PCM2906C: S/PDIF input from DIT4096

A small addition to the original post:

We captured the I2S data between the PCM1801 and DIT4096 using a logic analyzer. We then converted the captured I2S data back to audio and could clearly hear the original recorded audio. So we are now confident that the I2S input to the DIT4096 is valid/correct.    

Hello Jonas,

Thank you for the thorough explanation of your problem.  The PCM2906C does only accept the outputs shown below. 

I would recommend continuing down the signal chain. Using the logic analyzer, you could probe the optical tx and rx to see if the signal is making it to the PCM2906C input as expected.

Would it be possible to send a schematic? In particular, I would like to look at the connection between the DIT4096 and the optical transmitter as well as the connection between the optical receiver and the PCM2906C. 

Best,
Andrew

Hi Andrew,

Thank you for your response.

That at least explains why we could not get it to work using the 24-bit PCM1808 ADC. So let's focus on getting the PCM1801 16-bit ADC solution to work.  

The image below is a snippet of the S/PDIF signal taken using the logic analyzer. We do not see any abnormalities between the DIT4096 output and the PCM2906 input. Measuring the pulse widths at arbitrary places, it seem to be preserved at least down to 2 ns (minimum difference we could measure, limited by our logic analyzer sampling frequency). We also tried connecting the DIT4096 S/PDIF output to a Toslink speaker and were able to play/hear the sound entering the microphone (although there where quite much static/humming noise also present, not sure why). 

We could send the schematic, but would need to hide away a few non-related details first. First, can you confirm that you agree with our SW configuration of the DIT4096? Right now we do not do any changes to the channel status data buffers which we are unsure if we should. Could it be an issue related to the PRO/Consumer and copyright bits that are sent over the S/PDIF protocol?               

.

Best regards,

Jonas

Hello Jonas, 

So far the DIT4096 looks correct. I will check with the larger team about the PRO/Consumer copy bits to see if this could be the issue. However, I would like rule out a schematic issue if at all possible. 

Best,
Andrew

Hi Andrew,

Thank you for checking with the team. What would be the most convenient way to send you the schematics in private? 

Best regards,

Jonas 

Hi Jonas,

Email would be best. Can I reach out to you on the email listed for your myTI account?

Best,
Andrew

Hi Andrew,

Yes, please do that.

Regards,

Jonas

Hi Jonas,

Thank you for sharing the schematic.

Jonas Hansson said:

The PCM2906C S/PDIF input and USB connection we have verified by connecting it to another S/PDIF source and have had the audio successfully conveyed to a computer. The optical transmitter and receiver we have also managed to rule out to be the root cause.

I believe this means that you have verified performance using an external SPDIF signal with the PCM2906C (although with a 24-bit)? Have you done this test with the 16-bit format and the PCM2906C plays to the computer correctly? Essentially, I am looking to confirm that the PCM2906C/optical receiver is verified with the 16-bit format. 

If this is true then, I the disconnect would be between the DIT4096 output and the PCM2906C. Which points to a formatting miss match since it seems like the signal chain works (outputs data) from the mic input to the optical receiver (which I believe you suspected in the quote below), 

Jonas Hansson said:

Could it be an issue related to the PRO/Consumer and copyright bits that are sent over the S/PDIF protocol?               

If we can confirm that the disconnect is between these two devices, please provide a capture of the S/PDIF protocol packet from the DIT4096/transmitter and a data packed that worked on the receiver/PCM2906C. Ideally, this will show us if there is a formatting mismatch.

Best,
Andrew

Hi Andrew,

Andrew J said:

I believe this means that you have verified performance using an external SPDIF signal with the PCM2906C (although with a 24-bit)? Have you done this test with the 16-bit format and the PCM2906C plays to the computer correctly? Essentially, I am looking to confirm that the PCM2906C/optical receiver is verified with the 16-bit format. 

If this is true then, I the disconnect would be between the DIT4096 output and the PCM2906C. Which points to a formatting miss match since it seems like the signal chain works (outputs data) from the mic input to the optical receiver (which I believe you suspected in the quote below), 

The S/PDIF source in this case was the S/PDIF output of the same PCM2906C, I should have been more clear about that. Below I tried to visualize the signal path, the bold components are on the SPDIF Transmitter schematics (SPDIF_Transmitter_24bit.PDF) I sent you. The looping was done by connecting an optical fiber between U1 and U4. So the optical receiver and the PCM2906C input have been verified (at least with its own S/PDIF output as source).     

Computer -> [USB] -> PCM2906C -> [S/PDIF, 16bit, 48kHz] -> Optical transmitter -> Optical Reciever -> 

                                                                                                                                                                      |

                                                                                                                                                                      v

                                     Computer <- [USB] <- PCM2906C <- Optical Reciever  <- Optical transsmitter < -

Andrew J said:

If we can confirm that the disconnect is between these two devices, please provide a capture of the S/PDIF protocol packet from the DIT4096/transmitter and a data packed that worked on the receiver/PCM2906C. Ideally, this will show us if there is a formatting mismatch.

We got our hands on another logic analyzer that supports S/PDIF decoding. Analyzing the working S/PDIF source (the PCM2906C S/PDIF output) it has the following channel status blocks bits set to logic '1' (starting at bit index 0): Bit[9] = 1, Bit[15] = 1 and Bit[25] = 1, rest of the Bits are logic '0'. From the S/PDIF specification, the Bit[8:15] indicates the kind of equipment that generates the digital audio interface along with the generation status. Bit[24:27] indicate the sampling frequency, which in this case is 48 kHz which is correct.

Analyzing the DIT4096 S/PDIF output all the channel status block bits are logic '0', this is with the following SW configuration done to the DIT4096:

• [Register] Value
• [0x03] 0xAD
• [0x02] 0x04

We tried configuring the DIT4096 channel status data buffer (following Figure 9 in the datasheet) to match the PCM2906C output but the value we tried to program into the UA buffer we could not read back successfully. Below is a code snippet along with some comments. We will continue to investigate this further tomorrow.   

Also, in Table VIII in the DIT4096 datasheet there is a CS_N column, what does it  mean? 

DIT4096Write(0x03, 0xAD);
DIT4096Write(0x02, 0x04);
delay(100);                                 //Delay 100 ms after power up. 
uint8_t BTD = 1;                             //Set BTD to 1
DIT4096Write(0x07, BTD);                     //Write BTD to register 0x07
SerialUSB.println(DIT4096Read(0x07));        //Readback register 0x07, response is 0x01: OK!

delay(500);
SerialUSB.println(DIT4096Read(0x08),HEX);    //Read register 0x08, response: 0xFB
delay(500);
DIT4096Write(0x08, 0x00);                    //Write 0x00 to register 0x08
SerialUSB.println(DIT4096Read(0x08),HEX);    //Read register 0x08, response is 0xFB: NOT expected. 

BTD = 1;                                     //Set BTD to 0
DIT4096Write(0x07, BTD);                     //Write BTD to register 0x07

Best regards,

Jonas     

Hello Jonas, 

Thanks for the added information. 

Let me check with the team on the proper use of the CS_N header. From what I can tell this is related to "FIGURE 6. Write Operation Format" and may be the header byte need to write to that register, but I will need to look into this further. 

Best,
Andrew

Hi Jonas, 

Quick update (I am still reviewing all the info with the team). The DIT4096 tends to be hard to program.  Please try the following config script for the DIT4096 and let me know if this is configuring the device. 

# PCM9211_Init.txt
#this script is for SPDIF-->RXIN0-->DIR-->MainOutput, Record sound from SPDIF to PC through TAS1020

#1, Chose RXIN0 to DIR
#2, Active DIR
#3, chose DIR output as Mainoutput's source.

#Also HW modification
#1, Flying to High Level(3.3V) to make sure U7's output is Hi-Z
#or 2, TAS1020 output logic high on P1.2 I2S enable signal. 
#**************************************

#System RST Control
#w 80 40 00
w 80 40 33
w 80 40 C0

#XTI Source, Clock (SCK/BCK/LRCK) Frequency Setting
# XTI CLK source 12.288 and BCK 3.072, LRCK 48k = XTI/512
w 80 31 1A
w 80 33 22
w 80 20 00
w 80 24 00
#ADC clock source is chosen by REG42
w 80 26 81

#XTI Source, Secondary Bit/LR Clock (SBCK/SLRCK) Frequency Setting
w 80 33 22

#*********************************************************
#-------------------------------Start DIR settings---------------------------------------
#REG. 21h, DIR Receivable Incoming Biphase's Sampling Frequency Range Setting
w 80 21 00

#REG. 22h, DIR CLKSTP and VOUT delay
w 80 22 01

#REG. 23h, DIR OCS start up wait time and Process for Parity Error Detection and ERROR Release Wait Time Setting
w 80 23 04

# REG 27h DIR Acceptable fs Range Setting & Mask
w 80 27 00

# REG 2Fh, DIR Output Data Format, 24bit I2S mode
w 80 2F 04

# REG. 30h, DIR Recovered System Clock (SCK) Ratio Setting
w 80 30 02

#REG. 32h, DIR Source, Secondary Bit/LR Clock (SBCK/SLRCK) Frequency Setting
w 80 32 22

#REG 34h DIR Input Biphase Signal Source Select and RXIN01 Coaxial Amplifier
#--PWR down amplifier, Select RXIN2
#w 80 34 C2
#--PWR up amplifier, select RXIN0
w 80 34 00
#--PWR up amplifier, select RXIN1
#w 80 34 01

#REG. 37h, Port Sampling Frequency Calculator Measurement Target Setting, Cal and DIR Fs
w 80 37 00
#REG 38h rd DIR Fs
r 80 38 01
#***********************************************************
#------------------------------------ End DIR settings------------------------------------------


#***********************************************************
#---------------------------------Start  MainOutput Settings--------------------------------------
#MainOutput
#REG. 6Ah, Main Output & AUXOUT Port Control
w 80 6A 00

#REG. 6Bh, Main Output Port (SCKO/BCK/LRCK/DOUT) Source Setting
w 80 6B 11

#REG. 6Dh, MPIO_B & Main Output Port Hi-Z Control
w 80 6D 00
#***********************************************************
#------------------------------------ End MainOutput settings------------------------------------------

# read back all registers to ensure GUI integrity
r 80 20 5E

Best,
Andrew

Hi Andrew,

Looking at the script in your post it does not seem compatible with the DIT4096(?). 

Best regards,

Jonas

Hello Jonas, 

Sorry for the confusion.

PCM9211 is a similar device. You can use the structure; however, the registers might be different. Attached is another script which should be compatible, but the first script is good to show the steps for DIR and DIT programming.

DIX4192_5F00_script.txt

Best,
Andrew

Have you found anything that will result in the PCM2906C recording a S/PDIF signal that has been applied to the PCM2906C DIN pin?

Hello Michael Sirkis, 

I believe this question is related to (+) PCM2906CEVM-U: S/PDIF input doesn’t work. - Audio forum - Audio - TI E2E support forums. I have replied to you in your original thread. 

Best,
Andrew