Robert Lewis

Pierce Oscillator - no output on XTAL

Discussion created by Robert Lewis on Jun 15, 2006
Latest reply on Jun 15, 2006 by Robert Lewis
We have a Pierce oscillator on a 9s12dg128 part and we have the XCLKS tied to gnd permanently, but I think we are in the Colpits configuration. There is no signal on the XTAL clock output line. There should be a DC offset (sort of) sine wave type signal when the oscillator is working normally, but we see nothing at all. So either the signal is very weak or the processor is not working correctly in the full swing Pierce mode. We have 22pf cap's on the two legs to gnd, and a 1M resistor across the crystal, which is a standard 22pf ECS through hole 16Mhz H49U crystal. The pll is connected but not enabled in the software. Has anyone any ideas about how to determine why there is no output on the XTAL line? The cct is pretty much exactly as in the design spec and app note 2727.

We have VDD1, and VDD2 bypassed with 220nf caps and not connected incorrectly to VCC.

The track and lock bits are set in the CRGFLG register so the oscillator is not in self clock mode but is locked in and tracking. The serial port is working correctly so we know the part is running at the crystal freq of 16Mhz.

Any advice would be appreciated. Thanks inadvance.

Bob

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