reserved.
User manual
Rev. 00.06 — 5 June 2009
711 of 808
NXP Semiconductors
UM10360
Chapter 34: Appendix: Cortex-M3 User Guide
•
The alias word at
0x23FFFFFC
maps to bit[7] of the bit-band byte at
0x200FFFFF
:
0x23FFFFFC
=
0x22000000
+ (
0xFFFFF
*32) + (7*4).
•
The alias word at
0x22000000
maps to bit[0] of the bit-band byte at
0x20000000
:
0x22000000
=
0x22000000
+ (0*32) + (0 *4).
•
The alias word at
0x2200001C
maps to bit[7] of the bit-band byte at
0x20000000
:
0x2200001C
=
0x22000000
+ (0*32) + (7*4).
3.2.5.1
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
3.2.5.2
Directly accessing a bit-band region
describes the behavior of direct byte, halfword, or word accesses to the
bit-band regions.
Fig 143. Bit-band mapping
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