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How to read data from AD7609 (EVAL-AD7609)?

Question asked by Zirbel on Jan 19, 2016
Latest reply on Jan 19, 2016 by Gnib

I am trying to read data from the AD7609 using the Eval-AD7609 board and an FPGA.  I have made a number of modifications to the board to use it without the "CED Board Connector".

1) SL9 and SL10 --> VDRIVE and AVCC on board connectors (5V each)

2) SL7 & 8 --> bring the data out to on-board SMB pads

3) R3/R4 --> Serial mode

 

I am trying to read the data during conversion but never see that the BUSY pin falls low.  I also never see the FRSTDATA pin go high.

 

My timing sequence is as follows (verified using a scope):

1) RESET high for 2.5 microseconds

2) RESET low for ~2.5 microseconds (us)

3) CONVST A & B Low for 50 nanoseconds (ns) (check if BUSY is high before continuing to CS low)

4) CS low & wait for FRSTDATA to go high    <------FAIL (FRSTDATA never goes high)

5) Timeout and go back to RESET (step 1)

 

If I trick my FPGA into thinking FRSTDATA went high,

I read out 0x00000 on all channels of DATA A (1-4) and 0x3FFFF on all channels of DATA B but BUSY never falls

 

Is there some behavior of the chip that is not specified to start it up correctly? For example, am I supposed to allow it to convert on the first read without trying to read the (non-valid) data at Step 4 (from above)?

 

Any help is appreciated.

Thanks

 

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