Effect of GPIO input

[yoshida_satoru]

I plan to use the i.MX RT 1010.
Use SAI1 to create the following circuit.

I would like to create a combined SYNC and DATA1 output using this circuit.
When outputting SYNC, set DATA1 to GPIO input via SW_MUX_CTL_PAD_XXX SW MUX Control Register.
When outputting DATA1, set SYNC to GPIO input via the SW_MUX_CTL_PAD_XXX SW MUX Control Register.

I would like to know the external effects of GPIO inputs.
Since this is input, I don't think it will have any impact, but is that correct?

[mayliu1]

Hi @yoshida_satoru ,

Thank you so much for your interest in our products and for using our community.

I'm sorry that I don't  quite understand your design. Are you trying to use the function of the SAI module? If so, SYNC clock and Tx data  should not be connected.

If I don't understood your question correctly, please provide me with more information so that I can better support you.

Wish it helps you.
If you still have question about it, please kindly let me know.

BR

MayLiu

[yoshida_satoru]

thank you for your reply.
Let me provide some additional explanation.

I want to output PCM and DSD from the SAI1 and input it into an Audio DAC.
For PCM, use SAI1_TX_BCLK, SAI1_TX_SYNC(LRCK), and SAI1_TX_DATA0.
SAI1_TX_DATA1 is not used when playing PCM.
For DSD, use SAI1_TX_BCLK, SAI1_TX_DATA0, and SAI1_TX_DATA1.
SAI1_TX_SYNC (LRCK) is not used when playing DSD.

Another thing I would like to do is connect the SAI1 directly to an Audio DAC.
The Audio DAC has a shared input pin for SAI1_TX_SYNC (LRCK) and SAI1_TX_DATA1.
Do not use PCM and DSD at the same time.

To achieve this, we are considering the following circuit:

I would like to use SAI1_TX_SYNC (LRCK) and SAI1_TX_DATA1 connected in the circuit exclusively.
To achieve this, we are considering setting the functions of unused pins to GPIO.
The function of the pin is to change the MUX_MODE bit of the SW_MUX_CTL_PAD_XXX SW MUX Control Register.
In addition, set the GPIO to input to eliminate any external influence.

It is also possible to physically switch between SAI1_TX_SYNC (LRCK) and SAI1_TX_DATA1 using a switch circuit or the like.
However, in order to keep costs down, I would like to reduce the number of ICs, such as switch circuits, so I am considering the above circuit and implementation.

I have a question.
I would like to achieve a shared output for SAI1_TX_SYNC (LRCK) and SAI1_TX_DATA1.
Is it possible to achieve shared output with the circuit and implementation shown above?

[mayliu1 · Accepted solution]

Hi @yoshida_satoru ,

Thanks for your updated information.

I understood your design concept from your circuit diagram.

I know that you want to set the functions of unused pins to GPIO ,and configure GPIO pin as inputs with the aim of eliminating any external influences. However, this method may not very reliable for your entire audio system.

Regarding you said before "It is also possible to physically switch between SAI1_TX_SYNC (LRCK) and SAI1_TX_DATA1 using a switch circuit or the like."

I agree with your point, I suggest using a low cost switch might be the most straightforward and reliable solution.

Wish it helps you.
If you still have question about it, please kindly let me know.

BR

MayLiu