Atmel SAM4S-XPLD Atmel ATSAM4S-XPLD ATSAM4S-XPLD Hoja De Datos

 65

SAM4S [DATASHEET]

11100E–ATARM–24-Jul-13

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Accesses to the 32 MB peripheral alias region map to the 1 MB peripheral bit-band region, as shown in 

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Notes: 1.

A word access to the SRAM or peripheral bit-band alias regions map to a single bit in the SRAM or periph-
eral bit-band region.

2.

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.

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:

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Bit_word_offset

 is the position of the target bit in the bit-band memory region.

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Bit_word_addr

 is the address of the word in the alias memory region that maps to the targeted bit.

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Bit_band_base

 is the starting address of the alias region.

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Byte_offset

 is the number of the byte in the bit-band region that contains the targeted bit.

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Bit_number

 is the bit position, 0-7, of the targeted bit.

 shows examples of bit-band mapping between the SRAM bit-band alias region and the SRAM bit-band

region:

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The alias word at 0x23FFFFE0 maps to bit[0] of the bit-band byte at 0x200FFFFF: 0x23FFFFE0 = 0x22000000 + 
(0xFFFFF*32) + (0*4).

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The alias word at 0x23FFFFFC maps to bit[7] of the bit-band byte at 0x200FFFFF: 0x23FFFFFC = 0x22000000 + 
(0xFFFFF*32) + (7*4).

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The alias word at 0x22000000 maps to bit[0] of the bit-band byte at 0x20000000: 0x22000000 = 0x22000000 + (0*32) + (0 
*4).

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The alias word at 0x2200001C maps to bit[7] of the bit-band byte at 0x20000000: 0x2200001C = 0x22000000+ (0*32) + 
(7*4).

0x20000000-

0x200FFFFF 

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.

0x22000000-

0x23FFFFFF

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.

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.