Ruth Hendrix

Oscillator questions on HCS12C32

Discussion created by Ruth Hendrix Employee on Jan 26, 2006
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Posted: Fri Aug 19, 2005 8:27 am    

I´m designing a board with the HCS12C32 and the question is what oscilator to use. The pierce oscillator seems to be more reliable to me. Can the PLL be used when a pierce config is used and can the PLL be used when configured as pierce and driven by a canned oscillator ?
Posted: Mon Aug 22, 2005 3:23 pm    
The PLL is independent of the oscillator chosen so pick the one you are most familiar with (probably pierce). I'm pretty sure the oscillator guide gives an example of the oscillator being driven by a can, have a look to see if there is any further info.
Posted: Wed Aug 24, 2005 8:56 pm    
Go with Pierce man. The Colpitts option is ideal for low-power applications but is very sensitive to stray capacitance (for example, from board traces). The PLL uses the output from the oscillator block as an input and because the clock type switching is performed there, it doesn't care about oscillator type. Remember to set PE7 (I think, it's been a couple of years since I had my hands on C32!) to the appropriate setting for the right oscillator type and use no more than 1MOhm to bias the oscillator to get it running.