Richard Tenney

Real time Counter S08RTCV1 accuracy

Discussion created by Richard Tenney on Feb 9, 2010
Latest reply on Feb 12, 2010 by Richard Tenney

In discussing the real time counter (S08RTCV1), the MC9S08SH32 reference manual says "Because the 1-kHz clock source is not as accurate as a crystal, ...."  However, the block diagrams all show the 1-kHz internal low-power oscillator (LPO), a potential clock source for the RTC module, with leads to the external crystal.


Does this mean that if there is an external crystal, the RTC can use the LPO as its clock source and that the LPO can be synced to the crystal, which in our design will be 32.768 kHz, to produce a crystal-controlled time base?  Our goals are

  1) to generate 10ms interrupts and

  2) provide reasonably accurately timed intervals lasting up to 100 hours. 


I find the documentation less than clear on this point.  Can anyone enlighten me?



    - Richly