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Multiple AD5293 In SPI Bus Not Reading

Question asked by XxDarkLightning on Aug 10, 2012
Latest reply on Aug 13, 2012 by XxDarkLightning

Hello,

 

I have successfully written and read to a single AD5293 using LabVIEW. I now have three AD5293 wired into a SPI Bus format (http://upload.wikimedia.org/wikipedia/commons/f/fc/SPI_three_slaves.svg)  and can write okay as I can measure resistance and see that is changes, but cannot read back on any device. With the pull-up resistor on the SDO line at 2.2k in both single and multiple chip scenarios, the line is not at +5V initially and actually fluctuates between a high and low states depending on what value I read back. The only way I can read with multiple devices is to explicitly place each device in high impedance mode. I didn't have to do that with the single chip. Does anyone have insight as to why I need to add this extra step with three, and if there is a way I can get around it. Thanks.

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