The specific usage of the watchdog is as follows:
in the program initialization, first write 01EH and then write 0E1H to the watchdog register (WDTRST address is 0A6H). This activates the watchdog.
code
org 0000
Ljmp begin
Begin:
Mov 0A6H,#01EH ;Send 1E first
Mov 0A6H,#0E1H ;Send E1 later
;Activate the watchdog in program initialization.
……
……
For:
……
Mov 0A6H,#01EH ;Send 1E first
Mov 0A6H,#0E1H ;Send E1 later
;Feed the watchdog instruction
……
Ljmp for
In C language, add a declaration statement.
Add a line sfr WDTRST = 0xA6 in the AT89X51.h declaration file;
code
Main()
{
WDTRST=0x1E;
WDTRST=0xE1; //Initialize the watchdog.
While (1)
{
WDTRST=0x1E;
WDTRST=0xE1; //Feed the watchdog
}
}
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.
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