I2C triggers I2S issue

dimitrisTymph Question

Nov 12, 2014 00:00

Hi forum,

I am working on a product that carries an ADAU1761 chip and an external MCU.

The two chips communicate through I2C protocol.

I am witnessing some weird behaviour however:

I am have set my DSP chip to output the I2C data through the ADC_SDATA pin (should be pin no 26 on an ADAU1761 chip).

When streaming music through an evaluation board then the pin 26 spits out digital audio data as it should.

When I am working on the actual product then the output is always low.

I tried deactivating the I2C communication between the MCU and the DSP so I can debug the DSP on the board.

The ADC_SDATA output was firing digital audio nicely again.

Activated I2C communication again between MCU and DSP, streamed music, the ADC_SDATA is always low again.

For some reason, it seems that the I2C is affecting the I2S output.

In my DSP design there is no control over the digital output. I just route the signal to output to DIG0 and DIG1 as well as to DAC0 and DAC1.

Any idea if any settings of the DSP chip could be causing such a behaviour?

I am quite puzzled. I don't see how the I2C could affect the I2S pins...

Any suggestion that could lead me to the correct direction is welcome

thank you

Dimitris

Audio Signal Processors

SigmaDSP Audio Processors

adau1761

782004ec310de3d7e337dbc2ee8b762a.png-620x309.png

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JohnTo Reply

Nov 13, 2014 00:00

Hello Dimitris,

When you say that I2C communication affects the I2S pins, does this happen only after the ADAU1761 on-chip registers are programmed from default state? If so, is it possible to give the values of all on-chip registers? Either providing the SigmaStudio project or showing the download values from the SigmaStudio capture window would also help.

What is the value of the Serial Port Pad Control register (address 0x402D)?. Do you enable the pull-down resistor in the ADC_DATA line (bits #7:6)? The default value is "None" (pull-ups/pull-downs disabled). I am wondering if this is affecting the output on the pin if it is changed from the default.

-JT

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dimitrisTymph Reply

Jan 17, 2015 00:00

Hi John,

thank you for your reply.

I managed to solve the issue, the DSP was not the problem.

The MCU was disabling the I2S right after initialisation of the DSP.

I was careless, sorry to have you bothered with this one.

thanks,

Dimitris

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