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Why does the transition detector behave differently in the new TLA7Nx/Px logic analyzer modules compared to the older TLA7Lx/Mx logic analyzer modules?

Question :

Why does the transition detector behave differently in the new TLA7Nx/Px logic analyzer modules compared to the older TLA7Lx/Mx logic analyzer modules?

Answer :

The LA modules can be programmed to recognize the transition of an individual channel or a group of channels. For example, "If Channel ABC Goes High then Trigger", or "If Group XYZ Changes then Trigger". Internally, this is done using a transition recognizer which compares values at consecutive sample points. Although you would expect the output of this transition recognizer to be "false" for the first sample in an acquisition (because there is not a previous sample to compare with), the transition recognizer output is actually sometimes "true" for the first sample. This means that if your trigger program is "If Channel ABC Goes High then Trigger" you may get a trigger on the first sample even though you would probably not expect this.

The workaround is to use a state in the trigger program to skip over the first sample, the sample for which the transition recognizer output is unreliable. The modified trigger program would look something like this:

State 1: If Anything then Go To State 2

State 2: If Channel ABC Goes High then Trigger

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FAQ ID 60261

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