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What do the thick white lines on the digital channel edge transitions indicate?

Question :

What do the thick white lines on the digital channel edge transitions indicate?

Answer :

The thick white line on a signal edge indicates that there are more transitions than can be displayed at the current magnification. Effectively, we decimate the acquisition data whenever the display has a ratio of more than one sample per pixel. So for example if I had 10,000 sample points and only 1,000 pixels, I would effectively be showing only every tenth sample. Thinking of it from the other direction, I could say that I have ten samples displayed in every pixel.

The display algorithm looks at the ten samples to be displayed in a given pixel and if there is an edge in the ten samples it will place an edge in that pixel. If it finds two samples among the ten with edges it will color the edge it places in the pixel white. This gives the user notice that the display is effectively aliasing the data.

Figure 1

Figure 1: Display of Multiple Edges, and the same edges when zoomed in

Furthermore, the white edge alias notification is only relevant relative to the data memory being displayed. By this I mean that if we are displaying the main memory, and there were glitches that weren't captured by the main memory, then it will not display a white edge. The display of the main memory isn't being aliased, so there is no need to show a white edge. Thus the minimum detectable pulse width doesn't determine white edge placement.

Wave Inspector will search the contents of whichever memory (Main versus MagniVu) is being displayed. So it doesn't find narrow pulses in the main memory when it is displayed because there aren't any in the main memory. It does find them in the MagniVu memory when it is displayed because they are there.


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FAQ ID 53151

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