>external xtal). It seems to run fine with no scope probe attached.

Hopefully the production model comes without a scope attached <G>.

>How does one look at the xtal? I am using an ECS crystal from Digi-Key
>#X-405-ND.

The problem is due to the capacitance loading of the probe.  Try a
different probe for starters.

If you really need to very oscillation, do it this way:


-------|
        |
P osc1  |------o--||---- GND
I       |       |
C       |       XTAL
        |       |
  osc2  |------o--||---- GND
        |       |
-------|        |
                +----|>o----TEST POINT


This way, the xtal has a fixed extra load on the output (the logic inverter
input), and you can check at the output of the gate with your probe to
verify oscillation without adding a varying load.

It matters which osc pin you use, too.

FWIW, use this with a variable cap to be able to set yourself a
deadly-accurate xtal frequency.  You will see a square wave rather than a
sine wave.

Andy

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Andy Kunz - Montana Design - 409 S 6th St - Phillipsburg, NJ 08865
          Hardware & Software for Industry & R/C Hobbies
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