65
11100B–ATARM–31-Jul-12
SAM4S Series [Preliminary]
•
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.
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 =
0x22 (0xFFFFF*32) + (0*4).
• The alias word at 0x23FFFFFC maps to bit[7] of the bit-band byte at 0x200FFFFF: 0x23FFFFFC =
0x22 (0xFFFFF*32) + (7*4).
• The alias word at 0x22000000 maps to bit[0] of the bit-band byte at 0x20000000: 0x22000000 =
0x22 (0*32) + (0 *4).
• The alias word at 0x2200001C maps to bit[7] of the bit-band byte at 0x20000000: 0x2200001C =
0x2 (0*32) + (7*4).
Figure 11-4. 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 tar-
geted 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.
Reading a word in the alias region:
• 0x00000000 indicates that the targeted bit in the bit-band region is set to 0
• 0x00000001 indicates that the targeted bit in the bit-band region is set to 1
0x23FFFFE4
0x22000004
0x23FFFFE0
0x23FFFFE8
0x23FFFFEC
0x23FFFFF0
0x23FFFFF4
0x23FFFFF8
0x23FFFFFC
0x22000000
0x22000014
0x22000018
0x2200001C
0x22000008
0x22000010
0x2200000C
32 MB alias region
0
7
0
0
7
0x20000000
0x20000001
0x20000002
0x20000003
6
5
4
3
2
1
0
7
6
5
4
3
2
1
7
6
5
4
3
2
1
0
7
6
5
4
3
2
1
0
7
6
5
4
3
2
1
6
5
4
3
2
1
0
7
6
5
4
3
2
1
0
7
6
5
4
3
2
1
0x200FFFFC
0x200FFFFD
0x200FFFFE
0x200FFFFF
1 MB SRAM bit-band region
Содержание SAM4S Series
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Страница 1142: ...1142 11100B ATARM 31 Jul 12 SAM4S Series Preliminary Figure 43 3 100 ball VFBGA Package Drawing ...
Страница 1143: ...1143 11100B ATARM 31 Jul 12 SAM4S Series Preliminary Figure 43 4 64 lead LQFP Package Drawing ...
Страница 1145: ...1145 11100B ATARM 31 Jul 12 SAM4S Series Preliminary Figure 43 5 64 lead QFN Package Drawing ...