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ADS1118 when to read?

dan kantorski
Intellectual 910 points
Other Parts Discussed in Thread: ADS1118

I have reviewed the data sheet and forums but still  have a question regarding reading the conversion.  I will be using the device in the one shot mode.  it says "The conversion data are read by writing a '1' to the OS bit, followed by shifting the conversion data out."  Is it that you initiate the conversion, poll the Drdy or CNV_RDY_FL bit for a low and then you can start downloading the conversion data and register?  If the chip goes into power down can you clock out your data?  Also, is the CNV_RDY_FL a read only register, and starting a conversion I assume automatically sets Drdy high and the CNV_RDY_FL high?

  • 0
    TI__Guru 55466 points

    Hi Dan,

    If the device will be used in single shot mode, the user will trigger the conversion writting '1' to the OS bit.  After triggering the conversion on the first transaction, the user may poll DOUT/DRY pin to verify if the conversion data is ready.  When CS is set low, without sending any clocks, you may monitor DOUT/DRDY to see if the conversion is still in progress.  If DOUT/DRDY asserts low, the conversion is complete and you may read the conversion data.  You may still read the conversion data if the device goes into power down mode.  The Config register read value of Bit[0] is always one; this is not documented clearly on the datasheet; therefore the user needs to poll the DOUT/DRDY.

    Every communication transaction is 4 bytes long, the first 2 bytes that are read is the previous conversion data and the second 2 bytes that are read are the current CONFIG register data.  On every 4 byte transaction, after writing the new CONFIG on the first two bytes, you should be able to read the newly updated CONFIG data on the second two bytes.   

    Thank you and Best Regards,

    Luis

  • 0 in reply to Luis Chioye
    Prodigy 10 points

    Hi Luis,

    then the datasheet is a bit misleading - Page 19, "Operating modes" states, that I should monitor the OS bit - as it will go 0 on conversion start, and then go back to 1 when the single-shot is completed.

    It is also interesting, that if - in single shot mode - I continuously poll the chip, I will be able to detect the 'end of conversion' bit going to 0. If I decide to do something else and leave the chip running - the bit will be always 1.

    When do you think the document will be corrected?

    M.W.

  • 0 in reply to Marcin Wolcendorf
    TI__Guru 55466 points

    Hi Marcin,

    The datasheet was updated recently addressing the documentation issue above.  Please find the latest datasheet below.

    http://www.ti.com/lit/ds/symlink/ads1118.pdf

    The user can always monitor the DOUT/DRDY pin in single shot mode or continuous conversion mode. The DOUT/DRDY pin transitions low when data is ready for retrieval and this signal can be used to trigger the microcontroller to start reading the data. When CS is set low, without sending any clocks, you may monitor DOUT/DRDY to see if the conversion is still in progress.  If DOUT/DRDY asserts low, the conversion is complete and you may read the conversion data.  Page 20 of the updated datasheet describes this function.  

    Best Regards,

    Luis 

  • 0 in reply to Luis Chioye
    Intellectual 340 points

     

    Dear  TI  product support  .

     

    Please give yor kindly support  about  our customer's inquiry .

    Our Cutomer would like to have advice from TI    about their product design  with ADS1118.

     

    Cutomer's  old model was designed  with using 15bit(OS) refer to description in data sheet rev.b (SBAS457B) . It designed  in 2012 Jan.

    According to new rev.c（SBAS457C） data sheet,It shows difference below .

     

    ------------------------

    ◇It was  changed from rev.b to rev.c about description of Table 6. Config Register (Read/Write) P.21】.

    i).rev.b  SBAS457B config register 15bit(OS) →　rev.c 15bit(SS) .

    ii).rev.b  SBAS457B bit0(CNV_RDY_FL)  can use status conversion status  → Not used , always 1

    iii).rev.b　SBAS457B bit3(PULL_UP_EN)  bit0 default  →  rev.c 1 default

    . ------------------------

     

    Our cutomer inquiry .

     

    a)Is their any product change notice  customer should know  about  the data sheet revison change from rev.b（SBAS457B) to rev.c（SBAS457C).

    b)Customer should design with rev.c（SBAS457C)  data sheet  in  their new  product design activity ? 

    c)Please give some general advice or application note about design change  from rev.b（SBAS457B) to rev.c（SBAS457C = latest version data sheet).

       Is their any critical  point of design consideration  about that ?

     

    Thank you and  best regards.

    miyazaki