Basic introduction of the hottest logic analyzer

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Basic introduction of logic analyzer

Abstract: This paper introduces the basic concept, historical origin and development, basic classification, technical indicators and basic functions of logic analyzer, and introduces the differences and connections between logic analyzer and oscilloscope. Through these, it introduces the basic knowledge of logic analyzer

key words: timing analysis state analysis record length

logic analyzer is a waveform test equipment similar to oscilloscope. It can monitor the logic level (high or low) when the hardware circuit is working, store it, and express it intuitively in the form of graphics, which is convenient for users to detect and analyze errors in circuit design (hardware design and software design). Logic analyzer is an indispensable electronic test equipment in the design. Through it, we can quickly locate errors, solve problems, and achieve twice the result with half the effort

I. production and development of logic analyzer

microprocessor was developed in the early 1970s, with 4-bit and 8-bit bus. The dual channel input of traditional oscilloscope cannot meet the observation of 8bit. The testing of microprocessors and memories needs to be different from time domain and frequency domain instruments, so data domain testing instruments came into being. Not long after HP launched the state analyzer and biomation launched the timing analyzer (they were very different at first), users began to accept this digital domain test instrument as the final means to solve the digital circuit test. Soon, the state analyzer and timing analyzer were combined to form a logic analyzer

in the late 1980s, logic analyzers became more complex and more difficult to use. For example, multilevel tree triggering is introduced to deal with complex events such as conditional statements such as if, then, else, etc. This kind of combination trigger will certainly raise the broach to the top, but it is more flexible, and it is not so easy for most users to master

The basic development trend of logic analyzer is the continuous integration of computer and instrument. Using windows on the PC platform, as long as the correct software and related tools are given, remote control can be carried out through interconnection, source code and symbols can be extracted from the target file format, and the processor can run various control operations

II. Classification of logic analyzers

at present, there are two types of logic analyzers in the market. One is independent logic analyzer, and the main suppliers are Agilent and tech; The other is PC based virtual logic analyzer (VI), which is relatively cheap. The main supplier is national instruments (Ni), and the main product is graphical test and measurement programming software LabVIEW. Traditionally, LabVIEW software running on PC is called virtual instrument, but with the launch of LabVIEW RT, these VI can run on a variety of devices, such as portable instruments, industrial PC or web-based instruments

there are also some manufacturers of logic analyzers in China, but most of them are virtual instruments. Due to the high price of imported independent logic analyzers, there is a great need for an independent, portable and simple logic analyzer in China. A logic analyzer produced in Taiwan and launched by Beijing ocean is more suitable for the domestic market

III. main technical indicators of logic analyzer

1. Number of channels of logic analyzer

where a logic analyzer is needed, to comprehensively analyze a system, all signals that should be observed should be introduced into the logic analyzer, so that the number of channels of the logic analyzer should be at least: the word length of the system under test (number of data buses) + the number of control buses of the system under test + the number of clock lines. Thus, for an 8-bit computer system, at least 34 channels are required. At present, the number of channels of mainstream products of several manufacturers is as high as 340, such as Tektronix. The mainstream product on the market is a 34 channel logic analyzer, which is used to analyze the most common 8-bit system. For example, the Ola series logic analyzer newly launched by Beijing ocean is a 34 channel logic analyzer

2. Timing sampling rate

in timing sampling analysis, we should have a sufficiently high timing analysis sampling rate if we want to have sufficient timing resolution. However, it is not only high-speed systems that need a high sampling rate. Now the sampling rate of mainstream products is as high as 2gs/s. At this rate, we can see the details of 0.5ps time

3. State analysis rate

during state analysis, the sampling reference clock of the logic analyzer uses the working clock of the tested object (the external clock of the logic analyzer). The highest rate of this clock is the high state analysis rate of the logic analyzer. In other words, the logic analyzer can analyze the fastest working frequency of the system. The timing analysis rate of current mainstream products is 300MHz, up to 500MHz or even higher

4. The recording length of each channel of the logic analyzer

the memory of the logic analyzer is used to store the sampled data for comparison, analysis and conversion (such as converting the captured signal into a non binary signal)

5. Test fixture of logic analyzer

the logic analyzer is connected with the tested device through the probe. The test fixture plays a very important role. There are many kinds of test fixtures, such as flying head and fly head

IV. comparison between oscilloscope and logic analyzer

1. The characteristics of oscilloscope are:

a) it can check the small voltage change of signal

b) has high accuracy of time interval measurement

oscilloscope is usually used when high vertical resolution and high voltage resolution are required. In other words, if you need to observe small voltage changes, you should use an oscilloscope. Many oscilloscopes can provide high resolution of the selected time interval of the range of instruments and equipment, so they can measure the time interval of two events with high accuracy. In short, you should use an oscilloscope when you need parameter information

2. The characteristics of logic analyzer are:

a) it can observe multiple signals at the same time

b) be able to view the system signal of the hardware system

c) it can trigger multiple signal lines according to the high and low level mode and check the results

the working mode of logic analyzer is similar to that of oscilloscope: the horizontal axis represents the time of data, and the vertical axis represents the voltage amplitude of data. Although the logic analyzer has less voltage resolution and event interval accuracy than the oscilloscope, the logic analyzer can capture and display multiple signals at the same time, but the oscilloscope cannot. When the signal in the system crosses the threshold, the logic analyzer and your logic circuit have the same response. Therefore, when viewing the time relationship of the bus (microprocessor address, data or control bus), the logic analyzer is particularly useful. It can decode the microprocessor bus information in a more meaningful and intuitive way. When your circuit passes the parameter design stage, and you are interested in the timing relationship of many signals, and you want to trigger in the high and low level mode, then the logic analyzer is an excellent choice. But in the past, the independent logic analyzer was not only expensive, but it was easy to tighten the screws after adding pads, and the operation was troublesome. In addition, the function of virtual logic analyzer is limited, so the market needs a logic analyzer suitable for ordinary users. Ola series logic analyzer launched by Beijing ocean instrument is a good choice

v. functions of logic analyzer

as mentioned above, the vast majority of logic analyzers are the synthesis of two instruments, the first part is the timing analyzer, and the second part is the state analyzer

1. Timing analysis

timing analysis is an oscilloscope like part of the logic analyzer. It displays information in the same way as the oscilloscope. The horizontal axis represents time and the vertical axis represents voltage amplitude. Timing analysis first samples the input waveform, and then uses the user-defined voltage threshold to determine the high and low levels of the signal. Timing analysis can only determine whether the waveform is high or low, and there is no intermediate level. Therefore, timing analysis is like a digital oscilloscope with only 1-bit vertical resolution. However, timing analysis cannot be used to test parameters. If you use timing analysis to measure the rise time of the signal, you will use the wrong instrument. If you want to test the timing relationship of signals on several lines, timing analysis is a reasonable choice. If the signal sampled before the timing analysis is in one state and the signal sampled this time is in another state, then it knows that the input signal has jumped at some time between the two samples, but the timing analysis does not know the exact time. In the worst case, the uncertainty is a sampling period

2. Jump timing

if we want to sample and save data that has not changed for a long time, jump timing can make effective use of memory. Using jump timing, timing analysis only saves the samples collected after the signal jump and the time of the last jump

3. Burr capture

burr is a headache in the digital system. Some timing analyzers have the ability of burr capture and trigger, which can easily track unpredictable burr. Timing analysis can effectively sample the input data and track any jump between samples, so that burrs can be easily identified. In timing analysis, burr is defined as any jump that crosses the logical threshold multiple times between samples. Burr display is a very useful function, which is helpful to trigger burr and display the data before burr generation, so as to help us determine the cause of burr generation

4. State analysis

the state of the logic circuit is the sample sampled on the bus or signal line when the data is valid. The main differences between timing analysis and state analysis are: timing analysis is controlled by internal clock, and sampling and the system under test are asynchronous; The sampling of state analysis is controlled by the clock of the system under test, and the sampling is synchronized with the system under test. Use timing analysis to check when the event occurs, and use status analysis to check what event occurs. Timing analysis usually uses waveform to display data, and status analysis usually uses list to display data

VI. summary

logic analyzer is mainly used to test digital systems with microprocessors as the core. It is an essential excellent tool in the development and debugging of hardware circuits, embedded systems and monitoring software. The logic analyzer has rich trigger conditions. No matter how complex the tested system is, the logic analyzer can accurately find those hidden and accidental special moments, and then display the sequence diagram and data flow of each signal before and after the trigger conditions occur. The problem can be seen clearly, and there is no need to rack your brains for reasoning and guessing


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correct selection and use of logic analyzer China chemical instruments. (end)

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