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Best way to clock MCU for precision timing application

Question asked by Matthew Smith on Mar 4, 2013
Latest reply on Mar 11, 2013 by Matthew Smith

I am working on a number of clock designs (as in things that tell the time,) all of which will be based around and MC9S08AC128. The timing source will be a DS32KHZ 32768 Hz TCXO.


Whilst I can clock the MCU from the DS32KHZ, feeding into EXTAL, and then deriving internal clocks from the FLL (or so I understand,) for the purposes of doing something every second (32,768 'ticks' of the oscillator,) is it best to do this, or use some other clock source for the device (such as internal) and just have the DS32KHZ driving an external interrupt? I assume there must be some sort of best practice in this type of scenario.


My goal is for the devices to keep good time - I'm not fussed about whether displays might refresh a few milliseconds early or late - as human eyes will never notice. (But they will notice how far the things drift from atomic time, over time.)


In case it has any bearing on the matter, firmware will be created using CodeWarrior, making as much use of Processor Expert as possible.