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2.7
CPU States
2.7.1
Overview
There are four CPU states: the reset state, program execution state, program halt state, and
exception-handling state. The program execution state includes active (high-speed or medium-
speed) mode and subactive mode. In the program halt state there are a sleep (high-speed or
medium-speed) mode, standby mode, watch mode, and sub-sleep mode. These states are shown in
figure 2.14. Figure 2.15 shows the state transitions.
CPU state
Note: See section 5, Power-Down Modes, for details on the modes and their transitions.
Reset state
The CPU is initialized
Program
execution state
Program halt state
A state in which some
or all of the chip
functions are stopped
to conserve power
Exception-
handling state
A transient state in which the CPU changes
the processing flow due to a reset or an interrupt
Figure 2.14 CPU Operation States
Active
(high speed) mode
The CPU executes successive program
instructions at high speed,
synchronized by the system clock
Active
(medium speed) mode
The CPU executes successive
program instructions at
reduced speed, synchronized
by the system clock
Subactive mode
The CPU executes
successive program
instructions at reduced
speed, synchronized
by the subclock
Sleep (high-speed)
mode
Sleep (medium-speed)
mode
Standby mode
Watch mode
Subsleep mode
Low-power
modes
45
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