PM0214 datasheet(32/245 Pages) STMICROELECTRONICS

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The Cortex-M4 processor

PM0214

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DocID022708 Rev 4

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 9 on page 32 shows examples of bit-band mapping between the SRAM bit-band

alias region and the SRAM bit-band region:

•

The alias word at 0x23FFFFED maps to bit[0] of the bit-band byte at

0x200FFFFF: 0x23FFFFED = 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).

Figure 9. Bit-band mapping

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.

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