SPI Signal Shape Issue

[AE104]

Hello,

I am try to control an external DAC system with the SPI interface. The clock signal shape looks like the attached file. I didn't figure out the meaning of the signal. Yellow is the clock signal and the blue is CS signal.

[Tesla DeLorean]

Yes, looks awful, how is this wired up? Show a circuit diagram

Make sure the grounds are properly bonded across domains.

[AE104]

The reference manual of the chip is designed with the isolator, so I designed it based on that. Should I remove it? @Community member​ 

[Tesla DeLorean]

And with the scope traces, which side are you probing here?

And which ground is the scope attached too?

[AE104]

I am probing the OUT side of the isolator. The yellow signal is the SCLK, and the blue is CS. The probing to the GND_ISO.

[waclawek.jan]

Why is scope set to 25MSa/s?

JW

[AE104]

I assume it is default setting. Should I change it? If it is, how can I do that?

[AScha.3]

yes. Need to change to something useful. set -> button Aquire-> mode:normal, mem-depth: auto , anti-alias:off ; + buton Display -> type: vector .

+

set your probe to x10 , an in dso probe menu also x10 setting.

(and it was NOT default setting ! )

if want some gaming: just try -- press button AUTO , with signal active; scope tries to set it then automatic good.

[AE104]

Now I just reflected your recommendations. These are the current signal shapes.

I will try to test without the isolator.

[AScha.3]

mmmm. something wrong - my sample rate is 500Ms at 2us/div.

(i have same DS1054 here, just 200MHz software in :) )

you have something totally wrong in settings - i cannot set so (useless) low rate , its greyed out.

did you try: AUTO button ? (or try: CLEAR , then AUTO , with active input signals)

here ...why dont use the dso print file ?? so:

[AE104]

I pressed the CLEAR and AUTO, now the sampling rate is 250 MSa/s with 300k pts.

[Tesla DeLorean]

The bandwidth of the isolator is 25 Mbps

Is the signal on the STM32 side clean? Not ringing?

If the traces are short, ease back the slew-rate via SPEEDR settings.

What speed is your SPI clocking at?

[AE104]

Now the updated signals look like the attached figures (the isolator removed).

The SPI Baudrate 10.5 Mbits/s.