Panasonic F77G, MN101C77C Watchdog Timer Period, The Lowest Value for Watchdog Timer Clear

Models: F77G MN101C77C

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Chapter 9 Watchdog Timer

„How to Clear Watchdog Timer

The watchdog timer can be cleared by writing to the watchdog timer control register (WDCTR). The watchdog timer can be cleared regardless of the writing data to the register. The bit-set (BSET) that does not change the value is recommended.

„Watchdog Timer Period

The watchdog timer period is decided by the bp2, 1 (WDTS1-0) of the watchdog timer control register (WDCTR) and the system clock (fs). If the watchdog timer is not cleared till the set period of watchdog timer, that is regarded as an error and the watchdog interrupt (WDIRQ) of the non-maskable interrupt (NMI) is generated.

Table 9-3-1 Watchdog Timer Period

WDTS1

WDTS0

Watchdog time-out period

 

 

 

 

0

0

216

X system clock

0

1

218

X system clock

1

0

220

X system clock

1

1

222

X system clock

System clock is decided by the CPU mode control register (CPUM).

[

Chapter 2 2-5. Clock Switching ]

The watchdog timer period is generally decided from the execution time for main routine of program. That should be set the longer period than the value of the execution time for main routine divided by natural number (1, 2, , , ). And insert the instruction of the watchdog timer clear to the main routine as that value makes the same cycle.

„The Lowest Value for Watchdog Timer Clear

The lowest value for watchdog timer clear is decided by the bp5, 4, 3 (WDTC2, WDTC1, WDTC0) of the watchdog timer control register (WDCTR).

Table 9-3-2 The Lowest Value for Watchdog Timer Clear

WDTC2

WDTC1

WATC0

Watchdog timer can be cleared at the

following cycle or more

 

 

 

 

 

 

 

 

0

0

0

 

no limit

 

 

 

 

 

0

0

1

27

X system clock

 

 

 

 

 

0

1

0

29

X system clock

 

 

 

 

 

0

1

1

211

X system clock

1

0

0

213

X system clock

1

0

1

215

X system clock

1

1

0

217

X system clock

1

1

1

219

X system clock

Operation IX - 5

Page 317
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Panasonic F77G, MN101C77C user manual Watchdog Timer Period, The Lowest Value for Watchdog Timer Clear