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Jon Magin - Honorable Mention (Troy, Ohio)
Logic Analyzer
Downloads for this project:
All files and information © 2006 Jon Magin.
Project Description:
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Click on Image for a close-up
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The challenge I undertook was to create a logic analyzer with readily obtained low-lost hardware and a modular software design to allow for expansion and changes.
To provide useful analysis, a logic analyzer must record changes in the states of the signals under observation. This requires a fast system clock. The Parallax SX48 with clock rates of 75MHz and higher is a great match for this function! Its speed and built in hardware are more than sufficient to keep up with most of the signals I need to process.
Most logic analyzers over-sample the signal states at an extremely high rate. A benefit to using an SX for this type of analysis is that its internal circuitry makes over-sampling completely unnecessary! The SX is not limited by the Nyquist sampling rate since it does not need to “sample” signals in order to detect changes in them.
A second benefit to using the SX with its internal state-change detection circuitry is that only samples of actual state changes need to be recorded. Typical logic analyzers record millions of samples per second many of which are duplicate copies of existing states. This is not an efficient use of memory! Using the SX provides a significant form of data "compression" over typical designs by making it possible to store only state changes and the time of the changes eliminating the need for external high-speed RAM.
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Click on Image for a close-up
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As with all logic analysis, accurate timing information is critical. Here, once again, the SX48 special hardware to keep accurate time without burdening the main processor. This advantage comes in the form of an independently running timer, of which the SX48 has two. Keeping track of elapsed time on the SX48 could hardly be easier!
Using these advantages a logic analyzer has been created that is capable of recording sixty-three 8-channel state changes at speeds up to 400KHz. In keeping with the low-cost goal of the design I chose to implement this using an SX48 Proto Board ($10) with a 50Mhz ($2) resonator along with an LCD AppMod ($15) for the user interface. All that is required in addition to these three components is a power supply (a 9-V battery will work) and some wire for signal connections.
This design utilizes the processing speed and hardware capabilities of the SX48 to the extent that the only external hardware required is the SX support circuitry and the user interface device. The result is a low cost logic analyzer consisting primarily of three easily obtainable parts and some analysis software!
If nothing else, this has been a valuable learning experience for me. I hope it will be a beneficial example to others who may examine this design.
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