TDM 4 mode on ADAU1361: filling up all 4 slots from input

Hello usaghi-2,

There are only two ADC converters in this part so it is only capable of outputting two channels on the digital port. 

This part is the codec section of the ADAU1761 so it is a very similar part and has similar capabilities. With the ADAU1761 there is a DSP, In the DSP you can develop more signals by processing the outputs of the two ADC. With that part you can send more channels of data to the serial ports. You can send up to 8 channels and receive up to 8 channels. You can also receive 8 channels into the DSP core then send them out the digital port and by doing that daisy chain several channels using several DSPs. However, the codec section only has two ADCs and two DACs. So what you are seeing is the capability of more channels if you had the DSP. The serial port can still be setup for more channels but there is no way to actually put data into them. The "code" used to develop the two parts are the same. 

Also, this part was designed a long time ago and early in the development of TDM streams. Back then one of the ways to do TDM is by using a left/right clock and having the two left channels when the clock is low and the two right channels when the clock is high. So this is why there is one slot filled and one empty when doing TDM-4. Because the second stereo pair is empty. 

I hope this helps. 

Dave T

Hello usaghi-2,

There are only two ADC converters in this part so it is only capable of outputting two channels on the digital port. 

This part is the codec section of the ADAU1761 so it is a very similar part and has similar capabilities. With the ADAU1761 there is a DSP, In the DSP you can develop more signals by processing the outputs of the two ADC. With that part you can send more channels of data to the serial ports. You can send up to 8 channels and receive up to 8 channels. You can also receive 8 channels into the DSP core then send them out the digital port and by doing that daisy chain several channels using several DSPs. However, the codec section only has two ADCs and two DACs. So what you are seeing is the capability of more channels if you had the DSP. The serial port can still be setup for more channels but there is no way to actually put data into them. The "code" used to develop the two parts are the same. 

Also, this part was designed a long time ago and early in the development of TDM streams. Back then one of the ways to do TDM is by using a left/right clock and having the two left channels when the clock is low and the two right channels when the clock is high. So this is why there is one slot filled and one empty when doing TDM-4. Because the second stereo pair is empty. 

I hope this helps. 

Dave T

Hello Dave,

Thank you very much for your answers and explanations.

Best Regards,