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PICList Thread
'16F877 xt oscilator problem'
1999\11\12@032011 by Leo

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Hi PICer friends,

I'm using the 16F877 for the first time and I have trouble to start the xt
oscillator.

the connection on the 16F877 are:

vcc - to pin 11 - 32 wired togheter
gnd - to pin 12 - 31 wired togheter
mclr - to wcc thorught a resistor of 10K
xt osc - to pin 13 and 22 pf capacitor to gnd
xt osc - to pin 14 and 22 pf capacitor to gnd
rb3 - floating  (but have been tested connected to the vcc and gnd)

the xt are a 4 Mhz quartz

Using the blink8x.bas sample program in PBP 2.2 I compile it and I'm able to
load the hex into the pic and I can read back the code (that means the PIC
is working) but the oscillator do not start.

On pin 14 I can see with a scope a stable level of 2,6 volt and on pin 13 a
stable level of 2,0 volt .

Dear PICer friends, do you have any idea to help me to solve this problem?


Ciao

Leo


For reference purpose you can see the PBP blink8x.bas source:

i       var     byte    ' Define loop variable
LEDS    var     PORTD   ' Alias PORTD to LEDS
TRISD = %00000000       ' Set PORTD to all output
loop:   LEDS = 1        ' First LED on
Pause 500       ' Delay for .5 seconds
For i = 1 to 7  ' Go through For..Next loop 7 times
LEDS = LEDS << 1        ' Shift on LED one to left
Pause 500       ' Delay for .5 seconds
Next i
Goto loop       ' Go back to loop and blink LED forever
End

1999\11\12@053555 by Jim Robertson

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At 09:21 12/11/99 +0100, you wrote:

Have you selected the XT oscillator option in the config word?

Jim


{Quote hidden}

Regards,

Jim Robertson
NEWFOUND ELECTRONICS
________________________________________
Email: spam_OUTnewfoundTakeThisOuTspampipeline.com.au
http://www.new-elect.com
MPLAB compatible PIC programmers.
________________________________________

1999\11\12@103650 by Dave Johnson

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Leo wrote:

>Dear PICer friends, do you have any idea to help me to solve this problem?
I had some startup trouble with an '877 and a 4MHz ceramic resonator from
Murata. Increasing the configuration bit to HS helped (higher drive from
the PIC) but I didn't like that. A look at Murata's website suggested a
1M resistor across the resonator, so I tried that and I haven't had any
trouble since. I assume the same trick with crystal would work, it's
worth a try.

Dave Johnson

1999\11\13@104802 by Myke Predko

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face
Hi Leo,

Your problem is that you aren't disabling the "LVP".  Specify "_LVP_OFF" in
your "__CONFIG" Statement and everything will run fine.

I had the same problem a few weeks ago.

myke
{Original Message removed}

1999\11\17@110126 by Leo

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Hi Mike,

thanks for your suggestion.


Ciao


Leo
----- Original Message -----
From: Myke Predko <.....mykeKILLspamspam@spam@PASSPORT.CA>
To: <PICLISTspamKILLspammitvma.mit.edu>
Sent: sabato 13 novembre 1999 16.47
Subject: Re: 16F877 xt oscilator problem


> Hi Leo,
>
> Your problem is that you aren't disabling the "LVP".  Specify "_LVP_OFF"
in
{Quote hidden}

xt
{Quote hidden}

able
> to
> > load the hex into the pic and I can read back the code (that means the
PIC
> > is working) but the oscillator do not start.
> >
> > On pin 14 I can see with a scope a stable level of 2,6 volt and on pin
13
> a
> > stable level of 2,0 volt .
> >
> > Dear PICer friends, do you have any idea to help me to solve this
problem?
{Quote hidden}

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