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7.2
Register Descriptions
7.2.1
Bus Width Control Register (ABWCR)
Bit
:
Modes 5 to 7
Initial value :
RW
:
Mode 4
Initial value :
RW
:
ABWCR is an 8-bit readable/writable register that designates each area for either 8-bit access or
16-bit access.
ABWCR sets the data bus width for the external memory space. The bus width for on-chip
memory and internal I/O registers is fixed regardless of the settings in ABWCR.
In normal mode, the settings of bits ABW7 to ABW1 have no effect on operation.
After a power-on reset and in hardware standby mode, ABWCR is initialized to H'FF in modes 5
to 7, and to H'00 in mode 4. It is not initialized by a manual reset or in software standby mode.
Bits 7 to 0—Area 7 to 0 Bus Width Control (ABW7 to ABW0): These bits select whether the
corresponding area is to be designated for 8-bit access or 16-bit access.
Bit n
ABWn
Description
0
Area n is designated for 16-bit access
1
Area n is designated for 8-bit access
136
7
6
ABW7
ABW6
1
1
R/W
R/W
0
0
R/W
R/W
5
4
ABW5
ABW4
1
1
R/W
R/W
0
0
R/W
R/W
3
2
ABW3
ABW2
1
1
R/W
R/W
0
0
R/W
R/W
1
0
ABW1
ABW0
1
1
R/W
R/W
0
0
R/W
R/W
(n = 7 to 0)
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