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CHAPTER 4 CLOCK GENERATION FUNCTION
User’s Manual U15109EJ3V0UD
125
4.4 Power Save Functions
4.4.1 General
This product provides the following power saving functions.
These modes can be combined and switched to suit the target application, thus enabling the effective
implementation of low-power systems.
(1) HALT mode
In this mode, the clock oscillator continues to operate but the CPU operating clock is stopped. A clock continues
to be supplied for other on-chip peripheral functions to maintain the operation of those functions. This enables
the system’s total power consumption to be reduced.
A special-purpose instruction (the HALT instruction) is used to switch to HALT mode.
(2) IDLE mode
This mode stops the entire system by stopping the CPU operating clock as well as the operating clock for on-chip
peripheral functions while the clock oscillator is still operating. However, the subclock continues to operate and
supplies a clock to the on-chip peripheral functions.
When this mode is canceled, there is no need for the oscillator to wait for the oscillation stabilization time, so
normal operation can be resumed quickly.
When the IDLE bit in the power save control register (PSC) is set (1), the system switches to IDLE mode.
(3) Software STOP mode
This mode stops the entire system by stopping the main clock oscillators. The subclock continues to be supplied
to keep on-chip peripheral functions operating. If the subclock is not used, ultra-low-power-consumption mode
(leak current only) is set. STOP mode setting is prohibited if the CPU is operating via the subclock.
If the STP bit of the PSC register is set (1), the system enters STOP mode.
(4) Subclock operation
In this mode, the CPU clock is set to operate using the subclock and the MCK bit of the PCC register is set (1) to
set low-power-consumption mode in which the entire system operates using only the subclock.
When HALT mode has been set, the CPU operating clock is stopped so that power consumption can be
reduced.
When IDLE mode has been set, the CPU operating clock and some peripheral functions (DMAC and BCU) are
stopped to enable an even greater reduction in power consumption than when in HALT mode.