STOP AND WAIT MODES
7902 Group User’s Manual
16-2
16.1 Overview
When there is no need for operation of the central processing unit (CPU), the stop and wait modes are used
to stop oscillation or internal clock. As a result, the power consumption can be saved. The microcomputer
enters the stop mode when the STP instruction has been executed; the microcomputer enters the wait mode
when the WIT instruction has been executed.
The stop and wait modes are terminated by an interrupt request occurrence or hardware reset.
Table 16.1.1 lists the states in the stop and wait modes and operations after these modes are terminated.
Table 16.1.1 States in stop and wait modes and operations after these modes are terminated
Active.
Operates (Note 1).
Inactive.
Active.
Inactive.
Operates.
Stopped.
Retains the state at the WIT instruction execution (Note 2).
Floating (Note 2).
Outputs “H” level (Note 2).
Outputs “L” level (Note 2).
Outputs clock
φ1 (Note 2).
Retains the state at the WIT instruction execution.
Inactive.
Can operate only in the
event counter mode.
Can operate only when an
external clock is selected.
Stopped.
Outputs “L” level (Note 2).
Internal
peripheral
devices
When watchdog timer is used at
termination (See Figure 16.3.1.)
Stop mode
Operation after hardware reset
A0 to A23
D0 to D15
RD, BLW,
BHW, HLDA,
CS0 to CS3
ALE
φ1
The others
Inactive.
Stopped.
Inactive.
Can operate only in the event counter mode.
Can operate only when an external clock is
selected.
Stopped.
Retains the state at the STP instruction execution (Note 2).
Floating (Note 2).
Outputs “H” level (Note 2).
Outputs “L” level (Note 2).
Retains the state at the STP instruction execution.
Pins
Timers A, B
Serial I/O
A-D converter
D-A converter
Watchdog timer
States
Supply of
φCPU, φBIU starts after a
certain time has been measured
by using the watchdog timer.
Oscillation
PLL frequency multiplier
φCPU, φBIU
fsys, clock
φ1,
f1 to f4096
Wf32, Wf512
Operation
after
termination
When watchdog timer is not used
at termination (See Figure 16.3.1.)
Wait mode
System clock is active.
(Bit 3 at address 6316 = “0”)
System clock is inactive.
(Bit 3 at address 6316 = “1”)
Supply of
φCPU, φBIU starts
immediately after termi-
nation (Note 3).
Operation after hardware reset
Supply of
φCPU, φBIU starts immediately after
termination.
Notes 1: This applies when the PLL circuit operation enable bit (bit 1 at address BC16) = “1.”
2: The I/O pins of the external buses and bus control signals can be switched to programmable I/O port
pins by software. (Refer to section “17.2 Bus fixation in stop and wait modes.”)
3: See Table 16.3.2.
Item
Termination due
to interrupt request
occurrence
Termination due
to hardware reset