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'[EE]: DS1307 communication(?) problem'
2004\03\30@130931 by Edson Brusque

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Hello,

    I have a circuit with a PIC18F452 and a DS1307 among other components.

    When the PIC is showing current time on an LCD (it reads the
current time from the DS1307 each second), sometimes the display shows
00:00:00 (zero hours, zero minutes, zero seconds) for a reading and then
returns to the correct time.

    It seens there's a communication problem between the PIC and the
1307. This problem was drastically reduced with the use of a 100nF
ceramic cap between pins 4 and 8 (supply) of the DS1307 but it's still
there.

    Someone have seen this before? Is the DS1307 so sensible to noise
on it's supply pins?

    Thank you very much,

    Brusque
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Edson Brusque                     C.I.Tronics Lighting Designers Ltda
Research and Development                   Blumenau  -  SC  -  Brazil
http://www.suporte.ind.br/ryan/netiqueta.htm     http://www.citronics.com.br
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2004\03\31@144355 by Paul Hutchinson

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>-----Original Message-----
>[.....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU]On Behalf Of Edson Brusque
>Sent: Tuesday, March 30, 2004 1:08 PM
>
>     I have a circuit with a PIC18F452 and a DS1307 among other components.
>
>     When the PIC is showing current time on an LCD (it reads the
>current time from the DS1307 each second), sometimes the display shows
>00:00:00 (zero hours, zero minutes, zero seconds) for a reading and then
>returns to the correct time.
>
>     It seens there's a communication problem between the PIC and the
>1307. This problem was drastically reduced with the use of a 100nF
>ceramic cap between pins 4 and 8 (supply) of the DS1307 but it's still
>there.
>
>     Someone have seen this before? Is the DS1307 so sensible to noise
>on it's supply pins?

There are some sensitive analog circuits in the DS1307 so, I consider a
100nF bypass capacitor mandatory. That said, I don't think I've seen poor
bypassing cause the problem you describe.

I have seen this symptom and it was caused by one of these three problems (I
can't remember which one).
1. VBat terminal floating or grounded, it must be powered.
2. Running I2C at > 100kHz (DS1307 is spec'd 100kHz max.).
3. Noise on the I2C bus, fixed by using 10K pull-ups.

Hope this helps,
Paul

>     Thank you very much,
>
>     Brusque

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