CHAPTER 8 WATCHDOG TIMER
User’s Manual U18172EJ2V0UD
146
8.4.3
Watchdog timer operation in STOP mode (when “low-speed internal oscillator can be stopped by
software” is selected by option byte)
The watchdog timer stops counting during STOP instruction execution regardless of whether the system clock or
low-speed internal oscillation clock is being used.
(1) When the watchdog timer operation clock is the system clock (f
X
) when the STOP instruction is executed
When STOP instruction is executed, operation of the watchdog timer is stopped. After STOP mode is released,
operation stops for 34
µ
s (TYP.) (after waiting for the oscillation stabilization time set by the oscillation
stabilization time select register (OSTS) after operation stops in the case of crystal/ceramic oscillation) and then
counting is started again using the operation clock before the operation was stopped. At this time, the counter is
not cleared to 0 but holds its value.
Figure 8-6. Operation in STOP Mode (WDT Operation Clock: Clock to Peripheral Hardware)
<1> CPU clock: Crystal/ceramic oscillation clock
Operation stopped
Operating
Oscillation stabilization time
Normal operation
STOP
Oscillation stabilization time
(set by OSTS register)
Oscillation stopped
Watchdog timer
Operating
f
CPU
CPU operation
Normal
operation
Operation
stopped
Note
<2> CPU clock: High-speed internal oscillation clock or external clock input
Operation stopped
Operating
Normal operation
Oscillation stopped
Watchdog timer
f
CPU
CPU operation
STOP
Operating
Normal
operation
Operation
stopped
Note
Note
The operation stop time is 17
µ
s (MIN.), 34
µ
s (TYP.), and 67
µ
s (MAX.).