Post by thread:How does Watchdog Timer works ?

Hi, it works exactly as the aware-testing device in the locomotive. The leader must push a knob within a given time or the train stops. Watchdog timer has its own timeout if configured; it is either 18 msec or 18 msec * prescaler. You must clear the watchdog timer via ClrWdt instruction within the given time period or a reset process starts. Of course, clearing the WDT restarts its time period. I use it extensively, because of my program does not do what I have intended, it branches another path and maybe there is no ClrWdt and it resets. So I see immediately what is going on. Watchdog generally has the job to put a system in a definite state in a case of hard/software malfunction (rather software). For instance: bsf LED loop: nop goto loop will cause a reset. bsf LED loop: ClrWdt goto loop won't. I hope this helps. Imre On Tue, 17 Nov 1998, fctan wrote: > What is the theory behind a watchdog timer and prescaler. How does the > program know when the timer is time-out ? > >

> Van: fctan <spam_OUTfctanTakeThisOuTKSMK.ITM.EDU.MY> > Aan: .....PICLISTKILLspam@spam@MITVMA.MIT.EDU > Onderwerp: How does Watchdog Timer works ? > Datum: dinsdag 17 november 1998 6:43 > > What is the theory behind a watchdog timer and prescaler. How does the > program know when the timer is time-out ? Think of the WachDog-timer as a bucket. Think of the Pre-Scaler as a valve. You are pouring water into the bucket thru the valve. If the valve is open just a little (the pre-scaler divides by 256) the bucket will be filled slowly. If the valve is opened a lot (the pre-scaler divides by 16) the bucket will fill quite fast. If the bucket is full (The Watch-dog-timer overflows) you have to Re-start whatever you where doing (the controller is Reset). So, every once-in-a-while you go to the bucket and empty it (Reset the Watch-dog : CLRWDT). If you can't do that because you are doing something that will not end (the controller is stuck in a never-ending loop) the bucket wil overflow and you will be forced to re-start : The non-ending occupation ended. By the way : You can choose to generate an Interrupt when the WatchDog overflows. Greetz, Rudy Wieser