BOB RITCHEY

MCF51QE Clocking Questions

Discussion created by BOB RITCHEY on Apr 15, 2008
Latest reply on Feb 25, 2009 by Jorge Andres Reyes Alvarez
Hi,
I am new to Freescale, used MSP430, but am switching my entire product line over.  I am just getting started on the MCF51QE family on a new design.  I am a bit confused about the best way to configure the ICS.  I need to run my timers at 4MHz.  I would like to run the CPU at the highest rate possible.  I need an accurate clock so I am going to run an external resonator.   One thing that I miss, unless I am wrong, is the oscillator failsafe mode of the MSP430.  I see no provision in the MCF51QE to failsafe to the DCO if the external oscillator quits.  Did I miss anything?  It seems that if I use a 4MHz reference resonator (which I already use in quantity) I will need to run the CPU at 32MHz in order to be able to divide this down for the timers to run at 4MHz since there are only binary prescalers for the timers.  Thanks for any feedback on these issues.

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