RTC timing issue

Discussion in 'General Electronics Chat' started by aamirali, Jun 26, 2013.

  1. aamirali

    Thread Starter Member

    Feb 2, 2012
    415
    1
    I am using RTC with I2c specs at 100Khz. Now specs says that min Tlow = 4.7us & min Thigh = 4us.

    Now freq = 1/ (Tlow + Thigh) = 1/(4.7 + 4) = 115Khz while this specs is for max 100Khz clk.

    What is this error
     
  2. MrChips

    Moderator

    Oct 2, 2009
    12,440
    3,360
    What error?

    Best to state the RTC part number.
     
  3. aamirali

    Thread Starter Member

    Feb 2, 2012
    415
    1
    No rtc error, but specific to I2c spec error.

    Like I2c specs define Max scl freq = 100Khz.
    while with tlow & Thigh, its comes out to be 114khz max.
     
  4. MrChips

    Moderator

    Oct 2, 2009
    12,440
    3,360
    Ok then, make min Tlow = 5us and min Thigh = 5 us.
    Does that make you happier?
     
  5. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,386
    1,605
    No error, just interpretation.

    Obviously if you have a minimum Tlow you can't also run Thigh at it's minimum and also meet the frequency rate.

    There's also a transition time between low and high not included in your frequency calculation.
     
  6. aamirali

    Thread Starter Member

    Feb 2, 2012
    415
    1
    thanks ErnieM.<br />
    <br />
    Are you talking about tr &amp; tf. If yes they should be minimum &amp; in datasheet there min value is not defined &amp; there max value is defined roulette
     
    Last edited: Oct 2, 2013
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