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3.8 Standby Mode (Low Power Consumption)
3.8.3
Stop Mode
This section describes the operations in stop mode.
I
Operations in Stop Mode
H
Transition to the stop mode
The stop mode is a mode which stops the oscillation. Contents of the registers and RAM just
before transition to the stop mode are retained and most functions are stopped.
In main clock mode, the main clock stops the oscillation, but the subclock continues the
oscillation. Thus, though the count operation of the watch prescaler and part of the functions
operating on the subclock continue their operations, other peripheral functions and CPU,
excluding the external interrupt circuits, stop operations.
In subclock mode, both the main clock and subclock stop oscillation, and all functions other than
the external interrupt circuits stop their functions. Thus, data can be retained with minimum
power consumption.
A transition to the stop mode is caused by writing "1" into the stop bit (STBC: STP) of the
standby control register. At this time, if the pin state designate bit (STBC: SPL) is "0", the states
of external pins are retained. If the bit is "1", external pins are put into high impedance.
If an interrupt request has occurred when "1" is written into the STP bit, the write operation is
ignored and execution of instructions continues without making a transition to the stop mode
(No transition to the stop mode occurs even after interrupt processing is completed).
To make a transition to the stop mode in the main clock mode, prohibit (TBTC: TBIE=0) the
interrupt request output of the timebase timer if necessary. Likewise, to make a transition to the
stop mode in subclock mode, prohibit (WPCR: WIE=0) the watch interrupt request output of the
watch prescaler.
H
Stop mode release
The stop mode can be released by a reset or external interrupt.
If a reset occurs in stop mode, the reset operation is performed after taking the oscillation
stabilization wait time of the main clock.
Pin states are initialized by the reset.
If an interrupt request whose interrupt level is higher than "11" comes from an external interrupt
circuit in stop mode, the stop mode is released regardless of the interrupt enable flag (CCR: I)
and interrupt level bits (CCR: IL1, 0) of CPU. Since peripheral functions are stopped in stop
mode, no interrupt requests other than external interrupts occur. Though the watch prescaler
operates in main stop mode, no watch interrupts occur.
If the stop mode is released, a normal interrupt operation is performed following the passage of
the oscillation stabilization wait time. If the interrupt is accepted, interrupt processing is
performed. If the interrupt is not accepted, execution starts with the instruction following the
instruction executed just before transition to the stop mode.
If the stop mode is released by an external interrupt, part of the peripheral functions restarts
halfway through their operations. Thus, for example, the first interval time of the interval timer
function is undefined. Each peripheral function should be initialized after returning from the stop
mode.