How to Use a Logic Analyzer

- some of the key elements in using a logic analyser: how get the best from it for testing complex logic / digital circuits and boards.

Although the operation of a logic analyzer may appear to be fairly complicated at first sight, a methodical approach to the use of one enables it to be set up correctly and to be used effectively. Once the probes are connected, the logic analyzer is programmed with the names of each signal. The analyzer can also associate several signals into groups so that they can be manipulated more easily.

With the basic set-up of the logic anlyzer complete the capture mode for the data needs to be chosen. This can be set to one of two modes:

  • Timing mode     Using this mode signals are sampled at regular intervals based on an internal or external clock.
  • State mode     Here one or more of the signals are defined as clocks, and data is sampled on the edges of these clocks.

Once the logic analyzer mode is chosen then the trigger condition can be set. The analyzer trigger condition may vary from a very simple signal edge to a set of conditions that must be met across a variety of lines. The complex trigger conditions aid in locating problems that occur when a particular set of conditions occur.

With the trigger condition set, the logic analyzer can be set to run, triggering once only, or repeatedly. The data that is captured can then be displayed and analysed.

Logic analyzers are an essential tool for many applications where digital circuits employing a large number of lines that need to be monitored. They are used to assist in the development of many of the circuits involving digital hardware and software. By using a logic analyzer is it possible to be able to look at these lines in a practicable fashion and be able to trigger on a preset pattern of a given number of lines. In this way the events that happen after a predetermined occurrence can be viewed for investigation. This is invaluable in enabling fault finding of complex software driven circuits.

Although with the enormous increase in the complexity of circuits, other techniques are often applicable, logic analysers are still used for many applications

By Ian Poole

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