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PICList Thread
'Oscillator problem'
1999\03\01@195530 by Biswanath Dutta

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Hi All,

Yeterday I got my first program (you guessed it - a led flasher) working

with  a PIC 16C84.

I'm getting apeculiar problem which I am sure some of you will be able
to solve
for me

1) The circuit works only if I touch pin 16 of the PIC 16C84 and stops
as soon as I remove my finger. It seems that the oscillator does not
work trill I touch it at pin 16 or any track connected to it ,which is
one side of the crystal also.
I did some measurements with a DVM and it reads approx 2.2 volts at pin
16 (roughly average value for a 5 volt square wave) when the circuit is
working and millivolts when it stops working - this means that that
there no oscillations at pin 16. By the way, the oscillations start even

if  I touch the pin  or any track connected to it with the point of a
pencil while holding the wooden
part !
Is this due to wrong configuration or something else ?

2)
In my program I am using  __CONFIG -XT-OSC.
>From Datasheet I get that the configuration word address is 2007. I
open
the .lst file generated by MPASM and I see that it is  2007 here too.
However the Hex file in Intel Hex format shows
:02400E00FD3F74
Here the 3FFD is for the XT oscillator type, but the address is 400E
here  instead of 2007 -- why ?

Awaiting your reply  --  Regards   -- Biswanath Dutta

1999\03\01@203510 by Alice Campbell

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congratulations   Biswanath

let me be the first to congratulate you on your 'blinkie'
<spam_OUTsavlinkTakeThisOuTspamCAL.VSNL.NET.IN>

i have seen this problem on my solderless breadboard.  it means the
board capacitance is messing with your crystal's caps.  this happens
more on the low power xls like 33khz.  i had to solder up a board
before i could get 33 khz to work without tickling it.

alice


some snippage....
{Quote hidden}

1999\03\01@210017 by Gerhard Fiedler

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At 06:06 03/02/99 +0530, Biswanath Dutta wrote:
>In my program I am using  __CONFIG -XT-OSC.
>From Datasheet I get that the configuration word address is 2007. I
>open
>the .lst file generated by MPASM and I see that it is  2007 here too.
>However the Hex file in Intel Hex format shows
>:02400E00FD3F74
>Here the 3FFD is for the XT oscillator type, but the address is 400E
>here  instead of 2007 -- why ?

the addresses in intel hex files are byte addresses, the addresses for pics
are word addresses (for 14-bit  opcodes), which are mapped into the byte
addresses by using 2 bytes for a word. hence pic 0x2007 = intel hex
(0x2007*2)=0x400e. check the file content, you'll see that each two bytes
form one opcode, ie. one (pic) address.

ge

1999\03\01@210641 by Tony Nixon

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Biswanath Dutta wrote:

> Yeterday I got my first program (you guessed it - a led flasher) working

Well done :-)

> Is this due to wrong configuration or something else ?

Do you have capacitors connected to the crystal?

> Here the 3FFD is for the XT oscillator type, but the address is 400E
> here  instead of 2007 -- why ?

The Hex file addresses are twice that of the actual PIC ROM address.
That's because there is a max of 16 data bytes (8 bit) per line, but
that only equals 8 ROM words (16 bit).

--
Best regards

Tony

Multimedia 16F84 Beginners PIC Tools.
** NEW PicNPro Programmer and Port Interface **

http://www.picnpoke.com
Email .....picnpokeKILLspamspam@spam@cdi.com.au

1999\03\02@012516 by Graeme Smith

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GRAEME SMITH                         email: grysmithspamKILLspamfreenet.edmonton.ab.ca
YMCA Edmonton

Address has changed with little warning!
(I moved across the hall! :) )

Email will remain constant... at least for now.


On Tue, 2 Mar 1999, Biswanath Dutta wrote:

{Quote hidden}

I don't know about the rest of you, but this sounds like it might be a
capacitance thing?

Perhaps you need to check your caps, on your xtal?

                               GREY

1999\03\02@114420 by Biswanath Dutta

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Hi All,

Thanks to every one who responded to my query. At least one of my questions is
answered.
As for the oscillator problem, I shall  to work on the hints -- change the
capacitors etc. Shall get back to you.

By the way, its a holiday today here in India -- HOLI -- The festival of
colours.
Everyone goes
around with colours painting each other up in brigt shades of green, red, blue,

purple, even black, and enjoy it enormously.

Happy Holi !!

B.Dutta


'Oscillator problem'
1999\07\01@022412 by William K. Borsum
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At 09:53 PM 6/30/99 -0700, you wrote:
>Does anyone have a method for finding the specified load capacitance for a
>given crystal? aside from just using variable capacitors?

Lots of app-notes out on this.  From my experience its trial and error. But
use smaller values in preference to larger.  15-30 pf is typical.  See the
PIC data book oscillator sections for suggested values.

For example, I recently asked for help trying to get a 37Khz crystal to
start oscillating.  As it finally turned out, my boards were too clean
electronically, and there was not enough noise in the system to kick them
off.  Adding a 100K series resistor solved the problem--provided the
resistor was a NOISY carbon Composition type.  Try finding those in surface
mount!

Kelly

****************************************************************************
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All legitimate attachments to this email will be clearly identified in the
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William K. Borsum, P.E.
OEM Dataloggers and Instrumentation Systems
<.....borsumKILLspamspam.....dascor.com> & <http://www.dascor.com>

1999\07\01@075828 by Robert K. Johnson

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       Did you try that modification over the temperature range the equiptment
was designed to work... Yoou might have some REAL ugly surprises in store
for you... Drift due to lack of sufficient drive and inabllity to startup
at temp extremes are quite likely.

       Robert K. Johnson
       EraseMErkj1spam_OUTspamTakeThisOuTix.netcom.com

At 11:21 PM 6/30/99 -0700, you wrote:
{Quote hidden}

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