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'Osc Help!'
1997\09\29@090017 by Shabbir A Bashar

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-- [ From: Shabbir A Bashar * EMC.Ver #2.5.02 ] --

Hi all,

I am more into electronics than programming but I'm just starting on
the PIC 16c84.

I wired up my first circuit yesterday (just the 5V regulator, pic and
a crystal oscillator).

The oscillator is the standard recommended setup -  4Mhz crystal and
2 27 pF capacitors running from each side of the crystal to 0V.

I programmed the PIC (using a separate programmer and software that I
know works) with a simple routine that should  output 00101 on PORTA
and set PORTB running as a decrementing counter. Both ports are set
to output. PWRON reset pin is tied directly to +5V (as in the
sheets).

All I wanted to do was to probe the pins and assure myself that the
thing's actually doing as it is told.

However, I get nothing (other than the correct voltages at drain and
source ports).

Using my nasty (ancient) oscilloscope I can not detect any
oscillations coming from either clock pin. One of the clock pins is
at 0V and the other sits at roughly 0.24V.

The XTal fuse was set when I programmed the pic.

Any ideas??

Antonio

spam_OUTantonioTakeThisOuTspamvilches.idiscover.co.uk

--
Shabbir A. Bashar
Research Associate, Centre for Optics & Electronics
Dept. of Electronics Engineering
King's College London, WC2R 2LS, UK
E-mail : .....s.basharKILLspamspam@spam@kcl.ac.uk
http://www.spods.dcs.kcl.ac.uk/~sb/sab/sab.htm
Tel. : +44 (0)171 836 5454 ext. 3606
Fax  : +44 (0)171 873 2844 or 836 4781

1997\09\29@092151 by Pasi T Mustalahti

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On Mon, 29 Sep 1997, Shabbir A Bashar wrote:

> I programmed the PIC (using a separate programmer and software that I
> know works) with a simple routine that should  output 00101 on PORTA
> and set PORTB running as a decrementing counter. Both ports are set
> to output. PWRON reset pin is tied directly to +5V (as in the
> sheets).
> However, I get nothing (other than the correct voltages at drain and
> source ports).
>
PTM: Remember that portA and TrisA are at different register pages. There
is a bit for shifting pages. (I made this error once)

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PTM, pasi.mustalahtispamKILLspamutu.fi, .....ptmustaKILLspamspam.....utu.fi, http://www.utu.fi/~ptmusta
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1997\09\29@093358 by Norm Cramer

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At 01:56 PM 9/29/97 -0500, you wrote:
>-- [ From: Shabbir A Bashar * EMC.Ver #2.5.02 ] --
>
>I programmed the PIC (using a separate programmer and software that I
>know works)

How do you know that it works?  Did you run it in MPLAB?  The code should
be short so post it.  Most times I have had this kind of problem it was a
software problem.

Besides checking the program itself, you configuration may be wrong.  Did
you leave the WDT enabled and if so, are you clearing it in your code?

Norm

1997\09\29@142122 by Eric van Es

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Hi

You could always try clocking the PIC by hand! Contact bounce will
probably ruin it for anything else, but just to set the pins should be
OK.

Else someone or myself could send you a working prog to test your set-up!

Cheers!
--
Eric van Es               | Cape Town, South Africa
EraseMEvanesspam_OUTspamTakeThisOuTilink.nis.za | http://www.nis.za/~vanes
LOOKING FOR TEMPORARY / HOLIDAY ACCOMODATION?
http://www.nis.za/~vanes/accom.htm

1997\09\29@143052 by Mike Keitz

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On Mon, 29 Sep 1997 13:56:30 -0500 Shabbir A Bashar <s.basharspamspam_OUTKCL.AC.UK>
writes:
>-- [ From: Shabbir A Bashar * EMC.Ver #2.5.02 ] --
>
>Hi all,
>
>I am more into electronics than programming but I'm just starting on
>the PIC 16c84.
>

>However, I get nothing (other than the correct voltages at drain and
>source ports).
>
>Using my nasty (ancient) oscilloscope I can not detect any
>oscillations coming from either clock pin. One of the clock pins is
>at 0V and the other sits at roughly 0.24V.

Measuring with a high-impedance device like a scope or digital voltmeter,
you should have about 2.5V at both oscillator pins, whether the
oscillator is running or not.  About the only thing that can change this
is executing a SLEEP instruction or setting the oscillator fuses to the
RC type.  Looking for oscillations with a scope is not a reliable test
since the loading of the scope may make the oscillator start or stop.
But the DC voltage should set itself to half-supply.

I've seen a PIC16F84 do strange things when the power comes up slowly (as
can happen if the input of your 5V regulator is driven from a small
transformer with a large filter capacitor).  The oscillator refusing to
work was not one of those strange things but it could happen.


>
>The XTal fuse was set when I programmed the pic.

Put the PIC back in the programmer and read it, make sure the fuse is
actually set that way.  Be sure to disable the WDT.  Leaving it on will
cause the PIC to reset itself periodically.  Try to pull one of the pins
that should be output to +5 and ground with a resistor, if the voltage
does follow then the tri-state register hasn't been set.  This could be
because the program isn't running at all, or it could be improper
software.  All the pins change to input mode when the chip is reset.

{Quote hidden}

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