2. ARM Cortex-M4 core access privileges also includes
accesses via the debug interface.
4.2.1 Aliased bit-band regions
The SRAM_U, AIPS-Lite, and general purpose input/output (GPIO) module resources
reside in the Cortex-M4 processor bit-band regions.
The processor also includes two 32 MB aliased bit-band regions associated with the two
1 MB bit-band spaces. Each 32-bit location in the 32 MB space maps to an individual bit
in the bit-band region. A 32-bit write in the alias region has the same effect as a read-
modify-write operation on the targeted bit in the bit-band region.
Bit 0 of the value written to the alias region determines what value is written to the target
bit:
• Writing a value with bit 0 set writes a 1 to the target bit.
• Writing a value with bit 0 clear writes a 0 to the target bit.
A 32-bit read in the alias region returns either:
• a value of 0x0000_0000 to indicate the target bit is clear
• a value of 0x0000_0001 to indicate the target bit is set
31
0 0
31
Bit-band region Alias bit-band region
1 MByte
32 MByte
Figure 4-1. Alias bit-band mapping
Chapter 4 Memory Map
K22F Sub-Family Reference Manual, Rev. 4, 08/2016
NXP Semiconductors 141
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