need help viewing non-periodic digital signal on oscilloscope

Discussion in 'General Electronics Chat' started by count_volta, Oct 4, 2011.

  1. count_volta

    Thread Starter Active Member

    Feb 4, 2009
    435
    24
    I am trying to view i2c signals on the expensive as heck oscilloscope at work and am having problems.

    Two signals on two channels. Clock and Data.

    I have two devices communicating with each other using i2c. The master sends a request to the slave and the slave replies. This only happens once and for about a second. It happens every time I power up both devices.

    I tried different triggering modes and triggering on the clock and data lines and etc. It feels like I tried everything. No matter what, I see the two digital signals appear for a second and they are gone. I need to catch them so that I can analyze them.

    Here is the scope I am using. http://www.testequity.com/products/3580/

    It actually has an i2c bus mode and automatically converts the clock and data into hex values right above the signals. I have used it before and successfully. But in order to use it, I first have to catch the signals.

    If you don't know how i2c works, its a serial communication protocol with voltages 0-5V and has speeds in the kHz range.

    Can you please give me some advice on how to catch my signals?

    Much appreciated.
     
  2. The Electrician

    AAC Fanatic!

    Oct 9, 2007
    2,287
    331
    It sounds like you need to use the "single" capture mode.
     
  3. count_volta

    Thread Starter Active Member

    Feb 4, 2009
    435
    24
    I have already tried the single capture mode. If I set the trigger on the clock for example, and do single capture, I get only a tiny piece of my waveform.

    I get this.

    [​IMG]

    But I want this....

    [​IMG]

    I have read the scope manual but its extremely confusing. Is there something I can change so that single capture gets the entire waveform and not only a piece?
     
  4. The Electrician

    AAC Fanatic!

    Oct 9, 2007
    2,287
    331
    This scope has a 20 Megapoint record length on all channels. You need to make the time per cm longer. With 20 Mpoints, after the capture happens you can decrease the sweep speed and look at the captured data in detail.
     
  5. hspalm

    Active Member

    Feb 17, 2010
    201
    8
    If there's a knob called "horizontal scale", turn it to the left
     
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