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Microcontroller Programming » Oscilloscopes - which one should I get for examining SPI transmissions?

September 20, 2012
by jlaskowski
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I am using SPI to talk to another chip and the other chip doesn't seem to be responding properly. It was suggested that I get an Oscilloscope readout of the CS, MOSI, and MISO lines. I have never owned or used an oscilloscope. What kind should I get or what features do I need? I would think I'd want to be able to examine multiple lines at the same time.

September 20, 2012
by Ralphxyz
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jlaskowski, there are some interesting/informative oscilloscope discussions here in the Nerdkit forum.

I have a 100 Mhz scope and a Data analyzer both are really nice.

I would seriously look at the the PC based oscilloscope/data analyzer as you get lot of utility and you already have a pc.

Rlph

September 20, 2012
by Noter
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If I was looking to buy now I'd probably go for this one - https://www.sparkfun.com/products/8938

September 20, 2012
by jlaskowski
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I'm watching a video on the sparkfun data analyzer you suggested. Very slick for the price!

September 20, 2012
by jlaskowski
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Is the fact that it's highest frequency is 24 MHz a problem? I've read that the frequency should be 5x the signal frequency. If my ATMega is running at 14.7 MHz and my SPI is clocked at f/2, so 7.35 MHz, then 24 MHz would be less than 5 times f.

September 20, 2012
by Noter
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I don't know about the 5x recommendation but I guess you could debug your program and circuit at a lower rate and then bump the clock after it's working. The problems I've run into have not been because of the clock setting.

I agree that it looks good for the price. I have a MSO-19 which is about $100 more and has a digital oscilloscope feature included. I like it but I'm sure I could have gotten by with the less expensive analyzer.

September 20, 2012
by JimFrederickson
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It is always good to be able to "over-sample" your signal. 5x is considered good enough for most applications.

That being said.

If you are having problems the first thing that should be done is to "simply the problem as much as possible"...

I would think, that in this case, the first step I would take is to slow down the SPI Communications as much as possible.

Does the SPI really need to be at f/2 for finding your problem?

The faster things are running, the more possible problems there are.

Also are you absolutely sure that the device you are talking is able to run that fast? I have found many SPI Devices that have quite varied maximum bit rates.

September 21, 2012
by Ralphxyz
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jlaskowski, if you are still looking for a oscilloscope I like Noter,s MSO-19 or a similar PC/USB combo unit.

Ralph

September 21, 2012
by jlaskowski
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I actually tried a slower clock, but that didn't work. I also tried changing the CPHA to see if that would help, but it did not.

I ended up buying the one Noter recommended (had it next day shipped), and it works awesomely! Very easy to set up and the software is so easy to use. I just watched the video they have on how to use the software...piece of cake.

Thanks, Noter!

October 12, 2012
by scootergarrett
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I got the DOS nano for $100 and it worked great until I sat on it, down side for a pocked oscilloscope. It still works but I had to make a new charging cable.

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