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ADS8685: SPI programming

Ricardo Sis Moreira
Prodigy 45 points

Part Number: ADS8685

Support Path: /Product/Development and troubleshooting/Help with board layout or design considerations/

Please I need help understanding the SPI programming protocol of this chip. I want to read and configure registers and read the ADC output data. As the datasheet IS NOT AT ALL EASY TO UNDERSTAND, I need clear examples that show me how to read any Register, write any Register and read the ADC data.

Consider for example my case:

1- I need to know exactly what are the 32 bits that I need to send to READ the RANGE_SEL_REG.

2- I need to know exactly what are the 32 bits that I need to WRITE the RANGE_SEL_REG in order to select de range: +-3 x Vref and Internal Reference.

3- If I use the default protocol as it comes (SPI-00-S), how do I retrieve the ADC data from the chip and how it will be formed (16bits, 32 bits, etc). Do I need to send any Command in order to Read the ADC output data?

4- If I configure the range to +-3 x Vref and Internal Reference, whats the equation to convert the the UNSIGNED INT data to float?

5- Do I have to send all data MSB first? All the data from the chip comes MSB First?

This is my schematic:

  • 0
    TI__Mastermind 25070 points

    Hello Ricardo,

    We try for our datasheets to cover all aspects that a user may need to use the device effectively, perhaps I can help to get you communicating with the device.

    On page 41 of the datasheet there is an example of the typical data transfer frame. It requires 32 SCLK, if there is less, there will be no operation, and if longer be sure that the last 32 bits to the device is the desired command.

    It is MBS first to LSB, Figure 3 and 4 can help, or the timing diagrams on page 44 (shown below) which can also help with reading data from the device

    Regards, Cynthia