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Data not read from Multiple AD7190 IC's

Hello Everyone,

       MSP432P401M controller is interfaced with 8 AD7190 Ic's through SPI communication. I am using 3 wire SPI  interface. When I try to communicate with single AD7190 IC's I can successfully read load cell/ strain gauge data. But, when I trying to communicate data from 1,2 and 3rd IC simultaneously then 3rd IC is not selected..Instead of 3rd the data read from 2nd iC so if load cell data will change then same value will change for 2nd and 3rd IC.

the sequence is :-

-CS low

-Delay in us

-write in communication register for channel selection 1

-wait for RDY pin low

-read data

-write in communication register for channel selection 2

-wait for RDY pin low

-read data

-Delay in us

-CS high.

-same sequence to read data from 2nd,3rd IC..

Please suggest.

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  • okay.So what is the pull up resistor value?? I have attached schematic.

  • Hi,

    Schematic looks fine. You could use pull-up resistors on CS lines and SPI lines anywhere varying from 100k to 1Meg resistors. SYNC pins have internal pull-ups, so there is no need of external pull-up as used in the design.

    You could also club the SYNC lines if the microcontroller can drive 8 inputs. 

    Thanks 
    Vikas J

  • Hello,

      As I tried with pull up register but still I can't read from 8 different IC's. I have few basic questions :-

    1) Is issue regarding clock freq??I am working on 3Mhz clock cycle with 50Hz data rate. What is the range of SCLK freq ?

    2) I am trying to read data from single AD7190 Ic. clock is 3Mhz. default register read successfully but I am unable to read strain gauge data on channel 1 and 2. 

    3) sometimes DRDY pin is not low while read data.what is the reason??

  • Hi,

    1. 3MHz SCLK should not be a problem. The device works upto 5MHz.
    2. Have you enabled channel 1 and 2? Is the SPI write working? 
    3. There are multiple scenarios where RDY goes high.
      1. If SYNC is low, DRDY pin is pulled high.
      2. If the data is being updated, DRDY goes high.
      3. If calibration is enabled, DRDY goes high.

    Please go through the datasheet DIGITAL INTERFACE section on page 29 for more info.

    Thanks

    Vikas J