GPIO11/GPIO12 Low Voltage

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  • September 8, 2015 at 2:28 pm #9115
    Zack Freedman
    Participant

    We’re having problems with low logic-high levels on the GPIO11 and GPIO12 pins of our MTSMC-H5-U modules.

    The datasheet specifies a minimum logic low of 2.9V, but when set high using the filesystem driver or mts-io, these pins output only about 0.47V.

    The GPIO pins feed directly into a TI TXB0108 logic-level translator, which shifts them to 5V logic. The TXB0108 has 4kΩ nominal input and output impedance, and is adequately bypassed.

    The problem can be replicated with and without 100kΩ pullups or pulldowns on the level translator’s input or output.

    Other pins seem unaffected – GPO1-4 output the specified ~2.7V when connected to other pins of the same TXB0108 without pullups or pulldowns.

    September 8, 2015 at 2:49 pm #9116
    Zack Freedman
    Participant

    I just tested again with a similar module in the OEM devboard, and it seems to be outputting the correct logic levels.

    Are specifications available for the drive strength or other electrical parameters of the GPIO pins? Could userspace or kernel-level code be accidentally switching them into a high-impedance input mode?

    September 8, 2015 at 3:40 pm #9117
    Zack Freedman
    Participant

    More testing shows that GPIO11 and 12 sag when driving anything with more than 40kΩ input impedance. Is there any way to increase this? 83µA drive strength is excessively low.

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