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AD5932 FSYNC / Compatibility with other SPI Devices

Question asked by jstein on Feb 28, 2012
Latest reply on Mar 1, 2012 by jstein

Hey,

I'm using the AD5932 together with the NI 8451 USB/SPI converter. Using the AD5932 on the SPI Bus works just fine, I can setup a frequency sweep and control the increments using the CTRL Pin.

 

With another device attached on the SPI-BUs I can still programm the AD5932and also the frequency increment works. BUT if I try to read/write another device the AD5932 resets itself to the programmed frequency.

 

As an example:

1) Programm the AD5932 for a sweep from 1Mhz to 5Mhz in 1Mhz steps

2) Cyle the CTRL Pin 3 times - > Output frequency 3 Mhz

3) Read/Wirte another SPI Device on the Bus -> Output frequency 1 Mhz

 

I'm using the FSYNC as a chip select Signal, so during communcation with another Bus member it is HIGH. What I think is happening is that the AD5932 ignores the FSYNC signal for some reason, sees Data on the bus that dont make sense for him and resets itsself to the last programmed status.

 

Obviously I already check if the FSYNC stays HIGH, tied it to VDD manually etc.....

Maybe as a first step someone can confirm that in theory the AD5932 can be used with other devices on the Bus.

 

Thanks for any advice!

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