STOP AND WAIT MODES
7902 Group User’s Manual
16-12
16.4 Wait mode
When the WIT instruction is executed, both of
φCPU and φBIU become inactive. (The oscillation does not
become inactive.) This state is called “wait mode.” (See Table 16.1.1.)
In the wait mode, the power consumption can be saved with Vcc (the power source voltage) retained. When
using no internal peripheral device in the wait mode, the power consumption can be saved furthermore since
each of fsys and internal peripheral device’s operation clock can be inactive. (Refer to section “17.3 Stop
of system clock in wait mode.”) Also, in the wait mode, the state of each I/O pin of the external buses
and bus control signals can be set arbitrarily. Therefore, the power consumption of the whole system can
be saved. (Refer to section “17.2 Bus fixation in stop and wait modes.”)
The wait mode is terminated owing to an interrupt request occurrence or hardware reset.
The wait mode terminate operation is described below.
16.4.1 Terminate operation at interrupt request occurrence
When an interrupt request occurs, each supply of
φCPU and φBIU starts.
The interrupt request which occurred in is accepted.
Table 16.4.1 lists the interrupts which can be used for the wait mode termination.
Table 16.4.1 Interrupts which can be used for wait mode termination
INT3 interrupt: when the key input interrupt is invalid.
When the key input interrupt is selected.
In event counter mode
When an external clock is selected.
Do not use.
NMI interrupt
INTi interrupt (i = 0 to 4)
Key input interrupt
Timer Ai interrupt (i = 0 to 4)
Timer Bi interrupt (i = 0 to 2)
UARTi transmit interrupt (i = 0, 1)
UARTi receive interrupt (i = 0, 1)
A-D conversion interrupt
Notes 1: When multiple interrupts are enabled, the wait mode is terminated owing to the interrupt request which
occurs first.
2: For interrupts, refer to “CHAPTER 7. INTERRUPTS” and each peripheral device’s chapter.
Interrupt
System clock in active
Usage conditions for interrupt request occurrences
System clock stopped
Before executing the WIT instruction, be sure to enable an interrupt which is to be used for the wait mode
termination.
Also, make sure that the interrupt priority level of an interrupt to be used for termination is higher than the
Also, when multiple interrupts in Table 16.4.1 are enabled, the wait mode is terminated owing to the
interrupt request which occurs first.
16.4.2 Terminate operation at hardware reset
Although each of the CPU and SFR area is initialized, the contents of the internal RAM immediately before
the WIT instruction execution are retained. The terminate sequence is the same as the internal processing
sequence after reset.
For reset, refer to “CHAPTER 4. RESET.”
Also, the WIT-instruction-execution status bit is used for the following verification:
Which of the power-on reset and hardware reset has been used to reset the system?
Has the hardware reset been used for the wait mode termination?