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ADS8691: Problem configuring ADS8691

user1219445
Prodigy 140 points

Part Number: ADS8691

Hi

I'm having trouble configuring the ADS8691 for 0-5.12V input range. I can correctly readout the ADC value, but it stays in -12V - +12V range, whatever I do.

Here are some scope shots of the configuring (sorry, I could not attach all 4 probes because the testpoints were forgotten) :

yellow: CS/Convst, magenta: SCLK

yellow: SCLK, magenta: SDI

yellow: SCLK, magenta: SDO

Can you help me on what I'm doing wrong?

Kind regards

Claudio

  • 0
    TI__Mastermind 25070 points

    Hello Claudio,

    Try programing the registers, then read the registers you programmed, this will help to see if and where the issue is.  Table 3 of the datasheet will help with the range selection, also page 41 helps explain how to write to registers. Are you programming any other registers, do those work correctly?

    I would also suggest using a known DC input voltage to check the ADCs results

    -Cynthia

  • 0 in reply to Cynthia
    Prodigy 140 points
    Hi Cynthia

    Funny enough this solves the problem. Writing alone did not work. But now when I read it after writing it works.
    Thanks for the hint.

    Claudio
  • 0 in reply to user1219445
    Prodigy 20 points

    Hello,I'm very happy for you.I have been trying to communicate with ADS8691,but failled to read the register.Can you show me the demo code.Thanks firstly.The following is the codes.

    // Transmit data
    GpioDataRegs.GPBDAT.bit.GPIO57 = 0;
    ////////////////write register//////////
    spi_xmit(0xD014);
    // Wait until data is received
    //while(SpiaRegs.SPIFFRX.bit.RXFFST !=1) { }
    // Check against sent data
    //rdata = SpiaRegs.SPIRXBUF;
    delay_loop();
    spi_xmit(0x000B);
    GpioDataRegs.GPBDAT.bit.GPIO57 = 1;
    // Wait until data is received
    //////////////read register///////////
    GpioDataRegs.GPBDAT.bit.GPIO57 = 0;
    spi_xmit(0x4814);
    delay_loop();
    spi_xmit(0x0000);
    //while(SpiaRegs.SPIFFRX.bit.RXFFST !=4) { }
    delay_loop();
    result = SpiaRegs.SPIRXBUF;
    // if(rdata != sdata) error();
    GpioDataRegs.GPBDAT.bit.GPIO57 = 1;
    //delay_loop();

  • 0 in reply to Cynthia
    Prodigy 20 points
    hello,I have the problem.Firstly,I can read the data in default condition .Then I tried to write the gegister,but failed.The following is the code.Can you give me some advises?
    ////////////////write register//////////
    GpioDataRegs.GPBDAT.bit.GPIO57 = 0; //pull down CS
    spi_xmit(0xD014); //write register
    delay_loop();
    spi_xmit(0x000B); //set range 1.25*verf
    delay_loop();
    GpioDataRegs.GPBDAT.bit.GPIO57 = 1; //pull up CS
    //////////////read register///////////
    GpioDataRegs.GPBDAT.bit.GPIO57 = 0;
    spi_xmit(0xC810);
    delay_loop();
    spi_xmit(0x0000);
    rdata = SpiaRegs.SPIRXBUF;
    GpioDataRegs.GPBDAT.bit.GPIO57 = 1;
    delay_loop();
  • 0 in reply to Jun Sun
    TI__Mastermind 25070 points
    Hello Jun Sun,
    Unfortnetly TI does not have sample code. If you are having issues, please create a post and we will try to address the problem
    Regards
    Cynthia