AD7699: Sharing SPI bus

Hi, I have a couple of question about using an AD7699;

Some background: Basically I'm developing a product where we need to sample two channels of the AD7699 at very specific time intervals (around 40uS), so I'll be using an timer interrupt to control when the CNV line goes high, then once the two channels have been sampled I don't want the AD7699 to start another sample until the next timer interrupt triggers, so would assume that I should keep the CNV line low until this happens?

However if the CNV line is low and I need to communicate with another device (possible an AD5765) on the same SPI bus, is this going to have any affect on the AD7699. From what I understand once the AD7699 has seen the first 16 (or 30 if doing a CFG readback) SCK cycles then it has no further interaction with the SPI bus until it's done another conversion.

Would appreciate anyone advice on if this is possible or if I need to have a single SPI bus just for the AD7699.

Thanks

John

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  • Hi John,

     

    The busy indicator is enabled at the EOC if CNV is low and SDO is returned to low. In addition, to generate the busy indicator properly, the host must assert a minimum of 17 SCK falling edges to return SDO to high impedance because the last bit on SDO remains active as shown in figure 38. After you have clocked (17 or 31 SCK cycles) out the current conversion data, keep the CNV low and then you can use this SPI bus to communicate with another device as long as you don't start the next convesion.

    Regards,

    Maithil

Reply
  • Hi John,

     

    The busy indicator is enabled at the EOC if CNV is low and SDO is returned to low. In addition, to generate the busy indicator properly, the host must assert a minimum of 17 SCK falling edges to return SDO to high impedance because the last bit on SDO remains active as shown in figure 38. After you have clocked (17 or 31 SCK cycles) out the current conversion data, keep the CNV low and then you can use this SPI bus to communicate with another device as long as you don't start the next convesion.

    Regards,

    Maithil

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