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'How do I verify xtal startup from sleep'
1997\03\21@120617 by Mark Jurras

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I am about ready to switch from emulator to pic16c63 and I am looking for
hints to help me verify that my crystal starts up correctly. When I hang a
scope probe on the CLKOUT pin it sometimes won't start up (emulator with
external xtal). It seems to run fine with no scope probe attached.

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

- -Mark

P.S. Thanks for the Min Max Routines. I combined two of the three to get
what I needed done.

1997\03\21@134147 by Andy Kunz

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>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

==================================================================
Andy Kunz - Montana Design - 409 S 6th St - Phillipsburg, NJ 08865
         Hardware & Software for Industry & R/C Hobbies
       "Go fast, turn right, and keep the wet side down!"
==================================================================

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