Standby Modes (Low-Power Consumption) - Fujitsu F2MC-8L Series Hardware Manual

3.7

Standby Modes (Low-power Consumption)

The standby modes consist of sleep mode, stop mode, and watch mode.
Standby modes are changed to sleep mode or stop mode by setting the standby
control register (STBC).
The main clock mode enables transition to sleep or stop mode. The subclock mode
enables transition to sleep, stop or watch mode.
Standby mode reduces the power consumption by stopping the operation of the CPU
and peripheral functions.
This section describes the relationship between standby and clock modes and the
operating state of each module in each standby mode.
Standby Modes
In the clock mode, power consumption is reduced by lowering the operating clock speed for the
CPU and peripheral circuits, for example, by switching from the main clock to subclock or
lowering the main clock speed (using the clock gear function). In the standby mode, however,
power consumption is reduced by stopping clock signal supply to the CPU by the clock
controller (sleep mode), stopping clock signal supply to the CPU and peripherals (watch mode),
or by stopping clock oscillation (stop mode).
Main-sleep mode
Main-sleep mode stops operations of the CPU and watchdog timer while leaving the peripheral
functions, excluding the watch prescaler, operating with the main clock (some of which can
operate with the subclock).
Sub-sleep mode
Sub-sleep mode stops oscillation of the main clock and operations of the CPU, watchdog timer,
and of timebase timer, with peripheral functions operating with the subclock.
Main-stop mode
Main-stop mode stops operations of the CPU and peripheral functions, with the main clock
stopping oscillation but the subclock oscillating. This mode stops all the functions, except the
external interrupt, counting operation of the watch prescaler, and some subclock-based
functions.
Sub-stop mode
Sub-stop mode stops all functions except the external interrupt, where both of the main clock
and subclock stop oscillation.
Watch mode
The CPU can enter watch mode only when it is in subclock mode. This mode stops all the
functions, except the watch prescaler (watch interrupt), external interrupt circuit, and some
subclock-based functions.
Reference:
Even when the main clock is being stopped, for example, in main-stop or watch mode, some
3.7 Standby Modes (Low-power Consumption)
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