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AD7984 (EVAL-AD7984-PMDZ) SDO signal stuck

Question asked by Martin336 on Feb 26, 2016
Latest reply on Feb 29, 2016 by Brandon
Branched to a new discussion



I am trying to talk to EVAL-AD7984-PMDZ from ZedBoard and I am observing unexpected behavior. I am feeding the board with 1 MHz clock with CNV held high for about 30 cycles, but I dont get any readings from SDO pin. It is either high or low all the time, I got the following waveform from logic analyzer:

     red (top) - CNV pin

     brown (middle) - SDO

     white (bottom) - SCK


I have tried to tie a pullup and pulldown resisotrs (internal on the zedboard), to the SDO pin, the above waveform is with pullup.


The PMOD connector is configured according to following pinout (EVAL on the left, ZedBoard PMOD header on the right):


The following is the constraint file setting up the pins:

set_property IOSTANDARD LVCMOS33 [get_ports {PMOD_CNV}]

set_property IOSTANDARD LVCMOS33 [get_ports {PMOD_SDO}]

set_property IOSTANDARD LVCMOS33 [get_ports {PMOD_SCK}]


set_property PACKAGE_PIN Y11 [get_ports {PMOD_CNV}]


set_property PACKAGE_PIN Y10 [get_ports {PMOD_SDO}]


set_property PACKAGE_PIN AA9 [get_ports {PMOD_SCK}]


ZedBoard automatically provides 3V3 on VCC pins (measured). I am not providing any external input to the board (anyway, the behavior of SDO is not according to datasheet). The EVAL board was plugged into ZedBoard when the FPGA was already programmed and running. I got 2 identical EVAL boards, the same for both of them. I cant think of any additional relevant information.


Any idea what to do ? Does my testing prove the boards are bad ?