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when AD7708 changes the channel,which channel's data is in the data register?


I have a problem.  If the AD7708 just starts convertion of the first channel, before the convertion is not completed.I send  the command of startting the second channel. 

and then when the convertion is complete, wich channle's date is in the data register?  first channel or second ?

Then I have done a experiment ,I find that the resault is The First channel.

My true needs is that,I want a fixed channel starts a new convert immediately. Tks!

  • Hi, 

    The part has only one data register, so each channel is just sharing this register. So if you are in continuous conversion mode, the part continuously converts on selected channel until the nRDY goes low indicating the completion of the conversion and means that the data register is updated with this value. So the time the nRDY goes low depends on the settling time and update rate. So if you are only converting on a single channel the settling time is only required at the first conversion and the following conversion will be updated at the programmed update rate. But if you are converting multiple channels then each channel conversion will require the complete settling time. This is an old part so I am not if there is an automatic sequencer that required in your application. 

    So I would recommend to use our new products such as AD7124-4B for example as it allows to enabled multiple channels and  the ADC automatically sequences through the enabled channels, performing one conversion on each channel. The data register is updated as soon as each conversion is available and this can be monitored using the DRDY pin or RDY bit. The user can then read the conversion while the ADC converts the next enabled channel.



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