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PCM1862: Why the data shows 0xFFFF8000

juana peng1
Prodigy 30 points
Part Number: PCM1862

Hi,

A analog Mic is connected to ADC1 L channel as differential input, the data on I2S most of time show 0xFFFF8000. Sometimes data shows 0x00000000.

Is it normal? Please see below picture.

My Settings:

PCM1862 works as slave, Left Justified, Fs=16khz, BCK=64*LRCK=64*Fs=64*16K=1.024Mhz, Mclk=256Fs=256*16K=4.096Mhz.

I measured the clock, all clock's frequencies are correct.

  • 0
    TI__Mastermind 23050 points

    Hi Juana,

    I'm not entirely sure how to interpret the data presented. However this definitely doesn't look like analog microphone data, but seems almost more like a clock signal applied to the analog input instead. I suspect there is an issue with the channel configuration as your clock frequencies seem sufficient to support 2-channels of 32 bit data at 16kHz. By default the ADCs are configured for single-ended inputs so you need to make sure you set this register to differential inputs. You'll also want to make sure you are looking at the correct data output, by default ADC1L and ADC1R are output in 2 channel modes, but this can be configured to output the data in many different ways depending on the input mux and digital mixer settings.

    Best,

    Zak

     

  • 0 in reply to Zak Kaye
    Prodigy 30 points

    Hi,

    Thanks for your feedback.

    Please help review my settings.

    1. My ADC Input Mux setting:

    ADC1L: Page0, Register6, 01010000, VIN1P&VIN1M DIFF; Will connect a analog mic.

    ADC1R: Page0, Register7, 01001100, VINR4[SE]+VINR3[SE]; Will connect FM line in signals.

    2. ADC Output Mix setting:

    (1) Question 1: Is MIX1 for I2S left channel data? MIX2 for I2S right channel data?

    (2) Question 2: How to set Ch1L only for Mix1? Is it to set Ch1L to 0db, and set other channels to -100db? 

  • 0 in reply to juana peng1
    TI__Mastermind 23050 points

    Hi Juana,

    Each mixer can mix data from both left and right channels together. However, by default mix 1 is set to CH1L and mix 2 is set to CH1R. Other channels in the mix are default set to -120dB so as not to interfere. You may also want to verify that your hardware connections match the pins that the internal muxes route to the left and right ADCs.

    Best,

    Zak