ADAU1701 I2S interface problem
Hello,
I need to connect a bluetooth module as digital audio input to our ADAU1701 using the I2S interface.
The problem is that the BT module doesn't offer an MCLK signal. In the datasheet of the module I found this section however:
"In addition to the I2S signals mentioned above, many external codec ICs require a high frequency master clock (MCLK). Typically this clock is a multiple integer of the sampling rate fs, e.g. 128 fs / 192 fs / 256 fs / 384 fs / 512 fs and so forth. Unfortunately, BTM51x cannot provide such MCLK signal. We recommend you select an external codec IC which has the capability of creating the MCLK internally from the bit clock signal (SCK). Such capability is referred to as “PLL” (phase locked loop) or “FLL” (frequency locked loop) functionality of the codec device."
I read that the ADAU1701 has PLL but I couldn't get this to work. On this board I found topics saying that the ADAU1701 needs the MCLK anyhow.
What is correct now? Is there any way I can get this configuration to work?
Audio Signal Processors
SigmaDSP Audio Processors
adau1701
Hi,
Unfortunately, the PLL inside the ADAU1701 will not run from an LRCLK signal, only from an MCLK. I do not know of any external PLL ICs that will generate a 256x output.
Our automotive codec products have a PLL that will run from LRCLK, please check out the AD1938/39 parts. This does not remove your need for a DSP, and the AD1940 might be the easiest DSP that is digital I/O.
Please let me know if this makes sense and if you have any other questions.
Best regards,
Coleman
Thanks for your fast reply!
Unfortunately we have a board ready designed with your ADAU1701 and only need to add the bluetooth functionality. So no way to change the ADAU1701.
Since I2S does not mandatory need MCLK is there any way to run the ADAU1701 only with the LRCLK, BCLK and Data? I know some devices allow this. The BTM always runs at 44.1kHz if that helps in any way.
Is there any way that the bluetooth IC can act as a slave port? You could set the ADAU1701 to be a master, driving BCLK and LRCLK to the BT module to clock the data out. Otherwise, the ADAU1701 requires an MCLK that needs to be synchronous (but not necessarily phase coherent) with the LRCLK and BCLK signals. If you run the ADAU1701 from a crystal, for MCLK, and drive the LRCLK and BCLK ports with asynchronous clocks from the BT, the edges will cross and you will have some unpredictable artifacts.
In fact the BT module has I2S slave function. I think it was intended in case the BT module acts as a I2S receiver. But maybe this can work as an transmitter as well. I think it's worth a try.
Since I only have EVAL-ADAU1701MINZ boards here to try that out I will have to modify one of them. I looked at the schematics provided. The way I understand it I have to remove (bridge) the resistors R33 + R14 and instal jumper connectors instead of LEDs D4 and D6.
Then I can get the master clocks LRCLK and BCLK from MP10+11 and input the serial data to MP0 (SDATA_In on J7)?
I'm just aksing since I'm more of an audio guy. This is mostly new for me.
But really thanks so far. If this works it might save me a lot of work.
Yes, you have a good plan here. You will be able to get this system running with your proposed configuration.
Best regards,
Coleman
Hello,
I came across your post because I have the same kind of problem but for a different application.
I need to stream I2S audio data from a MCU to the ADAU1701. After some research, I got to the same conclusion, i.e. the best way to do it without a synchronous MCLK it is to configure the MCU as a slave and supply LRCLK/BCLK from the ADAU1701.
There is an interesting article on Planet Analog that deals with this matter :
http://www.planetanalog.com/document.asp?doc_id=528195&site=planetanalog
Did you make it work?
Stephane
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