How to use 89S51 watchdog

The 89S51 and 89C51 in ATMEL's 89S51 series have the same functions. The instructions are compatible. HEX programs can be used directly without any conversion. The 89S51 only adds a watchdog function compared to the 89C51. For other functions of the 89S51, please refer to the 89C51 data.

The specific usage of the watchdog is as follows:

In the initialization of the program, write 01EH first and then 0E1H to the watchdog register (WDTRST address is 0A6H) to activate the watchdog.

Org 0000

Ljmp begin

Begin:

Mov 0A6H,#01EH ; send 1E first

Mov 0A6H,#0E1H ; send to E1

;Activate the watchdog during program initialization.

…

…

For:

…

Mov 0A6H,#01EH ; send 1E first

Mov 0A6H,#0E1H ; send to E1

;Feed the dog command

…

Ljmp for

In C language, a declaration statement needs to be added.

Add a line sfr WDTRST = 0xA6 in the AT89X51.h declaration file;

Main()

{

WDTRST=0x1E;

WDTRST=0xE1; //Initialize watchdog.

While (1)

{

WDTRST=0x1E;

WDTRST=0xE1; //Dog feeding instruction

}

}

Note:

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 CPU crystal oscillator. When the crystal oscillator stops oscillating, the watchdog is invalid.

3. 89S51 has only 14-bit counter. The dog 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 dog must be fed once every 16 milliseconds.