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question about ADS1271 with MCU with SPI 16bits buffer

Miguel Amezcua Peregrina
Genius 4015 points
Other Parts Discussed in Thread: ADS1271

Hii

Hope you're doing great

I have a question... My MCUs SPI is 16 bit max. but the data from the ADS is 24 bits long. I was wondering if I could do 2 transactions of 12 of three of 8 and if possible, how could I do it...

best regards 

  • 0
    TI__Guru 66256 points

    Hola Miguel,

    Are you using the ADS1271 in SPI Mode or Frame-Sync Mode? In SPI Mode, you may send SCLKs in bursts of 8 or 12 pulses in order to read all 24 bits of data. The only concern is to make sure that the total time to read the data (24 SCLKs + additional delays) is less than the data rate period (1/fDATA).

    However, in Frame-Sync Mode, the ADS1271 expects a free-running, continuous SCLK, so I would not recommend sending SCLKs in multiple bursts in this case.

    Saludos,

  • 0 in reply to Ryan Andrews
    Genius 4015 points

    Hi Rayan

    Yees im using it on SPI mode.

    I was checking and i need to do 2  transmissions but between transmissions i need to copy tge data from the buffer to an arranent.... Thanks for tge answer!!

  • 0 in reply to Ryan Andrews
    Genius 4015 points

    Hi Rayan

    Hope you're doing great.

    This is the schematic Im using on the board with the ADC. For some reason I still don't undertand, the DRDY pin is in low with some noise and its supposed to be in high no? IS there any problem with this configuration??

    I tried to use it connecting the MCU PWM on the input in order to make some test but the interrupt to the MCU is not happening because the pin DRDY is on low and well... I don't know what could be wrong...

    Thanks!!

  • 0 in reply to Ryan Andrews
    Genius 4015 points

    Hi Rayan

    I was doing some meassures and this is what I saw on TP12 (the MODE pin)

    is that normal? the pin is not connected to anything, since the Datasheet said "float" we assume that that was correct...

    And the TP8 (DRDY pin) this is what I have

    so... I don't know why Im having this if the format is already selected and everything... whats going on?

  • 0 in reply to Miguel Amezcua Peregrina
    TI__Guru 66256 points

    Hi Miguel,

    In the schematic, you show a 27MHz clock, so the expected data rate is 52.7kSPS. The /DRDY pulses that you show above appear to occur at the correct interval (1/52.7k = ~19us). The reason that /DRDY is idling low between conversions is that you are not reading the data and therefore, you are not sending SCLKs. This behavior is described in Figure 63 on page 25 of the ADS1271 datasheet.

    Regarding the waveform that you see on the MODE pin, it's difficult to say for sure where this is coming from. It may be coupling from elsewhere on your board, or perhaps this is due to some RC network connected internally to the pin that is charging/discharging. Whatever the case may be, you have configured the device correctly for High-Resolution Mode. As long as you are getting consistent /DRDY pulses, then the modulator and digital filter should be operating without interruption.

    Please let me know if you have any additional questions.

    Saludos,

  • 0 in reply to Ryan Andrews
    Genius 4015 points

    Hola Ryan

    Ryan Andrews said:
    In the schematic, you show a 27MHz clock, so the expected data rate is 52.7kSPS.

     

    yep. that correct. 

    Ryan Andrews said:
    The /DRDY pulses that you show above appear to occur at the correct interval (1/52.7k = ~19us). The reason that /DRDY is idling low between conversions is that you are not reading the data and therefore, you are not sending SCLKs. This behavior is described in Figure 63 on page 25 of the ADS1271 datasheet.

    ooooh now I get that image hehe so the DRDY is working properly

    Ryan Andrews said:
    Regarding the waveform that you see on the MODE pin, it's difficult to say for sure where this is coming from. It may be coupling from elsewhere on your board, or perhaps this is due to some RC network connected internally to the pin that is charging/discharging. Whatever the case may be, you have configured the device correctly for High-Resolution Mode. As long as you are getting consistent /DRDY pulses, then the modulator and digital filter should be operating without interruption.

    According to an answer you gave in this post and also the datasheet: 

    Wouldnt I have problems with the setting time of the ADS with the changes of MODE pin? 

    Muchas gracias Ryan!!

  • 0 in reply to Ryan Andrews
    Genius 4015 points
    Im having a problem... the code is not reaching the interrupt because the DRDY pin is not requesting it...
  • 0 in reply to Miguel Amezcua Peregrina
    Genius 4015 points
    I tried something. Writing a code with just spi and it worked but why when trying to use the interrupt it didn't work?
  • 0 in reply to Ryan Andrews
    Genius 4015 points
    ok. I already figured out what was going on. the problem is that the MCU drops the voltage. Everything is ok before the resistor. After the resistor, the voltage drops. you have any idea?