I2C SDA not going to zero! 3.3V --> 1.14V !


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  1. #1
    Join Date
    Mar 2006
    Location
    China
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    266

    Default Re: I2C SDA not going to zero! 3.3V --> 1.14V !

    Should? maybe

    Will? Only a deep dive into the datasheet can be sure of that.

    PIC18F26J53 har PPS (periphial pin select or how it is spelled, menaing you can re-route HW functions to different pins)

    So what PIN on the device and what PORT-id do you use?

    I would not bet that all pics always gets all registers set up exactly the same everytime.. so there might be a conflict that is because of a register setting.

    Before I start pulling components I would advise you to give us more details about the device setup and configuration...and PPS register settings

  2. #2
    Join Date
    Oct 2005
    Location
    Sweden
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    Default Re: I2C SDA not going to zero! 3.3V --> 1.14V !

    Hi,
    Have you verified the value of the pullup resistor? Perhaps it's 10ohms instead of 10k or whatever it's supposed to be. The PIC can only pull so hard on the pin, if the pullup is too stiff it won't be able to get it all the way to Vss.
    I was going to suggest to lift the pin in question and measure directly on the pin but with a QFN that won't be easy. Make sure you measure from the pin in quesion to adjacent pins, perhaps there's a solder bridge under the chip.

    /Henrik.

  3. #3
    Join Date
    Sep 2009
    Posts
    755

    Default Re: I2C SDA not going to zero! 3.3V --> 1.14V !

    Put your pin to input, then measure current between ground and pin.
    IF current is few mA THEN pic is problem
    IF current is much bigger THEN
    Remove pull up
    Measure again
    ENDIF
    IF any current exist THEN
    Problem is in sensor or pcb
    Remove sensor
    measure current.
    IF any current exist THEN
    pcb have short
    ELSE
    Problem is in sensor
    END IF

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