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Section 5 Power-Down Modes
5.1
Overview
The H8/3937 Series and H8/3937R Series have nine modes of operation after a reset. These
include eight power-down modes, in which power dissipation is significantly reduced. Table 5-1
gives a summary of the eight operating modes.
Table 5-1
Operating Modes
Operating Mode
Description
Active (high-speed) mode
The CPU and all on-chip peripheral functions are operable on the
system clock in high-speed operation. The FLEX decoder is
independently operable on the subclock.
Active (medium-speed) mode
The CPU and all on-chip peripheral functions are operable on the
system clock in low-speed operation. The FLEX decoder is
independently operable on the subclock.
Subactive mode
The CPU is operable on the subclock in low-speed operation. The
FLEX decoder is independently operable on the subclock.
Sleep (high-speed) mode
The CPU halts. On-chip peripheral functions are operable on the
system clock. The FLEX decoder is independently operable on
the subclock.
Sleep (medium-speed) mode
The CPU halts. On-chip peripheral functions operate at a
frequency of 1/64, 1/32, 1/16, or 1/8 of the system clock frequency.
The FLEX decoder is independently operable on the subclock.
Subsleep mode
The CPU halts. Timer A, timer C, timer G, timer F, the WDT, SCI1,
SCI31, SCI32, and the FLEX decoder are operable on the
subclock.
Watch mode
The timer A time-base function, timer F, timer G, and the FLEX
decoder are operable on the subclock.
Standby mode
The CPU and all on-chip peripheral functions halt. The FLEX
decoder is independently operable on the subclock.
Module standby mode
Individual on-chip peripheral functions specified by software enter
standby mode and halt.
Of these nine operating modes, all but the active (high-speed) mode are power-down modes. In
this section the two active modes (high-speed and medium speed) will be referred to collectively
as active mode.
Figure 5-1 shows the transitions among these operation modes. Table 5-2 indicates the internal
states in each mode.