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CHAPTER 3 CPU
3.7.3
Stop Mode
This section describes the operations of stop mode.
I Operation of stop mode
G Changing to stop mode
Stop mode stops the source oscillation. Most functions stop while maintaining all register and RAM
contents at their value immediately before changing to stop mode.
If the system is in main clock mode, the main clock oscillation stops. Except the external interrupt circuit,
however, the CPU and other peripheral functions stop operating.
Writing "1" to the stop bit in the standby control register (STBC: STP) changes the CPU to stop mode. At
this time, external pin states are held if the pin state specification bit (STBC: SPL) is "0". If SPL is "1",
external pins go to the high-impedance state. (Pins with the pull-up resistor go to the "H" level.)
If an interrupt request is generated when "1" is written to the STP bit, the write to the bit is ignored, and the
CPU continues the instruction execution without change to stop mode. (The CPU does not assume stop
mode even after completion of the interrupt processing.)
Prohibit interrupt request out from the timebase timer (TBTC: TBIE = "0") before changing to stop mode in
main clock mode as necessary. Similarly, prohibit watch prescaler interrupt request output from the watch
prescaler (WPCR: WIE = 0) before changing to stop mode in subclock mode.
G Wake-up from stop mode
A reset and an external interrupt wakes up the CPU from stop mode.
If reset occurs during stop mode on a product, the reset operation starts after the main clock oscillation
stabilization wait time. The reset initializes pin states.
If an interrupt request with an interrupt level higher than "11" occurs from an external interrupt circuit
during stop mode, the CPU wakes up from stop mode, regardless of the interrupt enable flag (CCR: I) and
interrupt level bits (CCR: IL1, IL0) in the CPU. Only external interrupt requests can occur during stop
mode because peripheral functions are stopped.
After wake-up from stop mode, the normal interrupt operation is performed after the oscillation
stabilization wait time has passed. If the interrupt request is accepted, the CPU executes interrupt
processing. If the interrupt request is not accepted, the CPU continues execution from the subsequent
instruction following the instruction executed immediately before entering stop mode.
Some peripheral functions restart from mid-operation when the CPU wakes up from stop mode by an
external interrupt. The first interval time from the interval timer function, for example, is indeterminate.
Therefore, initialize all peripheral functions after wake-up from stop mode.
Precaution:
Only interrupt requests from external interrupt circuits can be used to wake up from stop mode by an
interrupt.