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'WDT time out periods for sleep - any one intereste'
1998\08\03@093010 by John Kirk

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Hi!

I am working with the 16C58A and found that using the WDT for waking up
from sleep doesn't seem to agree with MircoChip's documentation.   I
found that the sleep period lasted the number of milliseconds given by
the following equation:

msec = 21.9*RATIO + 24

Where RATIO is given in the documentation on the prescaler ( 1:1
RATIO=1, 1:2 RATIO=2, .....1:16 RATIO=16).

Is this information common knowledge?  Is any one interested in this?


John Kirk

1998\08\03@133949 by Andrew Warren

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John Kirk <spam_OUTPICLISTTakeThisOuTspamMITVMA.MIT.EDU> wrote:

> I am working with the 16C58A and found that using the WDT for waking up
> from sleep doesn't seem to agree with MircoChip's documentation.   I found
> that the sleep period lasted the number of milliseconds given by the
> following equation:
>
> msec = 21.9*RATIO + 24
>
> Where RATIO is given in the documentation on the prescaler ( 1:1
> RATIO=1, 1:2 RATIO=2, .....1:16 RATIO=16).

John:

Actually, this DOES agree with Microchip's documentation.

The Watchdog Timer Time-Out Period is TYPICALLY 18 ms, but it
can vary +/- 50% or so (the spec says 9-40 ms).  Your measured
21.9-ms period is pretty close to typical.

There's also a Device Reset Timer Period... It's a short
internal delay on reset to allow your oscillator to stabilize.
On the 16C58A, that DRT period is speced at 9-30 ms (18 ms
typical); again, your measured 24-ms period is within spec.

-Andy

P.S.  The DRT is inactive when the PIC is running on an RC
     oscillator, so if you need faster wake-up times and can deal
     with the oscillator imprecision, you might consider switching
     from a crystal/resonator to an RC.


=== Andrew Warren - .....fastfwdKILLspamspam@spam@ix.netcom.com
=== Fast Forward Engineering - Vista, California
=== http://www.geocities.com/SiliconValley/2499

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