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Original question:

ADS124S08: Regulator Choice for ADS124S08

ADS124S08EVM: ADS124S08EVM

Wael Hazin
Prodigy 195 points
Part Number: ADS124S08EVM
Other Parts Discussed in Thread: ADS124S08

Hello Bob:

 

I hope all is well with you. I have been using the Eval board to test out some of our new sensor designs and are happy with its performance. During the last few days, I have been working on having the ADC on the eval board communicate with our Nordic MCU via the SPI bus on J3. However, I have not been able to read any register value from the ADC although I am using Mode 1, and shorted JP1 to hold the onboard MCU in reset. I also can see on the scope the clk and MOSI signal but I receive nothing on the MISO signal. Also the CS functions as it should where it goes low during a read or write. I have tried 1, 4, and 8 MHz bus speeds. I am trying to just read the status register. I have run out of things to check and your time and effort will be greatly appreciated in helping me get to the bottom of this issue. Am I missing something? Please feel free to call me if possible as I am running out of time to get this issue resolved.

 

561-350-6939

Regards,

  • 0
    TI__Guru** 112895 points

    Hi Wael,

    I've got a pretty hectic schedule today, but I think your problem may be related to the RESET.  This pin must be pulled high on J3 as it is normally driven by the micro through the level-shifters and the level-shifters are disabled when JP1 is pulled low.

    Also, the ADS124S08 will be held in a reset state if not all of the supplies are active.  You must make sure DVDD, IOVDD and AVDD are at nominal operating voltage or you will not be able to communicate with the device.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 195 points

    Hi Bob,

    it was the Reset on J3. Thank you!!

  • 0 in reply to Wael Hazin
    Prodigy 195 points

    Hi Bob:

    I have another issue that may seem simplistic, is there anyway to command the ADC to digitize all channels without having to configure each channel individually in the INPMUX register? we are using all 12 channels as 6 differential pairs. I would also like to read all channel conversion data at once if possible to keep the mcu in sleep mode. again, your time and effort will be greatly appreciated.

    Regards,

  • 0 in reply to Wael Hazin
    Prodigy 195 points

    Anyone please???

  • 0 in reply to Wael Hazin
    TI__Guru** 112895 points

    Hi Wael,

    I apologize that I missed responding to your previous question.  Actually, the information is given in the ADS124S08 datasheet.  The ADS124S08 only has a single ADC with an input mux.  This means that you can only take one measurement per input pair combination  at a time with this device.  In other words, you set the mux and take a measurement and repeat the process for each input pair combination.

    Again, I apologize for the delayed response.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 195 points

    Hi Bob:

    Thanks for the reply! I knew it was a single ADC but I was hoping there would be a way to "scan" all channels without having to configure the mux. what would be the fastest way to scan all differential channels? what I'm trying to do is minimize the amount of time the mcu is talking to the ADC. I can think of 2 ways to do this. One, send the start command and wait for the conversion. Two, send the start command and sleep while waiting for the Data Ready. I guess what I trying to ask is at what point can I send the start command for the 2nd channel while I'm reading the first conversion data without corrupting it to minimize the down time of the ADC and increase the down time of the mcu? I plan on using the single-shot mode as I need to have all channels digitized within 10 to 13 ms. I hope you understand what I'm trying to do. Let me know if you need any further clarifications. 

    Regards,

  • 0 in reply to Wael Hazin
    TI__Guru** 112895 points

    Hi Wael,

    This is the way I would do it.  Use DRDY as an interrupt to the micro to wake it up read the last conversion result.  As the SPI is full-duplex, you can issue the WREG command at the same time as you read the conversion data.  This process is shown in Figure 92 of the ADS124S08 datasheet on page 71 and discussed in section 9.5.4.3.  The only addition to this sequence is the START command which can be sent immediately after the WREG sequence.  If only the mux is changed you would only need the first part of the sequence shown in Figure 92 as this sequence is actually showing a write to 2 registers.

    Best regards,

    Bob B