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ST semi RTC M41T94

Started by Martin Griffith September 8, 2008
On Sep 10, 12:07 am, CBFalconer <cbfalco...@yahoo.com> wrote:
> linnix wrote: > > Martin Griffith <mart_in_med...@yah00.es> wrote: > > ... snip ... > > >> 1) it can be trimmed to 5ppm accuracy, > > > Only if you have better crystals. Those I am looking at are 20 to > > 25ppm. > > >> the rest of the system takes 2A peak for the display. > > > I would consider such a chip if it's standby current is much less > > than the active current of my target uC of 0.9mA. Otherwise, > > there is no point in adding the chip. > > >> There is a possibility of jamming the RTC to a GPS every couple > >> of hours > > > Then a RC timing loop is good enough. > > Hah. Now we know your opinion is worthless. Try it.
Sure, I withdraw my opinion then. I got the wrong impression that GPS is available for synchronizations every couple of hours, which is not the case after the OP clarify it. My opinion is only as good as known fact at the time.
> > -- > [mail]: Chuck F (cbfalconer at maineline dot net) > [page]: <http://cbfalconer.home.att.net> > Try the download section.
On Tue, 9 Sep 2008 19:54:44 -0700 (PDT), in comp.arch.embedded linnix
<me@linnix.info-for.us> wrote:

>On Sep 10, 12:07 am, CBFalconer <cbfalco...@yahoo.com> wrote: >> linnix wrote: >> > Martin Griffith <mart_in_med...@yah00.es> wrote: >> >> ... snip ... >> >> >> 1) it can be trimmed to 5ppm accuracy, >> >> > Only if you have better crystals. Those I am looking at are 20 to >> > 25ppm. >> >> >> the rest of the system takes 2A peak for the display. >> >> > I would consider such a chip if it's standby current is much less >> > than the active current of my target uC of 0.9mA. Otherwise, >> > there is no point in adding the chip. >> >> >> There is a possibility of jamming the RTC to a GPS every couple >> >> of hours >> >> > Then a RC timing loop is good enough. >> >> Hah. Now we know your opinion is worthless. Try it. > >Sure, I withdraw my opinion then. I got the wrong impression that GPS >is available for synchronizations every couple of hours, which is not >the case after the OP clarify it. My opinion is only as good as known >fact at the time. > >> >> -- >> [mail]: Chuck F (cbfalconer at maineline dot net) >> [page]: <http://cbfalconer.home.att.net> >> Try the download section.
FWIW this is what I'm working on http://www.medinatimecode.es/babyslate.html martin
Martin Griffith wrote:
> On Tue, 9 Sep 2008 09:08:12 -0700 (PDT), in comp.arch.embedded linnix > <me@linnix.info-for.us> wrote: > > >>On Sep 8, 7:19 am, Martin Griffith <mart_in_med...@yah00.es> wrote: >> >>>I'm waiting for a couple of M41T94 real time clock chips to arrive, so >>>I'm scribbling some 8052 C code in advance. It's an SPI ic. >>> >> >>My question is why would you need such a chip and not implement the >>clock function in your micro? Standby current of 1.4mA and active 2mA >>is not exactly low power either. > > Mainly > 1) it can be trimmed to 5ppm accuracy, the rest of the system takes 2A > peak for the display. There is a possibility of jamming the RTC to a > GPS every couple of hours > 2) It is SPI protocol, I just hate I2C > 3) Not made by Maxim
NXP have a couple of SPI RTC's, but they do not seem to be widely stocked yet. The PCF2123 sounds interesting, but it is now 3 months since their press release, and still no data ?! -jg