At 17:00 7/11/99 -0500, you wrote:
>Hi Dennis,
>
>At 08:50 AM 11/8/99 +1100, you wrote:
>>
>>No, the WDT comes off the XTAL
>>
>>
>
>Which chip are you talking about? I believe they are all the same with
>respect to the WDT,and the following is quoted from the 16F84 datasheet,
>page 50:
>
>"The Watchdog Timer is a free running on-chip RC
>oscillator which does not require any external
>components. This RC oscillator is separate from the
>RC oscillator of the OSC1/CLKIN pin. That means that
>the WDT will run even if the clock on the OSC1/CLKIN
>and OSC2/CLKOUT pins of the device has been
>stopped, for example, by execution of a SLEEP
>instruction."
>

Yep sorry about that, was thinking of 8605 stuff when I wrote this. I
should have twigged when I was thinking about how sloppy it is.



>>WDT would not detect brownout unless that brownout condtions:-
>>1/ Kept the XTAL runing
>>2/ Caused the programme to stop running such that the WDT timer would go
off.
>
>Well, it would not have to do #1 or #2. However, I suppose that it is
>possible that a brown-out could cause the WDT's RC oscillator to stop OR
>prevent the prescaler/counter from registering its pulses and causing a
>reset. SO, it isn't a reliable brown-out detector.
>
>>
>>Remember that in brownout it is unknown what is read and written to ports
>>and RAM, there is a chance that the WDT would and could be written correctly
>>
>>
>
>Yes
>
>>>How many times should we have CLRWDT in our code? Your right -
>>> only once. Even though I sometimes do it myself, any more than
>>>once is asking for trouble.
>>
>>Yes
>
>Well, I can see how it is BEST to only place it in your code once (reduce
>the chance that the code would lock up by running an infinite loop it isn't
>supposed to) ,but not always possible. I could have two loops in my code
>that wait for some kind of event or input,and are so tight that they cannot
>branch to a separate part of the code to run a CLRWDT.
>

Bad code Sean, re-organise it to remove this potential problem.

Dennis

>
>Sean
>
>