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Table 2.2
MCU Operating Mode Selection* (ROMless and Mask ROM Versions)
MCU
Operating
Mode
MD2
0
0
1
2
3
4
1
5
6
7
Note: * Only modes 1 and 2 are available in the ROMless version.
The CPU's architecture allows for 4 gigabytes of address space, but the H8S/2678 Series chip
actually accesses a maximum of 16 Mbytes.
Modes 1, 2, and 4 to 6 are externally expanded modes that allow access to external memory and
peripheral devices.
The externally expanded modes allow switching between 8-bit and 16-bit bus modes. After
program execution starts, an 8-bit or 16-bit address space can be set for each area, depending on
the bus controller setting. If 16-bit access is selected for any one area, 16-bit bus mode is set; if 8-
bit access is selected for all areas, 8-bit bus mode is set. Pin functions depend on the operating
mode.
In the single-chip activation externally expanded mode, it is possible to switch between externally
expanded mode and single-chip mode. Immediately after a reset, the chip starts up in single-chip
mode, but after the start of program execution, it is possible to change to externally expanded
mode by setting the EXPE bit in the system control register (SYSCR) accordingly. Pin functions
depend on the operating mode.
32
CPU
Operating
MD1
MD0
Mode
0
0
—
1
Advanced
1
0
1
—
0
0
Advanced
1
1
0
1
On-Chip
Description
ROM
—
—
Expanded mode
Disabled 16 bits
with on-chip
ROM disabled
—
—
Expanded mode
Enabled
with on-chip
ROM enabled
External ROM
activation
expanded mode
with on-chip
ROM enabled
Single-chip
activation mode
with on-chip
ROM enabled
External Data
Bus
Initial
Max.
Width
Width
—
—
16 bits
8 bits
16 bits
—
—
8 bits
16 bits
16 bits
16 bits
8 bits
16 bits
—
16 bits
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