LAPIS Semiconductor ML610421, Руководство пользователя, Страница: 178 / 437

ML610Q421/ML610Q422/ML610421 User’s Manual
Chapter 13 Watchdog Timer
12 – 6
Figure 12-2 shows an example of watchdog timer operation.
Figure 12-2 Example of Watchdog Timer Operation

The WDT counter starts counting after the system reset has been released and the low-speed clock oscillation start.

The overflow period of the WDT counter (TWOV) is set to WDTMOD.

“5AH” is written to WDTCON. (Internal pointer 0
→
1)

“0A5H” is written to WDTCON and the WDT counter is cleared. (Internal pointer 1
→
0)

“5AH” is written o WDTCON. (Internal pointer 0
→
1)

When “5AH” is written to WDTCON after the occurrence of abnormality, it cannot be accepted as the internal
pointer is set to “1”. (Internal pointer 1
→
0)

Although “0A5H” is written to WDTCON, the WDT counter is not cleared since the internal pointer is “0” and the
writing of “5AH” is not accepted in

. (Internal pointer 0
→
1)

The WDT counter overflows and a watchdog timer interrupt request (WDTINT) is generated. In this case,, the WDT
counter and the internal pointer (WDP) are initialiaed for a half cycle of low speed clock (about 15.26us).

If the WDT counter is not cleared even by the software processing performed following a watchdog timer interrupt
and the WDT counter overflows again, WDT reset occurs and the mode is shifted to a system reset mode.
Note:
•
In STOP mode, the watchdog timer operation also stops.
•
In HALT mode, the watchdog timer operation does not stop. When the WDT interrupt occurs, the HALT mode is
released.
•
The watchdog timer cannot detect all the abnormal operations. Even if the CPU loses control, the watchdog timer
cannot detect the abnormality in the operation state in which the WDT counter is cleared.

5A

A5

5A

5A
Occurrence of
abnormality

A5
T
WOV
Overflow period
Overflow
Low-speed
oscillation start
Program
start
5A A5
Data:
RESET_S
System reset
WDTCON Write
WDTP
Internal pointer
WDT counter
WDTINT
WDT interrupt
WDT reset
T
WOV
Overflow period

WDTMOD
setting
WDTMOD
setting

Occurrence of
WDTINT

Occurrence of
WDT reset