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ADC 7708 occasionally gives "0" in data register when in continuous conversion mode

Category: Hardware
Product Number: AD7708

We use AD7708 in continuous conversion mode. The software is communication in following steps during every read after initialization.  

1. Select channel

2. Wait for 1 ms 

3. Read status register every 1 msec 

4. When RDY bit is set read data register   

Typically, after selecting the channel, it takes > 10msec to see the RDY bit set in status register which is expected.. 

However occasionally we see the status register returning RDY bit set immediately after channel select is sent. and in this case the data register will read as '0' 

Once this scenario occurs it starts getting into above erroneous situation more often but not all the time.     

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  • Hi, 

    Would you be able to share your register map settings please? If you can try to readback all of the register settings just to confirm that everything is configured properly then that would be great. 

    And can you also send a scope shot of your /RDY pin? For example, at continuous conversion mode, just stop reading the conversion and you just probe and monitor the /RDY pin to see if this pin is pulsing at expected output data rate?

    Thanks,

    Jellenie

  • Thank you for responding. 

    ADC register values

    SPI Data (When issue happens is as below):

    2 : FF

    F : FF

    40 : FF

    0 : 81 // Specifies the conversion completed immediately

    44 : FF

    0 : 0 // Issue here

    0 : 0 // Issue here

     

    SPI Data (When no issue happens):

    2 : FF

    1F : FF

    40 : FF

    0 : 1

    40 : FF

    0 : 1

    40 : FF

    0 : 1

    40 : FF

    0 : 1

    40 : FF

    0 : 1

    40 : FF

    0 : 1

    40 : FF

    0 : 1

    40 : FF

    0 : 81 // Shows conversion completed

    44 : FF

    0 : 0

    0 : 1F // Data good here

    We do not have access to Ready pin and use Ready Status instead 

    SPI Capture Image 

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  • Thank you for responding. 

    ADC register values

    SPI Data (When issue happens is as below):

    2 : FF

    F : FF

    40 : FF

    0 : 81 // Specifies the conversion completed immediately

    44 : FF

    0 : 0 // Issue here

    0 : 0 // Issue here

     

    SPI Data (When no issue happens):

    2 : FF

    1F : FF

    40 : FF

    0 : 1

    40 : FF

    0 : 1

    40 : FF

    0 : 1

    40 : FF

    0 : 1

    40 : FF

    0 : 1

    40 : FF

    0 : 1

    40 : FF

    0 : 1

    40 : FF

    0 : 81 // Shows conversion completed

    44 : FF

    0 : 0

    0 : 1F // Data good here

    We do not have access to Ready pin and use Ready Status instead 

    SPI Capture Image 

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