Lpc2000

--- In lpc2100@yahoogroups.com, "Igor Janjatovic" <kodrat@p...> wrote:
> > This means that the contents of the clock are a bit fragile, really -
> > suggesting it will be better used as a local 'cache' of an external
> > seperately-clocked real time clock unit that's slow to access (I2C or
> > similar), loaded from it during startup or return from power down mode
> > after setting up the PLL and the RTC divider registers. Unless you
have
> > a setup that's rarely reset and never put into power down mode,
it's not
> > all that useful, as I see it.
> 
> I have this low power design that I'm working on and I'm using
PCF8593 I2C
> RTC with 32.768kHz clock. PCF will take only 1uA so I planned to put
MCU in
> Power Down most of the time. When running, MCU will take time and
date from
> PCF and use it with its own integrated RTC just as you suggested.
PCF will
> be updated only when time or date is changed by user.
> 
> > Anyone else had any thoughts about it? It would have been nice if they
> > provided an external 32,768Hz clock input pin to run the RTC off
of when
> > the MHz oscillator was down!
> 
> Looking at LPC spec for the first time that's what I expected. Later,
> looking at User Manual was very... well... disappointing. Who needs
RTC with
> 20mA current consumption (when in Idle mode)?????
> 
> > On the other hand, it occurs to me that the PLL seems amply capable of
> > producing processor clock frequencies far in advance of the rated
60MHz
> > - overclocking! How soon before we see huge copper heatsinks with fans
> > for LPC2100s, eh? ;-)
> 
> Few days ago someone said that they used overclocked LPC without any
> problems...
> 
> Regards,
> Igor

Hi,

I wondered as well why there was no 32 kHz input for the LPC. This
question was also asked at the Philips training that I participated.
The answer was along the lines of "there are applications that are
always connected to AC and they need to track time" well I guess that
is true. "Also the are other applications that need to go into power
down for minimum power and still should track time with some uAs of
power. Unfortunately this can not be done with the current
implementation of the LPC."  Guess that is true as well. The proposed
solution was to use a small LPC900 device, e.g. an 8-pin micro that
would have a RTC / System Clock. Looked into this a little and it can
definitely be done. Providing 32 kHz to such an LPC900 device and
using the 1k Flash to generate a real time-of-day timer is not hard to
do. According to my information the LPC900 devices would be lower cost
 than the PCF 8593 and more flexible but on the downside it would
require some 10s of uAs instead of 1 uA. If battery driven that can
make all the difference.

You may come up with your own conclusions ;-)

Cheers, Bob