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WATCHDOG TIMER
9.2 Operation description
(1) Example of program runaway detection
Write to the address 60
becomes "0." In the case that Watchdog timer is used to detect a program runaway, if writing to
address 60
is not performed owing to a program runaway, the watchdog timer interrupt request
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occurs when the most significant bit of Watchdog timer becomes "0." It means that a program
runaway has occurred.
To reset the microcomputer after a program runaway, write "1" to the software reset bit (bit 3 at
address 5E
) in the watchdog timer interrupt routine.
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Watchdog timer register
(Address 60
Watchdog timer
interrupt request occur
(program runaway detected)
Notes 1: Initialize (write to address 60
Watchdog timer becomes "0" (the watchdog timer interrupt request occurs).
2: When the program runaway occurs, values of the data bank register (DT) and direct
page register (DPR) may be changed. When "1" is written to the software reset bit by
the addressing mode using DT and DPR, set values to DT and DPR again.
Fig. 9.2.1 Example of program runaway detection by Watchdog timer
9–6
(watchdog timer register) before the most significant bit of Watchdog timer
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Main routine
)
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Watchdog timer interrupt routine
Software reset bit
(Address 5E
, b3)
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RTI
) Watchdog timer before the most significant bit of
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7751 Group User's Manual
8-bit dummy data
"1" (Note 2)
Reset microcomputer
Watchdog timer initialized
Value of watchdog timer :
"FFF
" (Note 1)
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