Section 3 Mcu Operating Modes; Overview; Operating Mode Selection; Mcu Operating Modes - Hitachi H8S/2646 Hardware Manual

3.1

Overview

3.1.1

Operating Mode Selection

The H8S/2646 Series has four operating modes (modes 4 to 7). These modes enable selection of
the CPU operating mode, enabling/disabling of on-chip ROM, and the initial bus width setting, by
setting the mode pins (MD2 to MD0).
Table 3-1 lists the MCU operating modes.
Table 3-1 MCU Operating Mode Selection
MCU
Operating
Mode MD2 MD1 MD0
0* 0 0
1*
2* 1
3*
4 1 0
5
6 1
7
Note: * Not available in the H8S/2646 Series.
The CPU's architecture allows for 4 Gbytes of address space, but the H8S/2646 Series actually
accesses a maximum of 16 Mbytes.
Modes 4 to 6 are externally expanded modes that allow access to external memory and peripheral
devices.
The external expansion 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.
Note that the functions of each pin depend on the operating mode.

Section 3 MCU Operating Modes

CPU
Operating
Mode
0 —
1 —
0
1
0 Advanced On-chip ROM disabled,
1
0
1
Description
—
expanded mode
On-chip ROM enabled,
expanded mode
Single-chip mode
External Data Bus
On-Chip Initial Max.
ROM Width Width
— — —
Disabled 16 bits 16 bits
8 bits 16 bits
Enabled 8 bits 16 bits
— —
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