3069RF-ZTAT Datasheet, PDF (138/1003 Pages) Renesas Technology Corp – RENESAS 16-BIT SINGLE-CHIP MICROCOMPUTER

6.2 Register Descriptions
6.2.1 Bus Width Control Register (ABWCR)
ABWCR is an 8-bit readable/writable register that selects 8-bit or 16-bit access for each area.
Bit
7
Modes
1, 3, 5,
and 7
ABW7
Initial value 1
Read/Write R/W
Modes Initial value 0
2 and 4 _{Read/Write R/W}
6
ABW6
1
R/W
0
R/W
5
ABW5
1
R/W
0
R/W
4
ABW4
1
R/W
0
R/W
3
ABW3
1
R/W
0
R/W
2
ABW2
1
R/W
0
R/W
1
ABW1
1
R/W
0
R/W
0
ABW0
1
R/W
0
R/W
When ABWCR contains H'FF (selecting 8-bit access for all areas), the chip operates in 8-bit bus
mode: the upper data bus (D₁₅ to D₈) is valid, and port 4 is an input/output port. When at least one
bit is cleared to 0 in ABWCR, the chip operates in 16-bit bus mode with a 16-bit data bus (D₁₅ to
D₀). In modes 1, 3, 5, and 7, ABWCR is initialized to H'FF by a reset and in hardware standby
mode. In modes 2 and 4, ABWCR is initialized to H'00 by a reset and in hardware standby mode.
It is not initialized in software standby mode.
Bits 7 to 0—Area 7 to 0 Bus Width Control (ABW7 to ABW0): These bits select 8-bit access
or 16-bit access for the corresponding areas.
Bits 7 to 0
ABW7 to ABW0
0
1
Description
Areas 7 to 0 are 16-bit access areas
Areas 7 to 0 are 8-bit access areas
ABWCR specifies the data bus width of external memory areas. The data bus width of on-chip
memory and registers is fixed, and does not depend on ABWCR settings. These settings are
therefore meaningless in the single-chip modes (mode 7).
Rev. 5.0, 09/04, page 116 of 978