I2S connection between Iridium modem and PicoCore iMX8MP

  • Hey,

    I need to connect the Iridium modem's I2S to the SAI2 of the PicoCore iMX8MP.

    The modems pins are:

    I2S_SPKR_WS (output; I2S word select)

    I2S_SPKR_SCK (output; I2S primary clock)

    I2S_SPKR_SD (output; audio output data)

    I2S_MIC_SD (Input; audio input data; 100k pull-down)

    Pins are 3.3V TTL

    Here the modem dev manual description:

    The Iridium Certus 9770 has a digital audio interface that supports up two independent voice


    Digital audio samples for voice calls are transferred over two I2S data lines: I2S_MIC_SD for

    digital audio going to the Iridium Gateway and I2S_SPKR_SD for digital audio coming from the

    Iridium Gateway. Each data line operates at a serial clock transfer speed of 512 kHz passing

    audio samples using a common clock (I2S_SPKR_SCK). Each interface also transfers audio

    samples using a common select signal (I2S_SPKR_WS) at a rate of 8000 samples per second

    and 16-bit samples.

    Within each I2S data line, two ‘audio lines’ are supported using the left and right channels of the

    I2S interface. Digital samples for audio line #1 are transferred using the I2S_SPKR_WS low word.

    Digital samples for audio line #2 are transferred using the I2S_SPKR_WS high word.

    Would this interface be compatible and if yes, what pins should match on the PicoCore side?


  • See HW-Manual chapter 4.8 page 27/28.

    You can use AUDIO_A or AUDIO_B interface.

    AUDIO_A is only available if the audio codec is not installed.

    AUDIO_B is 1.8V, so a level shifter is needed.

    The audio format is configurable in software, so the modem should work with the PicoCore.

    connection is as follows:



    RXD0 -> SPKR_SD

    TXD0 -> MIC_SD

    F&S Elektronik Systeme GmbH
    As this is an international forum, please try to post in English.
    Da dies ein internationales Forum ist, bitten wir darum, Beiträge möglichst in Englisch zu verfassen.