STM32H747XI Discovery board, what does it means disabling digital microphone DOUT

[SylvainFluent]

Hi All,

We are using the STM32H747XI Discovery board and we need to use the onboard microphone to get voice recorded and send it over Ethernet.

From https://os.mbed.com/teams/ST/wiki/DISCO_H747I-modifications-for-Ethernet, to use the Ethernet port, we need to welded/unwelded the following resistances:

• Modify solder bridges and resistor as below (for details, refer to STM32H747I-DISCO board user manual https://www.st.com/resource/en/user_manual/dm00504240.pdf) : 
  • SB21, SB45 and R87 should be opened
  • SB22, SB44, SB17 and SB8 should be closed

From some source, only changing SB8 and SB21 state could be sufficient to make the Ethernet work?

Changing SB8 and SB21 means changing the configuration from STM32H747XIH6 port PC1 is connected to MEMs. digital microphone DOUT to STM32H747XIH6 port PC1 is connected to Ethernet ETH_MDC.

But doing so we disable the digital microphone DOUT, does it makes the microphone onboard not working? What does it implies exactly?

Thanks in advance

[Mike_ST]

Hello,

Please check the schematics available here :

https://www.st.com/en/evaluation-tools/stm32h747i-disco.html#cad-resources

I have not worked with that board, but from what I see in the schematic:

- One configuration uses the STM32H7's SAI4 peripheral to capture the U21 microphone output

- The other uses the WM8994 audio codec chip to capture the U21 microphone output, the audio codec then redirect the stream to SAI1 channel B => you'll have to configure the WM8994 chip using I2C4 to achieve that.

[SylvainFluent]

Thanks for the reply, but this is not what I am looking for. 

But doing so, we disable the digital microphone DOUT, does it makes the microphone onboard not working? What does it implies exactly?

[Mike_ST · Accepted solution]

>> From some source, only changing SB8 and SB21 state could be sufficient to make the Ethernet work?

Maybe Ethernetw will work, but not the digital microphone as the DOUT won't go anywhere.

>> We are using the STM32H747XI Discovery board and we need to use the onboard microphone to get voice recorded and send it over Ethernet.

In this case you need the full configuration:

• SB21, SB45 and R87 should be opened
• SB22, SB44, SB17 and SB8 should be closed

This enable the following configuration I mentionned above:

"- The other configuration uses the WM8994 audio codec chip to capture the U21 microphone output, the audio codec then redirect the stream to SAI1 channel B => you'll have to configure the WM8994 chip using I2C4 to achieve that."

[SylvainFluent]

We have to disqualify STM32H747XI Discovery board as a potential target for our demo as the On Board mic and the Ethernet port cannot be used at the same time and we would have to modify each hardware before sending it to customer.