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Logic Analyzers Exclusive Hands-On review
PC-based logic analyzers can reveal much about digital signals. Here's the low-down on seven models we tested.
Jon Titus -- Design News, November 21, 2005
Logic analyzers capture digital signals and display state information, timing information, or both.
When testing or troubleshooting electronic equipment, engineers use these instruments to extract microcontroller timing information, monitor sequences of digital events, watch instructions go to and from a microprocessor, and so on. Wherever you need to monitor sequences of bits and bytes, you'll find a logic analyzer fills the bill. In addition to watching the usual flow of signals on parallel lines, some logic analyzers can decode I2C, SPI, CAN, and other serial protocols. And, if you plan to debug an embedded computer, you also can decode instructions so you can watch the flow of a program, step by step, as op-code abbreviations go by on a screen.
Logic analyzers traditionally fit into large desktop enclosures, but several manufacturers now offer small "pocket size" logic analyzers that rely on a host PC for display, control, and storage capabilities. We tested seven of these instruments and report our results for you here. Tests involved the use of a standard microcontroller development kit and simple programs written in C.
I found several areas of concern to keep in mind while evaluating these or similar instruments in your lab.
Connections: Several analyzers come with small grabber clips. Connecting to eight signals on a row of pins spaced at 0.10-inch intervals provides a challenge. Other instruments provided a choice of female contacts that push onto 0.025-inch2 pins. If you need to probe fine-pitch contacts, keep your connection options in mind.
Triggers: All logic analyzers in this review provide triggering, because that's what logic analysis is all about: You want to see what happens when a specific event occurs. Unfortunately, some analyzers provided triggers that only acted on logic levels and in one case, I could only set up a trigger based on four signals. These days, analyzers need level and edge triggering and some engineers will need sequential triggers such as, "trigger if condition A follows condition B." Know your triggering requirements so a purchase doesn't disappoint you.
Cursors: These movable marks that locate signal features proved troublesome in many displays. Software should give you complete control over cursors and should show you where the cursors are, how to control them, and the time mark they represent in a display. The capability to calculate the time between sets of cursors makes them particularly valuable. Cursors should not get "lost" on a display so you have to go look for them. And lastly, you cannot have a good logic analyzer without solid documentation.
To read Jon Titus' review of logic analyzers, click here (PDF format).
Check out Jon Titus' in-depth evaluation of these analyzers at:
http://rbi.ims.ca/4401-556
Contributing writer Jon Titus can be reached at jontitus@comcast.net
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