Section 2 MCU Operating Modes and Address Space
2.1 Overview
The H8/532 microcomputer unit (MCU) operates in five modes numbered 1, 2, 3, 4, and 7. The
mode is selected by the inputs at the mode pins (MD2 to MD0) at the instant when the chip comes
out of a reset. As indicated in table 2-1, the MCU mode determines the size of the address space,
the usage of on-chip ROM, and the operating mode of the CPU. The MCU mode also affects the
functions of I/O pins.
Table 2-1 Operating Modes
MD2 MD1 MD0 MCU Mode Address Space On-Chip ROM CPU Mode
000 — — — —
0 0 1 Mode 1 Expanded minimum Disabled Minimum mode
0 1 0 Mode 2 Expanded minimum Enabled Minimum mode
0 1 1 Mode 3 Expanded maximum Disabled Maximum mode
1 0 0 Mode 4 Expanded maximum Enabled Maximum mode
101 — — — —
110 — — — —
1 1 1 Mode 7 Single-chip only Enabled Minimum mode
Notation: 0: Low level
1: High level
—: Cannot be used
Modes 1 to 4 are referred to as “expanded” because they permit access to off-chip memory and
peripheral addresses. The expanded minimum modes (modes 1 and 2) support a maximum
address space of 64K bytes. The expanded maximum modes (modes 3 and 4) support a maximum
address space of 1M byte.
Interrupt service is slightly slower in the expanded maximum modes than in the other modes
because the CPU has to save its code page register.
The H8/532 cannot be set to modes 0, 5, and 6. The mode pins should never be set to these
values.
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