Reply by Jim Granville●September 10, 20082008-09-10
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
Reply by Martin Griffith●September 10, 20082008-09-10
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.
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.
Reply by CBFalconer●September 9, 20082008-09-09
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.
--
[mail]: Chuck F (cbfalconer at maineline dot net)
[page]: <http://cbfalconer.home.att.net>
Try the download section.
Reply by Martin Griffith●September 9, 20082008-09-09
On Tue, 9 Sep 2008 10:58:03 -0700 (PDT), in comp.arch.embedded linnix
<me@linnix.info-for.us> wrote:
>On Sep 9, 10:51 am, Martin Griffith <mart_in_med...@yah00.es> wrote:
>> On Tue, 9 Sep 2008 10:43:25 -0700 (PDT), in comp.arch.embedded linnix
>>
>>
>>
>> <m...@linnix.info-for.us> wrote:
>> >On Sep 9, 10:33 am, Martin Griffith <mart_in_med...@yah00.es> wrote:
>> >> On Tue, 9 Sep 2008 09:08:12 -0700 (PDT), in comp.arch.embedded linnix
>>
>> >> <m...@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,
>>
>> >Only if you have better crystals. Those I am looking at are 20 to
>> >25ppm.
>>
>> Have a squint at AN934 ftom ST, it means I can use a cheap xtal, and
>> it can be auto calibrated by the 1PPS from a GPS
>
>With the GPS PPS, there is absolutely no reason to have external clock
>chip. I guess you are operating outside bean counters (cost
>managers).
>
Sadly, I'm the bean counter.
This is a portable thing, GPS will only be used to calbrate once,
after a 24 hour burn in and not fitted on the final unit, which as
you say, would negate the need for a RTC.
>> when I make the
>> boards up>> 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.
>>
>> You left out IMHO :)
>> and that would mean a pot in the circuit, nope
>
>Depending on the uC. Some don't need external components at all, with
>internal clocking. Others (my current target) require one R and one C
>for clocking.
>
>>
>>
>>
>> >> 2) It is SPI protocol, I just hate I2C
>> >> 3) Not made by Maxim
>>
>> >> martin
>>
>> martin
martin
Reply by linnix●September 9, 20082008-09-09
On Sep 9, 10:51 am, Martin Griffith <mart_in_med...@yah00.es> wrote:
> On Tue, 9 Sep 2008 10:43:25 -0700 (PDT), in comp.arch.embedded linnix
>
>
>
> <m...@linnix.info-for.us> wrote:
> >On Sep 9, 10:33 am, Martin Griffith <mart_in_med...@yah00.es> wrote:
> >> On Tue, 9 Sep 2008 09:08:12 -0700 (PDT), in comp.arch.embedded linnix
>
> >> <m...@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,
>
> >Only if you have better crystals. Those I am looking at are 20 to
> >25ppm.
>
> Have a squint at AN934 ftom ST, it means I can use a cheap xtal, and
> it can be auto calibrated by the 1PPS from a GPS
With the GPS PPS, there is absolutely no reason to have external clock
chip. I guess you are operating outside bean counters (cost
managers).
> when I make the
> boards up>> 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.
>
> You left out IMHO :)
> and that would mean a pot in the circuit, nope
Depending on the uC. Some don't need external components at all, with
internal clocking. Others (my current target) require one R and one C
for clocking.
>
>
>
> >> 2) It is SPI protocol, I just hate I2C
> >> 3) Not made by Maxim
>
> >> martin
>
> martin
Reply by Martin Griffith●September 9, 20082008-09-09
On Tue, 9 Sep 2008 10:43:25 -0700 (PDT), in comp.arch.embedded linnix
<me@linnix.info-for.us> wrote:
>On Sep 9, 10:33 am, Martin Griffith <mart_in_med...@yah00.es> wrote:
>> On Tue, 9 Sep 2008 09:08:12 -0700 (PDT), in comp.arch.embedded linnix
>>
>> <m...@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,
>
>Only if you have better crystals. Those I am looking at are 20 to
>25ppm.
>
Have a squint at AN934 ftom ST, it means I can use a cheap xtal, and
it can be auto calibrated by the 1PPS from a GPS when I make the
boards up
>> 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.
You left out IMHO :)
and that would mean a pot in the circuit, nope
>
>> 2) It is SPI protocol, I just hate I2C
>> 3) Not made by Maxim
>>
>> martin
martin
Reply by linnix●September 9, 20082008-09-09
On Sep 9, 10:33 am, Martin Griffith <mart_in_med...@yah00.es> wrote:
> On Tue, 9 Sep 2008 09:08:12 -0700 (PDT), in comp.arch.embedded linnix
>
> <m...@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,
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.
> 2) It is SPI protocol, I just hate I2C
> 3) Not made by Maxim
>
> martin
Reply by Martin Griffith●September 9, 20082008-09-09
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
martin
Reply by linnix●September 9, 20082008-09-09
On Sep 9, 9:26 am, donald <don...@notinmyinbox.com> wrote:
> linnix 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.
>
> Software RTCs as you are suggesting does not keep accurate time in the
> long run.
>
Using the same watch crystal as the chip, you can get same accuracy.
> After a few weeks the time is off by a few seconds.
If you know how much your timing cycle is off, you can adjust it.
> Months or years, its off by minutes.
>
> Standby current is not the only consideration.
>
> donald
>
> PS: Using the DS1307, I found that you can not read the chip without a
> battery connected or VBat grounded. The data sheet was not real clear
> about this, but programming a PIC bit-bang function did not work till I
> connected a battery.