CHAPTER 9 WATCHDOG TIMER
Preliminary User’s Manual U16846EJ1V0UD
179
9.4.3 Watchdog timer operation in STOP mode (when “Ring-OSC can be stopped by software” is selected by
option byte)
The watchdog timer stops counting during STOP instruction execution regardless of whether the high-speed
system clock or Ring-OSC clock is being used.
(1) When the CPU clock and the watchdog timer operation clock are the high-speed system clock (f
XP
) when
the STOP instruction is executed
When STOP instruction is executed, operation of the watchdog timer is stopped. After STOP mode is released,
counting stops for the oscillation stabilization time set by the oscillation stabilization time select register (OSTS)
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 9-4. Operation in STOP Mode (CPU Clock and WDT Operation Clock: High-Speed System Clock)
Watchdog timer
Operating
Operation stopped
Operating
f
R
f
XP
CPU operation
Normal
operation
STOP
Oscillation stabilization time
Normal operation
Oscillation
stopped
Oscillation stabilization time
(set by OSTS register)
(2) When the CPU clock is the high-speed system clock (f
XP
) and the watchdog timer operation clock is the
Ring-OSC clock (f
R
) when the STOP instruction is executed
When the STOP instruction is executed, operation of the watchdog timer is stopped. After STOP mode is
released, 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 9-5. Operation in STOP Mode
(CPU Clock: High-Speed System Clock, WDT Operation Clock: Ring-OSC Clock)
Watchdog timer
Operating
f
R
f
XP
CPU operation
Normal
operation
STOP
Oscillation stabilization time
Normal operation
Oscillation
stopped
Oscillation stabilization time
(set by OSTS register)
Operating Operation stopped