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PICList Thread
'Slow startup'
1998\04\28@225007 by Anthony Tekatch

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I've been having some difficulties with my PIC project taking about 5
seconds to start up from a power up or a reset or wake from sleep.

I have a 16C63-JW running on a 32KHz crystal (Epson C-001R32.768K-A) with
68pF capacitors and a series OSC2 resistor of 100Kohm. I am relying on the
power on RESET timer to do the reset.

I think that the slow wake up/reset is due to the 32KHz crystal driving
but I ended up burning out crystals when I used lower series resistance
like 1K or 0 ohms.

It seems that if I put the unit to sleep then wake it up within one or two
seconds that it will wake up much quicker (2 seconds wake up time instead
of 5 seconds).


Any help would be appreciated.


spam_OUTanthony.tekatchTakeThisOuTspamsympatico.ca

1998\04\29@004159 by tjaart

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Anthony Tekatch wrote:

> I've been having some difficulties with my PIC project taking about 5
> seconds to start up from a power up or a reset or wake from sleep.
>
> I have a 16C63-JW running on a 32KHz crystal (Epson C-001R32.768K-A) with
> 68pF capacitors and a series OSC2 resistor of 100Kohm. I am relying on the
> power on RESET timer to do the reset.
>
> I think that the slow wake up/reset is due to the 32KHz crystal driving
> but I ended up burning out crystals when I used lower series resistance
> like 1K or 0 ohms.
>
> It seems that if I put the unit to sleep then wake it up within one or two
> seconds that it will wake up much quicker (2 seconds wake up time instead
> of 5 seconds).
>
> Any help would be appreciated.

It sounds like you are using the the XT or HS oscillator
selection instead of LP (low power)

--
Friendly Regards

Tjaart van der Walt
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1998\04\29@004210 by Steve Baldwin

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> I have a 16C63-JW running on a 32KHz crystal (Epson C-001R32.768K-A) with
> 68pF capacitors and a series OSC2 resistor of 100Kohm. I am relying on the
> power on RESET timer to do the reset.
>
> I think that the slow wake up/reset is due to the 32KHz crystal driving
> but I ended up burning out crystals when I used lower series resistance
> like 1K or 0 ohms.

The resistance sounds right but the capacitance is an order of
magnitude out. Watch crystals are usually around the 10-12pF load
capacitance. The extra will be attenuating it enough that you would
expect it to start slowly, although with that amount, you should be
happy that it starts at all.
Drop your capacitors to around 20pF.

Steve.



======================================================
Steve Baldwin                Electronic Product Design
TLA Microsystems Ltd         Microcontroller Specialists
PO Box 15-680, New Lynn      http://www.tla.co.nz
Auckland, New Zealand        ph  +64 9 820-2221
email: .....stevebKILLspamspam.....tla.co.nz      fax +64 9 820-1929
======================================================

1998\04\29@183219 by Anthony Tekatch

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>The resistance sounds right but the capacitance is an order of magnitude
>out. Watch crystals are usually around the 10-12pF load capacitance. The
>extra will be attenuating it enough that you would expect it to start
>slowly, although with that amount, you should be happy that it starts at
>all.
>Drop your capacitors to around 20pF.


That's exactly what the problem was. The MICROCHIP spec sheet for the
16C63 (Pic16f8x pg39) says that they tested the oscillator on 68pF-100pF
(LP mode for 32kHz) in their capacitor selection (table 8-2). I guess that
must be a mistake??

I had a 10pF and a 12pF laying around to test this on and my project
starts up very quickly now.

Thank you very much Steve.


EraseMEanthony.tekatchspam_OUTspamTakeThisOuTsympatico.ca

1998\04\29@185031 by David VanHorn

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>
>That's exactly what the problem was. The MICROCHIP spec sheet for the
>16C63 (Pic16f8x pg39) says that they tested the oscillator on 68pF-100pF
>(LP mode for 32kHz) in their capacitor selection (table 8-2). I guess that
>must be a mistake??
>
>I had a 10pF and a 12pF laying around to test this on and my project
>starts up very quickly now.

If you have the ratings on that xtal, check what load caps it was cut for,
and do that.
Otherwise it will not run at the right speed.  Hard starting is symptomatic
of being WAY off.

1998\04\30@021817 by Claudio Rachiele IW0DZG

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                  Status Distribution April 29, 1998 04:44:02

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