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CHAPTER 3 CPU
3.7
Standby Modes (Low-Power Consumption)
The standby modes consist of sleep mode, stop mode, and watch mode.
From both main and subclock clock modes, standby modes are changed to sleep
mode, stop mode, or watch mode by setting the standby control register (STBC).
From main clock mode, you can go only to sleep or stop mode, but from subclock
mode you can go any of the three standby modes. Standby mode reduces the power
consumption by stopping the operation of the CPU and peripheral functions.
This section describes the relationship between standby mode and clock mode, and
the operation of various sections during standby.
s Standby Modes
Watch mode reduce the power consumption by lowering the frequencies of the clocks that run
the CPU and peripheral circuits. You can do this by switching from main clock to subclock
mode, or by using the speed-shift function to select a lower main clock frequency. Standby
mode reduce the power consumption, however, by stopping the clock signal supply to the CPU
via clock controller (sleep mode), by stopping the clock signal supply to the CPU and peripheral
circuits (watch mode), or by stopping the source oscillator itself (stop mode).
r Main-sleep Mode
Main-sleep mode stops the CPU and watchdog timer, but operate the peripheral functions
except watch prescaler by the main clock. (Certain functions can still run on the subclock.)
r Sub-sleep Mode
Sub-sleep mode stops the main clock oscillator, CPU, watchdog timer, and timebase timer, but
operate the peripheral functions on the subclock.
r Main-stop Mode
Main-stop mode stops the CPU and peripheral functions. The main clock oscillator is stopped,
but the subclock oscillator keeps running. Everything is shut down except external interrupt
servicing, watch prescaler counter operation, and some functions that operate from the
subclock.
r Sub-stop Mode
Sub-stop mode stops all chip functions except the external interrupt, and stops the main clock
and subclock oscillations.
r Watch Mode
You can only go to watch mode from the subclock clock mode. All functions are shut down
except the watch prescaler (watch interrupt), external interrupts, and some functions that
operate from the subclock.
Even when the main clock is stopped, as it is in the main-stop a
Even when the main clock is stopped, as it is in the main-stop and watch modes, as long as
the subclock oscillation is still operating, LCD controller/drivers will still operate. See
CHAPTER 14 "LCD CONTROLLER/DRIVER" and the clock supply map provided in Section
3.6 "Clocks" for details.