Hardware Debugging Tools

Updated on 2017/08/11 16:53

Syllabus

  • Hardware debugging tools (timing analysis using logic analyser)

Logic Analyzer

It is separate electronic instrument used to solve both hardware and software problems  by simultaneously observing the various signal on screen
A logical analyzer is basically a multichannel oscilloscope
Logic analyzer takes input samples and stores it in its own internal memory

COMPARISON OF OSCILLOSCOPE AND LOGIC ANALYZER
OSCILLOSCOPELOGIC ANALYZER

 

Oscilloscope is used for measuring analogue waveforms: amplitude, phase values, or edge measurements such as rise times, etc.

Typical oscilloscope applications:

  • Investigating waveform shapes, ringing, rise time, etc.
  • Characterise aspects like waveform jitter and stability.
  • Measure signal amplitudes.
  • Detect transients, and unwanted pulses.

 

A logic analyser is used for verifying and debugging the operation of digital designs looking a logic states and timings.

Typical logic analyser applications:

  • Investigate the system operation.
  • Correlate a large number of digital signals
  • Detect timing violations
  • Trace embedded software operation.

Block Diagram

Logic-Analyser-Block-Diag.svg

Fig. Block Diagram of LOGIC Analyzer

Block diagram Explaination

  • The data on parallel 32 input channels is compared with adjustable threshold voltage to decide the logic level of the input data
  • Input data is stored in memory, when trigger occurs data sample stored in memory are displayed on CRT screen
  • The trigger can come from external source or from a word comparator block
  • A word comparator block compares input data word which is selected by user through 32 switches
  • when two word match the word comparator block will trigger the signals

LOGIC analyzer types


Modular Logic Analyzer

It consist of both a chassis or mainframe and logic analyzer modules. The mainframe/chassis contains the display, controls, control computer, and multiple slots into which the actual data-capturing hardware is installed. The modules each have a specific number of channels, and multiple modules may be combined to obtain a very high channel count. While modular logic analyzers are typically more expensive, the ability to combine multiple modules to obtain a high channel count and the generally higher performance of modular logic analyzers often justifies the price. For the very high end modular logic analyzers, the user often must provide their own host PC or purchase an embedded controller compatible with the system.

Portable Logic Analyzer

It is also referred to as standalone LAs. Portable logic analyzers integrate everything into a single package, with options installed at the factory. While portable logic analyzers generally have lower performance than their modular counterparts, they are often used for general purpose debugging by cost conscious users.

PC-based Logic Analyzer

The hardware connects to a computer through a USB or Ethernet connection and relays the captured signals to the software on the computer. These devices are typically much smaller and less expensive because they make use of a PC's existing keyboard, display and CPU.
 

Triggering modes

Triggering from external inputs allows to observe the data smaples at a perticular event to do this user has to program logic analyzer into

  1. Pre-trigger mode
  2. Central trigger mode
  3. Post-trigger mode

Display formats

Provide a time display of logic states:   Logic analysers possess a horizontal time axis and a vertical axis to indicate a logic high or low states. In this way a picture of the digital lines can be easily displayed.

Multiple channels:  
Logic analyzers are designed to monitor a large number of digital lines. As logic analyzers are optimised for monitoring a large number of digital circuits, typically they may have anywhere between about 32 and 200+ channels they can monitor, each channel monitoring one digital line. However some specialised logic analyzers are suitably scaled to be able to handle many more lines, and in this way enable tracking and fault finding on much more complex systems.

Displays logic states:  

The vertical display on the analyser displays the logic state as a high of low state. The signals enter the various channels and are converted into a high or low state for further processing within the analyser. It provides a logic timing diagram of the various lines being monitored.

Does NOT display analogue information :  

These test instruments do not present any analogue information, and in this way they differ from an oscilloscope. They are purely aimed at monitoring the logic operation of the system. If any analogue information is required, then an oscilloscope must be used in addition.
 

References

  • Notes by Prof Sujit Wagh, SKNCOE, Pune
  • WikiNote Foundation
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Created by Vishal E on 2017/08/10 19:32