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PICList Thread
'Time Stamping'
2000\05\19@091034 by Andy Stubbins

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I am working on a project that incorporates the pic16f876. Part of the project involves data logging quite a large amount of data over a period of time and the data requires an accurate time stamp for evaluation purposes. It would be appreciated if anyone has any suggestion on the time stamping.
Many Thanks Andy Stubbins

2000\05\19@092455 by D Lloyd

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part 0 1599 bytes content-type:application/octet-stream;Hi,

What is the resolution of the timestamping required? If one second, you could
employ a four byte timestamp based on the UTC "days since 1970" system. Clearly,
this 4 byte system might be a bit excessive as it allows for about 100 years of
dates.

Microsoft C++ supports conversion functions, as does Excel, so converting the
timestamps is relatively easy to do.

Just a suggestion,

Dan



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Please respond to pic microcontroller discussion list <.....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU>

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cc:    (bcc: Dan Lloyd/GBPTD/ABB)
Subject:  Time Stamping

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I am working on a project that incorporates the pic16f876. Part of the project
involves data logging quite a large amount of data over a period of time and the
data requires an accurate time stamp for evaluation purposes. It would be
appreciated if anyone has any suggestion on the time stamping.
Many Thanks Andy Stubbins






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Content-Disposition: attachment; filename="pic26545.pcx"

Attachment converted: creation:pic26545.pcx (????/----) (00014C30)

2000\05\19@114029 by Quitt, Walter

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I go two routes.  One is a Dallas clock.  The other is to
get time off a GPS serially.  By using the GPS 1PPS signal
I can sync the processor to that create time stamps.  That's
the simple answer.  It is a bit more complicated in code.

GL,
Walt...

-----Original Message-----
From: Andy Stubbins [.....andyKILLspamspam.....STUBBINSR.FREESERVE.CO.UK]
Sent: Friday, May 19, 2000 5:59 AM
To: EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU
Subject: Time Stamping


I am working on a project that incorporates the pic16f876. Part of the
project involves data logging quite a large amount of data over a period of
time and the data requires an accurate time stamp for evaluation purposes.
It would be appreciated if anyone has any suggestion on the time stamping.
Many Thanks Andy Stubbins

2000\05\19@234656 by Ramana

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Hi,
I am using the PIC as replacement for a dallas clock chip because I can
integrate some other functionality to it. Mine ia also a data logging
type. I am using the PIC also to monitor the changes in any Analog
signal to wake up the main processor which is sort of power hungry when
not in sleep mode.

So the point is why don't you use the timer in PIC to maintain a real
time clock. Is there anything I am mising
rgds
ramana

{Original Message removed}

2000\05\20@122140 by Dan Michaels

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Ramana wrote:
....
>So the point is why don't you use the timer in PIC to maintain a real
>time clock. Is there anything I am mising
>rgds
>ramana
>

The PIC internal timer makes a fine RTC, if the xtal frequency is
chosen correctly [some power of 2], and as long as updating the clock
and data acquisition don't louse up each other's timing.

Absolute accuracy is always a problem, as even a +/-50 PPM xtal
translates into ~4 sec error per day.

Also, you might check out the 2nd gen PICs, like 16C73/74. They
have a 2nd internal oscillator wired to pins C0 & C1, which can
be used with a 32 Khz watch xtal, even while the main oscillator
runs at 20 Mhz [whatever]. However, I have never heard tell of
anyone actually using it. Guys????

- Dan Michaels
Oricom Technologies
http://www.sni.net/~oricom
==========================

2000\05\20@213154 by Andrew Warren

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Dan Michaels <PICLISTspamspam_OUTMITVMA.MIT.EDU> wrote:

> 16C73/74 .... have a 2nd internal oscillator wired to pins C0 &
> C1, which can be used with a 32 Khz watch xtal, even while the main
> oscillator runs at 20 Mhz [whatever]. However, I have never heard
> tell of anyone actually using it. Guys????

   I've used it, Dan; it works fine as a real-time clock.

   -Andy


=== Andrew Warren - @spam@fastfwdKILLspamspamix.netcom.com
=== Fast Forward Engineering - San Diego, California
=== http://www.geocities.com/SiliconValley/2499

2000\05\22@095327 by Dan Michaels

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I wrote:
>
>The PIC internal timer makes a fine RTC, if the xtal frequency is
>chosen correctly [some power of 2], and as long as updating the clock
>and data acquisition don't louse up each other's timing.
....

BTW, more correctly I should have said the xtal can be chosen as an
*integer multiple* of a power of 2. For instance, 4,915,200 is a std
xtal frequency, and is 75*256*256. Here, timer T0 could be set to
interrupt after reaching max count, and a s.w. variable would count
down 75 times ---> 1 sec.

best regards,
- Dan Michaels
Oricom Technologies
http://www.sni.net/~oricom
==========================

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