In my designing, we use FPGA to drive AD5757 chip with SPI port.
FPGA -> ADUM1401 -> AD5757, an sample connection, SPI line have no any pull up or down resistor.
FPGA can communication correctly with AD5757, but when test the SPI waveform on AD5757 SPI line(behind the ADUM1401), looks the waveform is strange.
The CAP of oscilloscope probe is 3pf.
Grid is 40uS.
Blue line is the CS line, it down near to 1V from 5V, then, becom very slow down to 0V, other line also have this cause.
I have no found any issue for the oscilloscope probe.
Could you help to analyssi whether this waveform is correct.
Blue line: CS
Purple line: CLK
Green line: DIN of AD5757
Yellow line: Dout of AD5757
Can you share the exact schematic used?
Have you tried removing the AD5757 then check again the SPI waveforms?