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ADS1298R: DRDY signal ceases to generate

Prodigy 40 points

Replies: 6

Views: 107

Part Number: ADS1298R


I am having problem getting data out of my ADS1298, after configuring it in RDATAC mode. All my SPI routines are verified for reading and writing registers.

I have carried out many conditions to single out the problem.

- When I activate start pin and send the START command but dont read data from the device, DRDY signal is generated.. no problems. But as soon as i start reading from it, DRDY stops generating, pulls up to HIGH (5V) state.

- I have even tried to run it in RDATA (single shot) mode inside infinite loop, but I get the same result. DRDY doesnt generate! please help..

  • Hi Ninad,

    Welcome to our e2e forum! As noted in the original post on the ADS1298, are you reading out the data between DRDY pulses, ensuring that your SCLK is fast enough to retrieve all of the conversion results? The DRDY output will go high with the first SCLK after you start reading the conversion results. It should return low once the next conversion sample set or ready to be retrieved. Can you provide register details and post a scope or logic analyzer screen shot showing your communication sequence and perhaps a schematic showing your ADS1298 connections?




  • In reply to Tom Hendrick:

    ADS1298-breakout.schHere I have attached the schematic file of the board.

    I have ensured that my SCLK is fast enough to not mess up the DRDY timing, DRDY is 500SPS and SCLK is fast enough to comfortably read 27 bytes of data from the ADS.

    Register initializations:

    ADS_WREG(ADS1298_CONFIG1_REG, 0x06);		//Data Rate = Fmod/1024, Low Power Mode
    ADS_WREG(ADS1298_CONFIG2_REG, 0x10);		//Test signals are generated internally
    ADS_WREG(ADS1298_CONFIG3_REG, 0xD4);		//PD_REFBUF enable, VREFP is set to 2.4V, RLD_REF is set, RLD_REF is fed externally, RLD_BUF enabled, RLD_sense is off, RLD is connected
    ADS_WREG(ADS1298_LOFF_REG, 0x02);		//Do not use
    ADS_WREG(ADS1298_CH1SET_REG, 0x50);		//Gain = 8, Normal electrode input
    ADS_WREG(ADS1298_CH2SET_REG, 0x50);
    ADS_WREG(ADS1298_CH3SET_REG, 0x50);
    ADS_WREG(ADS1298_CH4SET_REG, 0x50);
    ADS_WREG(ADS1298_CH5SET_REG, 0x55);		//Gain = 8, Test signals
    ADS_WREG(ADS1298_CH6SET_REG, 0x55);
    ADS_WREG(ADS1298_CH7SET_REG, 0x65);		//Gain = 12, Test signals
    ADS_WREG(ADS1298_CH8SET_REG, 0x65);
    ADS_WREG(ADS1298_RLDSENSP_REG, 0x00);	
    ADS_WREG(ADS1298_PACE_REG, 0X00);
    ADS_WREG(ADS1298_RESP_REG, 0XF0);		// Respiration phase = 90, Internal Respiration of with user generated signals
    ADS_WREG(ADS1298_CONFIG4_REG, 0X00);		//64 kHz modulation clock
    ADS_WREG(ADS1298_WCT1_REG, 0x00);
    ADS_WREG(ADS1298_WCT2_REG, 0x00);

    I am sorry, I dont have any images of waveforms!

    One more detail that i think may be of interest is that - When i initialize the ADS, VCAP1 capacitor charges to about 1.019V no matter how much delay I set in the code. Only when I start reading and DRDY halts, VCAP1 voltage exceeds 1.1V (as i observed in the datasheet). Can this be the issue?

  • In reply to NINAD GANDHI:

    Hi Ninad,

    I've found a few other posts with a similar issues and typically it is caused by a pin reservation on the MCU side which prevents the pin from returning low.

    If that isn't then issue:

    What value does VCAP1 reach when exceeding 1.1V?

    You schematic is blank when I try to open it (perhaps it is trying to reference a location on your hard drive). Try posting a PDF or JPG.

    Best regards,

    Alex Smith
    Applications Engineer | Precision Delta-Sigma Converters

    Check out our helpful resources:
    TI Precision Data Converters | TI Precision Labs - ADCs | Analog Engineer's Calculator Data Converters Learning Center | Selection Guide

  • In reply to Alexander Smith:


    Sorry about the schematic. I have uploaded the schematic pdf file!

    More development on my problem is that when I changed some capacitors (prescribed in the datasheet) DRDY pin does toggle, data does come. But the problem still intermittently persists.

    So i am guessing that it is a problem with the interfacing Capacitors and Resistors. can you please point out if there are some Caps (or Res) whose prescribed values have to be stringently be followed?

    Answering your question, the voltage at VCAP1 pin reaches about 1.161V

    Please inform me if the pdf file still doesnt open, and i am attaching the schematic again.7142.ADS1298-breakout.sch

  • In reply to Alexander Smith:

    Oh yeah, and the two links don't seem to be the issue in my case!
    The MCU side seems to be okay in terms of sending signals and processing data.
  • In reply to NINAD GANDHI:

    Glad to hear that you're making progress!

    Which caps did you change?

    VCAP1 should be 22uF, not 1uF as per the Pin Function section of the datasheet.

    Any patterns that suggest a root cause of the intermittent data stream?

    Are your digital traces from the device to the MCU a reasonable length?

    Best regards,

    Alex Smith
    Applications Engineer | Precision Delta-Sigma Converters

    Check out our helpful resources:
    TI Precision Data Converters | TI Precision Labs - ADCs | Analog Engineer's Calculator Data Converters Learning Center | Selection Guide