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'[PIC]:Watchdog timer reset in 16f84'
2002\02\27@005228 by William Shultz

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Hello all

I am not clear on how to reset the watchdog timer in a 16f84.
I have a controller that I would like to have a reset function, in the event it would lock up or not function properly. I understand how to enable the watchdog but how do I reset to keep it from constantly resetting the micro.

Thanks in advance

Bill Shultz N8HKI

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2002\02\27@010040 by Tony Nixon

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William Shultz wrote:
>
> Hello all
>
> I am not clear on how to reset the watchdog timer in a 16f84.
> I have a controller that I would like to have a reset function, in the event it would lock up or not function properly. I understand how to enable the watchdog but how do I reset to keep it from constantly resetting the micro.
>
> Thanks in advance
>
> Bill Shultz N8HKI

You have to put CLRWDT instructions in strategic places in your code.

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Tony

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2002\02\27@024731 by Jinx

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> You have to put CLRWDT instructions in strategic
> places in your code

By "strategic", Tony means that the CLRWDT instruction
must be executed within the time period of the WDT. If,
for example, you have no pre-scaler on the WDT it will
reset the PIC every 18ms. To avoid that, you must make
sure by some means in your software that the CLRWDT
is executed before each and every expected WDT reset.

How you do that depends on the structure of your program.
Although I haven't done this myself, you could use the TMR0
interrupt to call a routine with CLRWDT in it if you do not
have convenient looping withing the program otherwise. As
you also wish to have a reset in case of a fault, you should
be able to arrange things so that the CLRWDT is not executed
in that case.

Using the pre-scaler with WDT will increase the reset period
to a little over 2 seconds, which may or may not be useful to you.
Note though that the pre-scaler has to be assigned to either
WDT or TMR0 and that the division ratio of the pre-scaler is
not the same with WDT as it is with TMR0

And you'll know that the F628 is preferable to the F84 if you're
getting new stock

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2002\02\27@081950 by Olin Lathrop

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> I understand how to enable the watchdog but how do I reset
> to keep it from constantly resetting the micro.

CLRWDT


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, .....olinKILLspamspam@spam@embedinc.com, http://www.embedinc.com

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2002\02\27@105038 by Herbert Graf

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Excecute the instruction CLRWDT in code that you know is OK. TTYL

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2002\02\28@060837 by William Shultz

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Yes, a friend of mine has introduced me to the f628. Looks to be cheaper and
much more versitile than the f84. I am going to move to this for the small
number of units I have to make.

thanks


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