LM3S8G62 Datasheet, PDF (80/1096 Pages) Texas Instruments – Stellaris® LM3S8G62 Microcontroller

OBSOLETE: TI has discontinued production of this device.
The Cortex-M3 Processor
2.4.5
Bit-Banding
A bit-band region maps each word in a bit-band alias region to a single bit in the bit-band region.
The bit-band regions occupy the lowest 1 MB of the SRAM and peripheral memory regions. Accesses
to the 32-MB SRAM alias region map to the 1-MB SRAM bit-band region, as shown in Table
2-6 on page 80. Accesses to the 32-MB peripheral alias region map to the 1-MB peripheral bit-band
region, as shown in Table 2-7 on page 80. For the specific address range of the bit-band regions,
see Table 2-4 on page 75.
Note: A word access to the SRAM or the peripheral bit-band alias region maps to a single bit in
the SRAM or peripheral bit-band region.
A word access to a bit band address results in a word access to the underlying memory,
and similarly for halfword and byte accesses. This allows bit band accesses to match the
access requirements of the underlying peripheral.
Table 2-6. SRAM Memory Bit-Banding Regions
Address Range
Start
0x2000.0000
End
0x2000.FFFF
0x2200.0000
0x221F.FFFF
Memory Region
Instruction and Data Accesses
SRAM bit-band region Direct accesses to this memory range behave as SRAM
memory accesses, but this region is also bit addressable
through bit-band alias.
SRAM bit-band alias Data accesses to this region are remapped to bit band
region. A write operation is performed as
read-modify-write. Instruction accesses are not remapped.
Table 2-7. Peripheral Memory Bit-Banding Regions
Address Range
Start
0x4000.0000
End
0x400F.FFFF
0x4200.0000
0x43FF.FFFF
Memory Region
Instruction and Data Accesses
Peripheral bit-band
region
Direct accesses to this memory range behave as
peripheral memory accesses, but this region is also bit
addressable through bit-band alias.
Peripheral bit-band alias Data accesses to this region are remapped to bit band
region. A write operation is performed as
read-modify-write. Instruction accesses are not permitted.
The following formula shows how the alias region maps onto the bit-band region:
bit_word_offset = (byte_offset x 32) + (bit_number x 4)
bit_word_addr = bit_band_base + bit_word_offset
where:
bit_word_offset
The position of the target bit in the bit-band memory region.
bit_word_addr
The address of the word in the alias memory region that maps to the targeted bit.
bit_band_base
The starting address of the alias region.
80
July 24, 2012
Texas Instruments-Production Data