How to implement watch dog timer in AT89S51?

watch dog Timer

Hi
I am using AT89S51 can any one tell how to implement watch dog timer with some code example.

watch dog Timer

I think WDT should be implemented in HW, example: X25045

Re: watch dog Timer

Hi
I am using AT89S51 can any one tell how to implement watch dog timer with some code example.

Click to expand...

What language, what compiler?

Mr.Cube

Re: watch dog Timer

Hi
I am using assambly and Keil software

watch dog Timer

Salam,

WDT is consist of

[1] 14-Bit Counter (Count from 0 ---> 3FFF )
[2] WDTRST SFR (Write only)

The WDT is disabled by defult
To Start the WDT Use two instructions

WDTRST=0x1e;
WDTRST=0xe1;

The WDT start to count from 0 to 3FFF (16383)
When The WDT overflow it will drive RST pin High for time equal to 98*Tosc (Where Tosc=1\Fosc)

The WDT will increment every one machine cycle while the oscillator is running.

Example
----------
If you are connecting your 8051 to 12 MHZ crystal.

Then WDT will increment every 1uS
WDT overflow after 16384uS increments and reset your microcontroller.

To avoid WDT reset your micro, you must put the following instructions in the begining of your periodically calling functions.

WDTRST=0x1e;
WDTRST=0xe1;

Have Fun
Bye

Re: watch dog Timer

Read this articles:
"Introduction to Watchdog Timers" by Michael Barr
**broken link removed**
"Watchdog Timers" by Niall Murphy
**broken link removed**