Questions for ADAU1787 configurations for Audio Serial Data communication

Dears,

My goal is to complete the following signal flow with external BCLK, LRCK @ 48KHz

(1) ADAU1787 ADC => I2S_Data_Output

(2) I2S_Data_Input => ADAU1787 DAC

In order to check the configurations, I shorted the I2S_Data_Out & I2S_Data_In.

As original expectation, I expected the audio input from ADC can transfer to DAC. But I can not hear the sound from the left channel.

The followings are my experiments

(1) STP0_OUT_ROUTE0 = ADC2 / STP1_OUT_ROUTE0 = ADC3

DAC0_ROUTE = SAI0_00 / DAC1_ROUTE = SAI0_01

=> There's no sound from left channel

(2) STP0_OUT_ROUTE0 = ADC2 / STP1_OUT_ROUTE0 = ADC3

DAC0_ROUTE = SAI0_01 / DAC1_ROUTE = SAI0_01

=> There's still no sound from left channel

(3) STP0_OUT_ROUTE0 = ADC2 / STP1_OUT_ROUTE0 = ADC3

ASRC0_ROUTE = SAI1_00 / ASRC1_ROUTE = SAI1_01

DAC0_ROUTE = ASCRI0 / DAC1_ROUTE = ASCRI1

=> Correct

Why do step2 failed?

Why do step3 can fix the situation?

Must it need to use ASCR whether in input or output side

Thanks a lot.

ADAU1787

Integrated/Special Purpose A/D Converters

Audio CODECs