I've been playing around with I2C decoding and I think it should be similar to CANbus. Here's what I do:
First, set the scope mode so that pressing the horizontal timescale knob switches to Zoom mode (instead of fine adjust). Settings -> Utility -> Setup : Fine/Zoom=Zoom
Next, setup Settings -> Decode : I2C, and turn on Bus Status
Now, hit run and adjust the horizontal time base to capture as much as possible while still seeing something in the decoded protocol area. Note: if you go slower than 20ms/div (i.e. scrolling display), protocol decode is disabled and you'll need to go back to the previous step to turn Bus Status back on. Hit the stop button when you have a reasonable capture. In my case, I have two I2C bursts over 100ms (the code is running 10x per second I2C polling rate).
Press the horizontal time scale knob to switch into Zoom mode, then use the horizontal position knob and the time scale knob to display a burst of I2C activity
To view the earlier I2C burst (on the left of the capture), zoom back out using the time scale knob, then using the touchscreen, drag your finger on the zoomed display to shift it back to the first I2C burst. Zoom in and drag as needed to view the earlier I2C burst
Let me know if this isn't clear enough, and more importantly, does this work for CANbus too?
-Bob