AT89S51 watchdog program example

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AT89S51 watchdog program example [Copy link]

AJMP MAIN

MAIN:

;Start watchdog
Mov 0A6H,#01EH ;Send 1E first
Mov 0A6H,#0E1H ;Send E1 later

; Main program
START:

ACALL WDT ;Call reset watchdog subroutine

AJMP START

;Main program

;Reset watchdog subroutine
WDT:
Mov 0A6H,#01EH ;Send 1E first
Mov 0A6H,#0E1H ;Send E1 later
RET

END

Notes:
1. The watchdog of 89S51 must be activated by the program before it starts working. Therefore, it is necessary to ensure that the CPU has a reliable power-on reset.
Otherwise, the watchdog will not work.
2. The watchdog uses the crystal oscillator of the CPU. When the crystal oscillator stops oscillating, the watchdog is also invalid.
3. 89S51 has only a 14-bit counter. The watchdog must be fed at least once in 16383 machine cycles. And this time is
fixed and cannot be changed. When the crystal oscillator is 12M, the watchdog needs to be fed once every 16 milliseconds.

辛昕

Finally, I don't understand why it is 14 bits, is it a dedicated counter for the watchdog?