Peter Koblauch

MC9RS08KA4/KA8 and watch crystal for RTC, how low will it go

Discussion created by Peter Koblauch on Mar 17, 2008
Latest reply on Mar 18, 2008 by Peter Koblauch
Hello,
 
 I am trying to understand if the new KA4/KA8 devices can be used as low power
 real-time clock and how low it will go power-wise.

  The datasheet seems to hint that it will go down to 3.6uA using a 1MHz external clock,
  I think being divided down by some factor (or divisor really), bypassing the FLL, which
  is turned off anyway, and clocking  the 16 bit timer, that eventually flows over and generates
  an interrupt, waking up the MCU from sleep/stop/wait. I'm not sure of the terminology here.
  (neither is the datasheet, which does not seem to always make a clear distinction between
  crystal, oscillator, and (external) clock)

The 3.6uA which the datasheet seems to indicate, would  surprise me (too low at that high a frequency),

  We''ll really I am interested in the case where you would use a 32.768 watch crystal.
  This should be even (much) better, but I do not feel confident that I interpret
  the datasheet right (I'm used to TI's msp430).

Being new to Freescale MCUs I'd appreciate any help or pointers.


thanks for reading this far,
  Peter


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