Roelof Klunder

Clock modes

Discussion created by Roelof Klunder on Jan 22, 2007
Latest reply on Jan 22, 2007 by Roelof Klunder
We are using the MC9S12DT256. Normally it is has a colpit clock circuit, which is working without any problems at 16MHz.
 
Now we need to have a large clock signal amplitde to synchronize it with other ICs on the same board. So I want to run it in Pierce-clock mode. So I changed PE7/XCLKS_not to ground and placed two capacitance from XTAL and EXTAL to ground (15pF) and parallel to the Crystal a resistor of 3MOhm.  And I removed the series capacitance.
 
But now the processor is runing on a low clock frequency (internal clock), and I measure no clock signal on EXTAL and XTAL pins. I also see no DC voltage on these pins (VDDPLL is above 2V).
 
So my question is:
- Is our processor able to run in Pierce mode?
- Do I need to change more than the clock circuit, and pull-up/down resistor connected to PE7? (some code perhaps?)
- Should there be a DC voltage on the EXTAL and XTAL pins?
 
 
 

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