AD7771 and DOUTx interface

Question

Hi, 
 I want to read ADC data from AD7771 via DOUT0 line - all 8 channels in 1 line. 
 
 What I did: 
 I am in SPI control mode: 
 - Set PowerMode to LP 
 - Set decimation rate (I want ODR = 1 kHz) => 1024/1 = 1024 = 0x400 - to the rigister SRC_N_MSB I wrote 0x04 and to SRC_N_LSB I wrote 0, then I update it via register 0x64 (SRC_UPDATE) 
 - Set Output format and DCLK via reg. 0x14 (DOUT_FORMAT) => DOUT_FORMAT = 0b11100100 (1 DOUTx line,CRC header,reserved,MCLK/4,Reserved). 
 - Set reference to internal via reg. 0x15 (ADC_MUX_CONFIG) => ADC_MUX_CONFIG = 0b01000000 
 
 After that I can see: 
 - DRDY pin has period of 1 khz - perfect! 
 - On the scope I can see 8x32 bits packets - looks OK to me. 
 
 Questions: 
 - Is OK when after all 8x32 bits packet the CLK still generates cloks even if the data are already sent? 
 image here: 
 
 - Where does the data start (CRC header for channel 0)?:

Finally I tried to read this data by STM32 via SAI interface, but I am not succesful. The discussion is here without answer: RE: Any advice on reading the AD7779 DOUT0 using an STM32 SAI input? 
 
 Thank you for any advice. 
 Jan.

witc · Accepted Answer

Finally! 
 This variant works to me - reading 8 channels in 1 DOUt line: 
 hsai_BlockB3.Instance = SAI3_Block_B;
 hsai_BlockB3.Init.Protocol = SAI_FREE_PROTOCOL;
 hsai_BlockB3.Init.AudioMode = SAI_MODESLAVE_RX;
 hsai_BlockB3.Init.DataSize = SAI_DATASIZE_32;
 hsai_BlockB3.Init.FirstBit = SAI_FIRSTBIT_MSB;
 hsai_BlockB3.Init.ClockStrobing = SAI_CLOCKSTROBING_FALLINGEDGE;
 hsai_BlockB3.Init.Synchro = SAI_ASYNCHRONOUS;
 hsai_BlockB3.Init.OutputDrive = SAI_OUTPUTDRIVE_DISABLE;
 hsai_BlockB3.Init.FIFOThreshold = SAI_FIFOTHRESHOLD_EMPTY;
 hsai_BlockB3.Init.SynchroExt = SAI_SYNCEXT_DISABLE;
 hsai_BlockB3.Init.MonoStereoMode = SAI_STEREOMODE;
 hsai_BlockB3.Init.CompandingMode = SAI_NOCOMPANDING;
 hsai_BlockB3.Init.TriState = SAI_OUTPUT_NOTRELEASED;
 hsai_BlockB3.Init.PdmInit.Activation = DISABLE;
 hsai_BlockB3.Init.PdmInit.MicPairsNbr = 1;
 hsai_BlockB3.Init.PdmInit.ClockEnable = SAI_PDM_CLOCK1_ENABLE;
 hsai_BlockB3.FrameInit.FrameLength = 256;
 hsai_BlockB3.FrameInit.ActiveFrameLength = 1;
 hsai_BlockB3.FrameInit.FSDefinition = SAI_FS_STARTFRAME;
 hsai_BlockB3.FrameInit.FSPolarity = SAI_FS_ACTIVE_LOW;
 hsai_BlockB3.FrameInit.FSOffset = SAI_FS_FIRSTBIT;
 hsai_BlockB3.SlotInit.FirstBitOffset = 0;
 hsai_BlockB3.SlotInit.SlotSize = SAI_SLOTSIZE_32B;
 hsai_BlockB3.SlotInit.SlotNumber = 8;
 hsai_BlockB3.SlotInit.SlotActive = SAI_SLOTACTIVE_0|SAI_SLOTACTIVE_1|SAI_SLOTACTIVE_2|SAI_SLOTACTIVE_3
 |SAI_SLOTACTIVE_4|SAI_SLOTACTIVE_5|SAI_SLOTACTIVE_6|SAI_SLOTACTIVE_7; 
 
 Thank you all!

jananisunil · Answer

Hi witc , 
 Regarding the data read using SAI- Attached below are the settings with which I was able to get the data read successfully 
 Init:

Details:{AudioMode = 3, Synchro = 0, SynchroExt = 0, MckOutput = 0, OutputDrive = 0, NoDivider = 0, FIFOThreshold = 0, AudioFrequency = 0, Mckdiv = 0, MckOverSampling = 0, MonoStereoMode = 0, CompandingMode = 0, TriState = 0, PdmInit = {Activation = DISABLE, MicPairsNbr = 0, ClockEnable = 0}, Protocol = 0, DataSize = 64, FirstBit = 0, ClockStrobing = 1}

FrameInit 
 Details:{FrameLength = 256, ActiveFrameLength = 1, FSDefinition = 0, FSPolarity = 0, FSOffset = 0}

SlotInit: 
 Details:{FirstBitOffset = 0, SlotSize = 0, SlotNumber = 32} 
 
 Here it has been configured in such a way that SAI reads 32 slots, where: 
 channel0 = (data[1] << 16 ) | (data[2] << 8) | (data[3]) 
 channel1 = (data[5] << 16 ) | (data[6] << 8) | (data[7]) 
 and so on.

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AD7771 and DOUTx interface

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