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'[PIC]: 1 Minute WDT'
2001\01\06@114718 by Simon-Thijs=20de=20Feber?=

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Hello  All,


Is it possible to have 1 minute WDT on a 16F84 ??
Or should i use an external (interrupt driven) clock
circuit (like PCF8583).


grtz,

Simon

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2001\01\06@171120 by Jinx

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> Is it possible to have 1 minute WDT on a 16F84 ??
> Or should i use an external (interrupt driven) clock
> circuit (like PCF8583).

WDT is probably THE most drift-astic timer and under normal
conditions won't go over 2.5 seconds. At constant temp put
around 25 IRQs together, but you'll never get a repeatable
1.00000 minute.

You need something crystal-driven (WDT is resistor-timed),
either internal or external to the F84, and preferably temperature
compensated.

The easiest and best solution to get long-term accuracy for
the average constructor is counting mains cycles

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2001\01\07@100132 by mike

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On Sun, 7 Jan 2001 11:13:16 +1300, you wrote:

>> Is it possible to have 1 minute WDT on a 16F84 ??
>> Or should i use an external (interrupt driven) clock
>> circuit (like PCF8583).
>
>WDT is probably THE most drift-astic timer and under normal
>conditions won't go over 2.5 seconds. At constant temp put
>around 25 IRQs together, but you'll never get a repeatable
>1.00000 minute.
>
>You need something crystal-driven (WDT is resistor-timed),
>either internal or external to the F84, and preferably temperature
>compensated.
Not necessarily... you can periodically calibrate the WDT against the
xtal/ceramic oscillator, which would give a substantial increase in
accuracy as long as the temperature and supply voltage is fairly
stable between calibrations.

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2001\01\07@165638 by Jinx

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> Not necessarily... you can periodically calibrate the WDT against
> the xtal/ceramic oscillator, which would give a substantial increase
> in accuracy as long as the temperature and supply voltage is fairly
> stable between calibrations.

That would be the way to use the F84 as a thermometer, but if you've
got the xtal to use as a timing reference to measure WDT then.........

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2001\01\08@082805 by mike

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On Mon, 8 Jan 2001 10:55:27 +1300, you wrote:

>> Not necessarily... you can periodically calibrate the WDT against
>> the xtal/ceramic oscillator, which would give a substantial increase
>> in accuracy as long as the temperature and supply voltage is fairly
>> stable between calibrations.
>
>That would be the way to use the F84 as a thermometer, but if you've
>got the xtal to use as a timing reference to measure WDT then.........
If you only want to do things once a minute, you can  save an awful
lot of power by staying in sleep mode, if that's important to you.....

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2001\01\08@083437 by Jinx

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>>That would be the way to use the F84 as a thermometer, but if you've
>>got the xtal to use as a timing reference to measure WDT then.........

>If you only want to do things once a minute, you can  save an awful
>lot of power by staying in sleep mode, if that's important to you.....

Fair enough, horses for courses......

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