huang tuchen

clock question of MC9S12XS128

Discussion created by huang tuchen on Oct 15, 2009
Latest reply on Oct 16, 2009 by huang tuchen

I developed a board based on MC9S12XS128 and I used a 16MHz external oscillator to drive the MCU.

 

In the databook(MC9S12XS256RMV1.PDF) it's said that the external clock should be 1.8V level because the VDDPLL=1.8V from internal regulator and the maxium value is VDDPLL+0.3=2.1V.

 

At first I used 3.3V to power the external oscillator ,i.e. the clock was 3.3V level, but I found that the clock could not drive the MCU and the MCU went into selfclock-mode after reset. When I changed the power for the external oscillator from 3.3V to 5V it works properly.

 

So I am confused. According to the datasheet even the 3.3V exceed the maxium value. But how to explain the problems I meet?

 

Thanks

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