Re: [avr-gcc-list] My first time with AVR (help)

[Richard Urwin]

On Sunday 18 Jan 2004 8:33 am, Karl Bongers wrote:
> On Sun, Jan 18, 2004 at 07:26:05PM +0100, Helix wrote:
> > Herb
> > Thank you for the answer.
> >
> > >  > About the oscillator it is a 7.378Mhz
> > >  > But I don't know how to test it, schould I connect the oscilloscope
> >
> > between
> >
> > >  > the Quartz pins or between GND and one of the Quartz pin ?
> > >
> > > Check the clock pins on the cpu.
> >
> > Okay, I put the scope on pin 14, 15 of my 8515 (XTAL1 XTAL2)
> > And I'm unable to see any clock
> > My XTAL is a 7.378Mhz with two 22n capacitors connected to GND
>
> I see XTAL on 12,13 for a 40-pin 8535, I forget if these are
> the same footprint.  Check your datasheet, make sure you have the
> right pins for crystal, power, gnd.

If you're using wire wrap or some other technique on the underside of the 
board, remember the pins are strangely reversed. Check them carefully.

> The XTAL pins should show oscillation on scope, with reset in any
> state.

Not tried that with an AVR, and I seem to remember I never had much luck doing 
that with other chips, but the datasheets I have (AVR1200) show XTAL 2 is 
capable of driving a HCMOS buffer. It may be best to scope XTAL 2 against 
ground. Remember your scope ground is probably connected to mains earth, and 
if you're using a power supply, that will usually earth its 0V as well. So 
unless you're measuring against ground you may be shorting out something.

-- 
Richard Urwin