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AD7686 SPI question regarding conversion

Question asked by Lionelwallace Employee on May 19, 2014
Latest reply on May 22, 2014 by Lionelwallace

I received this question from a customer:

 

I’ve attached a picture of the logic analyzer capture. I have two questions.

  1. Am I preforming the acquisition/conversion correctly? I have from to read a bunch of analog values. The time to read each analogue value is when the trigger pin goes low. I have about 1.75us to read this pulse. My logic is to hold the conversion pin low so the ADC is constantly sampling. An interrupt catches the falling edge of the trigger pin and I start a conversion (Conversion pin tied to CONV). I hold that pin high for 4.5us. Finally, I bring that pin low and read the values.

 

  1. The SPI read doesn’t go low between reading bytes. I don’t see that all the time. Is that normal?

 

I have the SPI clock set at 8MHz. This is the fastest we’ve tried running it. This gives me an acquisition time of 1.71us.

 

See scope screen shot attached

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