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ADS1216: how do you start a conversion with this device?

Fausto Bartra1
Intellectual 435 points
Part Number: ADS1216

is there more information on this device?

my set up is as follows:

1.- 1st frame:  590047h = unipolar

2.- 2nd frame: 50000Ch = fosc/256, Vref int, Vre 2.5V, Buff off, MSB 1st

3.- 3thd frame: 510008h = channel 0, with COMM

4.- wait for DRDYn = 0

5.- 4th frame:  01h = read data  = 24 bits follow (data value appears correct)

6.- wai for DRDYn = 1

7.- then DRDYn stay high for 125ms (??)

any suggestions

Please email me more info on this part

Data sheet is not complete

Thank you

Fausto Bartra

fbartra@tekran.com

  • 0
    TI__Guru** 113765 points
    Hi Fausto,

    After making sure PDWN, DSYNC and RESET pins are pulled high and DVDD and AVDD supplies are active, make sure the POL pin is set to the correct mode for your SPI communication. Make sure you keep CS low throughout the entire communications transaction. Also make sure you have a proper oscillation on the XIN/XOUT pins ( or the proper clock frequency is provided from a clock source on XIN).

    Without writing anything to the ADS1216, read the registers and compare to the default settings in the datasheet to make sure your communication is setup properly. Also with a scope or logic analyzer verify that the DRDY pin is pulsing at the default data rate. If you do not see this pin toggling, then most likely there is a supply or other issue as mentioned in the first paragraph above.

    If things appear to be working at this point, you can try writing to the ADS1216, then verify your writes with a register read. DRDY transitioning from a high to low state signal a conversion has completed and can be read from the device.

    Pulsing DSYNC will restart a conversion otherwise if the DSYNC, RESET, and PDWN pins are high the device should be converting and DRDY toggling.

    When using the internal reference make sure that VREFOUT connects to VREF+ and VREF- connects to AGND. Also in your code comment you stated fosc/256 when the value sent is fosc/128.

    Best regards,
    Bob B
  • 0 in reply to Bob Benjamin
    Intellectual 435 points
    Thanks Bob:

    I check all you have mentioned above.
    I am getting the proper readings back from the ADC,
    but the time it takes for the next conversion is 125ms ??? (.i.e. DRDRYn pin goes low again)

    it will help a lot if you could email me more info on this device........

    otherwise, Here are some questions:
    1.-is there any documentation on how to use the DSYNC pin? (timing diagram..etc)?
    2.-Also what are the FSR registers for??
    3.-Does the DRDYn pin need a pull up?
    4.-can analog input be from 0V to 5V for VREF = 2.5V internal, AVDD =5V, DVDD=3.3V, Buffer = disable?
    5.-What is the conversion time??

    Thank you again
    Fausto Bartra
  • 0 in reply to Fausto Bartra1
    TI__Guru** 113765 points

    Hi Fausto,

    Pretty much everything you need to know is in the datasheet, but I understand that it may not be clear or easy to find.  See my responses below:

    Fausto Bartra1 said:
    Thanks Bob:

    I check all you have mentioned above.
    I am getting the proper readings back from the ADC,
    but the time it takes for the next conversion is 125ms ??? (.i.e. DRDRYn pin goes low again) [Bob] This really depends on the master clock frequency you are using and the register settings.  125ms period is 8sps data conversion rate.  The data rate (fdata) is defined and the calculation shown on the DEFINITIONS section on page 32 of the datasheet.  Basically the data rate is fmod/Decimation Ratio.  The decimation ratio is in 2 registers as an 11 bit value and the default is 0x780 (1920 decimal).  The fmod is fosc/128, so if the oscillator frequency is 2.4576MHz, the fmod frequency is 19200 and the data rate at 10sps (19200/1920).  So depending on the actual clock frequency you appear to be close to this data rate.  A 2MHz clock would be about 8sps.

    it will help a lot if you could email me more info on this device........

    otherwise, Here are some questions:
    1.-is there any documentation on how to use the DSYNC pin? (timing diagram..etc)? [Bob] DSYNC timing diagram is on page 9 of the ADS1216 datasheet and the explanation is on page 19 under DSYNC OPERATION.
    2.-Also what are the FSR registers for?? [Bob] These are the Full-Scale calibration registers used for gain correction.  You would generally not write to these register as the device will automatically write to the FSC and OCR (offset calibration) registers following a calibration command.  This information is found on page 17 in the CALIBRATION section.  The self calibration commands are SELFCAL, SELFOCAL and SELFGCAL and are listed in the COMMAND DEFINITIONS on page 26.
    3.-Does the DRDYn pin need a pull up? [Bob] No, as DRDY is an active push-pull output.
    4.-can analog input be from 0V to 5V for VREF = 2.5V internal, AVDD =5V, DVDD=3.3V, Buffer = disable? [Bob] The full-scale input range is given in the Electrical Characteristics table on page 3 for 5V AVDD.  See the discussion on Full-Scale Range on page 33 of the datasheet.  With the PGA setting at one, the FSR is 5V (or +/-2.5V), so in unipolar mode you can measure 0 to 5V from the information you provided.
    5.-What is the conversion time??[Bob] See my answer above.

    Thank you again
    Fausto Bartra

    Best regards,

    Bob B