Lpc2000

Just as a follow up, in case someone runs into this problem:

The answer to my question is yes, apparently you need to have the Vcc 
switching in place to run the RTCK off of Vcc when Vcc is present, and Vbat 
when Vcc is not present.  If Vbat is used to power the RTC when Vcc is 
present then the clock will do some strange things.

-- Sean

At 22:51 1/30/2006, you wrote:
>Tom:
>
>Thanks for the code!
>
>Is it *necessary* to have the switching in place (as opposed to use leaving
>the lithium to power the RTC all the time)?  Just curious.
>
>-- Sean
>
>At 22:24 1/30/2006, you wrote:
> >Sean wrote:
> >
> > >Hello everyone,
> > >
> > >I've got a bit of a strange problem with the RTC in my setup.  I have a
> > >dedicated lithium battery going to the Vbat pin to power the RTC, and it
> > >usually works fine, however periodically the clock changes to an invalid
> > >value and stops running.  Usually this value is something like "Year:129
> > >Month:00 Day:16 Hour:02 Min:09 Sec:08", and unless I reset the RTC to a
> > >valid value it stops running.  This will usually happen after several 
> hours
> > >of Vcc absent (i.e. device powered off) or after a day or two running
> > >constantly.  Nothing else is disrupted.  I have a 3.6V lithium running
> > >through a diode which drops the voltage at the pin down to 3.165V when Vcc
> > >present and to 3.232V when Vcc absent (implying that more current is drawn
> > >when the micro is powered on??)
> >
> >Diode switching is needed to maintain the Vbat when Vdd (3.3v main) is
> >absent and to switch over to the battery when Vdd disappears.  It sounds
> >like you have that working?  It will take two diodes (1N4148A) and a
> >resistor (560ohm) to do this properly.  Cathodes of both diodes go to
> >Vbat line, anode of one diode goes to Vdd, anode of other diode is
> >series with 560ohm to positive terminal of Lithium cell.
> >
> >This is half the solution, the hardware half.  I found that my clock
> >would also "explode" on occasion and seemingly at random.  The solution
> >I took was a bit more aggressive in the software.  Study my clock
> >routines, especially awakenClock() and sleepClock().  Essentially, when
> >the clock registers are not needed, they are "disconnected".
>
>
>
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