HD6413007F20 Datasheet, PDF (142/798 Pages) Renesas Technology Corp – Hardware Manual Renesas 16-Bit Single-Chip Microcomputer H8 Family/H8/300H Series

6. Bus Controller
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
Modes
1 and 3
Modes
2 and 4
7
ABW7
Initial value 1
Read/Write R/W
Initial value 0
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 and 3, 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.
Rev.5.00 Sep. 12, 2007 Page 112 of 764
REJ09B0396-0500