Oscilloscope problem or noise or what

Thread Starter

majd-ghadab

Joined Dec 25, 2012
23
Hello everyone,
i bought a couple of weeks ago Rigol oscilloscope 300 Mhz 2Gsa/s because i would like to work with low rf frequencies.. anyway.
i work also with microcontrollers .. the problem is when i see the Spi data bus 5.5 Mhz the speed of Spi as set in Cubemx the output looks like the picture.
the circuit is working that means the square wave is correct but why it looks like this . please help
is there a problem with my oscilloscope?
i know i need a lot of samples to see squarewave more than sine but is this not enough 300mhz 2gsa/s !!
 

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MrChips

Joined Oct 2, 2009
30,707
Is your oscillator probe set to 10X attenuation?
How and where is the grounding clip of the oscillator probe connected?
Make sure that you connect the grounding clip to a GND location close to the SPI signal source.
 

Thread Starter

majd-ghadab

Joined Dec 25, 2012
23
thank you all for your replies
i am waiting for the probes and they shipped to me..
i am using a cheap connector !!
when the probes come i will post whay will happened. Thanks
 

Wuerstchenhund

Joined Aug 31, 2017
189
Hello everyone,
i bought a couple of weeks ago Rigol oscilloscope 300 Mhz 2Gsa/s because i would like to work with low rf frequencies.. anyway.
Well, I really hope you got this scope really really cheap (i.e. <$200) because the Rigol DS1302CA has been out of production for over 5 years now. Also, it's specs are pretty poor (only 10kpts memory which is laughable, shitty low-res screen, very low update rate, no serial decoders).

i work also with microcontrollers .. the problem is when i see the Spi data bus 5.5 Mhz the speed of Spi as set in Cubemx the output looks like the picture.
the circuit is working that means the square wave is correct but why it looks like this . please help
is there a problem with my oscilloscope?
As the others said probably user error. You didn't provide any details as to how you probed the signal so it's hard to tell what you did wrong.

i know i need a lot of samples to see squarewave more than sine but is this not enough 300mhz 2gsa/s !!
300Mhz BW and 2GSa/s are generally more than enough to capture all relevant parts of a 5.5MHz SPI signal, however because your scope has so little memory the sample rate may drop quickly to become insufficient for resolving the actual signal (i.e. with single ch mode anything longer than a 5us segment means your sample rate and with that your usable BW will drop). However, the image shows as timebase setting of 50ns/div which at 12 divisions is a time span of 600ns so the sample rate should not be a problem here.

Tell us a bit more about your probing technique.
 

rsjsouza

Joined Apr 21, 2014
383
Well, I really hope you got this scope really really cheap (i.e. <$200) because the Rigol DS1302CA has been out of production for over 5 years now. Also, it's specs are pretty poor (only 10kpts memory which is laughable, shitty low-res screen, very low update rate, no serial decoders).
Wuerstchenhund, it could well be the much newer DS2302A.
 
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