67
SAM4CP [DATASHEET]
43051E–ATPL–08/14
Notes: 1.
A word access to the SRAM or peripheral bit-band alias regions map to a single bit in the SRAM or
peripheral bit-band region.
Bit-band accesses can use byte, halfword, or word transfers. The bit-band transfer size matches the transfer
size of the instruction making the bit-band access.
2.
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
is the position of the target bit in the bit-band memory region.
Bit_word_addr
is the address of the word in the alias memory region that maps to the targeted bit.
Bit_band_base
is the starting address of the alias region.
Byte_offset
is the number of the byte in the bit-band region that contains the targeted bit.
Bit_number
is the bit position, 0-7, of the targeted bit.
Figure 12-4
shows examples of bit-band mapping between the SRAM bit-band alias region and the SRAM bit-band
region:
The alias word at 0x23FFFFE0 maps to bit [0] of the bit-band byte at 0x200FFFFF: 0x23FFFFE0 = 0x22000000 +
(0xFFFFF*32) + (0*4).
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).
Table 12-7.
Peripheral Memory Bit-banding Regions
Address Range
Memory Region
Instruction and Data Accesses
0x40000000 - 0x400FFFFF
Peripheral bit-band alias
Direct accesses to this memory range behave as
peripheral memory accesses, but this region is also bit-
addressable through bit-band alias.
0x42000000 - 0x43FFFFFF
Peripheral bit-band region
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.