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Original question:

ADS1278: Reading data in SPI fixed mode

ADS1278: DRDY pin holds up during TDM fixed mode

minju kim
Prodigy 30 points
Part Number: ADS1278

Dear

I attached ADS1278 schematic, and expecting pin29(DRDY) goes down periodically but it holds up
high all the time.
1. Do I have to input SCLK clock signal from a microcontroller to see the DRDY goes down?
2. I have not connected any AINN, AINP pins to anything. Does this affecting DRDY's output?

--configuration
MODE[1:0] : 11 low speed
FORMAT[2:0]: 001 TDM fixed
CLKDIV: 0 low speed

  • 0
    TI__Guru 63855 points

    Hello,

    It looks like you're in SPI/TDM/Fixed format of operation which it sounds like is desired.  If you're looking for a quick check on functionality then we'll recommend terminating some more of the currently floating inputs.  Connect the analog inputs to GND, /SYNC to +3.3V, and SCLK to GND.

    Also, since it's not shown, make sure you have proper decoupling on all power-supply pins as shown in the EVM User's Guide.  

    If those things don't seem to change the results, try pulsing the /SYNC pin to see if it has any effect on DRDY.

  • 0 in reply to Collin Wells
    Prodigy 30 points

    Dear

    Thank you for your response. I have some questions:

    1.Connect the analog inputs to GND, /SYNC to +3.3V, and SCLK to GND.  <---- for SPI/TDM/Fixed

    format of operation should I always pull up SYNC pin to 3.3V?

    2."Connect the analog inputs to GND, /SYNC to +3.3V, and SCLK to GND." even after following 

    this direction the DRDY pin stays high. So as you mentioned I start to pulsing SYNC pin and

    short duty pulses comes out of the DRDY pin. Does this mean that I need to initially input a few pulse into the SYNC pin for SPI/TDM/Fixed format of operation?

  • 0 in reply to minju kim
    TI__Guru 63855 points

    Hello,

    1.)  Many applications use the /SYNC pin to trigger the beginning of conversions with an external event.  You had it floating, which is undesirable for a digital input so we requested that it be connected to a known potential (in this case +3.3V).  Recommended that you connect it to a GPIO on your MCU so you can use the /SYNC function.

    2.)  Thank you for the updates.  Pulsing /SYNC should not be required to start operation, however with SCLK tied low as we requested, the device is pulsing /DRDY which indicates it is waiting for you to read data as described in Figure 76. Try finishing the connections to the device and then try to read data.

  • 0 in reply to Collin Wells
    Prodigy 30 points

    Thank you so much for your time and help.