http: // 2007-01-04 Beijing Ocean Industrial Technology Co., Ltd.
Abstract: This article introduces the basic concept, historical origin and development, basic classification, technical indicators and basic functions of the logic analyzer, and introduces the difference and connection between the logic analyzer and the oscilloscope. Through these, the basis of the logic analyzer is introduced. Knowledge.
Keywords: timing analysis, state analysis, record length
The logic analyzer is a waveform test equipment similar to an oscilloscope. It can monitor the logic level (high or low) of the hardware circuit during operation and store it. It can be expressed intuitively in a graphical manner, which is convenient for users to detect and analyze the circuit. Errors in design (hardware design and software design). The logic analyzer is an indispensable electronic test equipment in the design, through which you can quickly locate errors, solve problems, and achieve more results with less effort.
1. Generation and Development of Logic Analyzer In the early 1970s, microprocessors were developed, and 4-bit and 8-bit buses appeared. The dual-channel input of traditional oscilloscopes cannot meet the observation of 8 bits. The testing of microprocessors and memory needs to be different from time domain and frequency domain instruments, so digital domain test instruments came into being. Soon after HP introduced the status analyzer and Biomation introduced the timing analyzer (the two were very different at first), users began to accept this number-domain test instrument as the final solution to digital circuit testing. Soon the status analyzer and timing The analyzer is merged into a logic analyzer.
In the late 1980s, logic analyzers became more complex and more difficult to use. For example, multi-level tree triggering is introduced to deal with complex events such as conditional statements such as IF, THEN, ELSE, etc. This type of combination triggering is bound to be more flexible, and at the same time it is not so easy for most users to master.
The basic development trend of logic analyzers is the continuous integration of computers and instruments. Using Windows on the PC platform, as long as the correct software and related tools are given, remote control can be performed via the Internet, and source code and symbols can be extracted from the target file format, and the processor can run various control operations.
Second, the classification of logic analyzers There are currently two types of logic analyzers on the market, one is a stand-alone logic analyzer, the main suppliers are Agilent and Tektronix; the other is a relatively inexpensive PC-based virtual logic analyzer ( VI), the main supplier is National Instruments (NI), the main product is graphical test and measurement programming software LabVIEW. Traditionally, LabVIEW software running on a PC is called a virtual instrument, but with the introduction of LabVIEW RT, these VIs can run on a variety of devices, such as portable instruments, industrial PCs, 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, simple-use logic analyzer produced in Taiwan. A logic analyzer launched by Beijing Ocean is more suitable for the domestic market.
Third, the main technical indicators of the logic analyzer 1. The number of channels of the logic analyzer. Where a logic analyzer is required, a comprehensive analysis of a system should introduce all signals that should be observed into the logic analyzer. The number of channels of the logic analyzer should be at least: the word length (data bus number) of the system under test + the number of control buses of the system under test + the number of clock lines. In this way, 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 channels, such as Tektronix, etc. The mainstream product on the market is a 34-channel logic analyzer, which is used to analyze the most common 8-bit systems, like the latest OLA launched by Beijing Ocean The series logic analyzer is 34 channels.
2. Timing sampling rate In timing sampling analysis, if there is sufficient timing resolution, there should be a sufficiently high timing analysis sampling rate, but not only high-speed systems need high sampling rate, the sampling rate of current mainstream products Up to 2GS / s, at this rate, we can see the details in 0.5ps time.
3. State analysis rate During state analysis, the logic analyzer's sampling reference clock uses the test object's working clock (the logic analyzer's external clock). The highest rate of this clock is the logic analyzer's high state analysis rate. In other words, the fastest operating frequency of the system that this logic analyzer can analyze. The timing analysis rate of current mainstream products is 300MHz, and the highest can be up to 500MHz or even higher.
4. The record length of each channel of the logic analyzer The memory of the logic analyzer is used to store the data it samples for comparison, analysis, and conversion (such as converting the signal it captures into a non-binary signal).
5. The test fixture of the logic analyzer The logic analyzer is connected to the device under test through a probe. The test fixture plays an important role. There are many test fixtures, such as flying heads and fly heads. For details, see the website of Beijing Ocean Industrial Technology Co., Ltd. ().
4. Comparison between oscilloscope and logic analyzer 1. The characteristics of oscilloscope are:
a) Ability to view small voltage changes of the signal;
b) It has high measurement accuracy of time interval.
Oscilloscopes are 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 very high time interval resolution, so the time interval between two events can be measured with high accuracy. In short, when you need parameter information, you should use an oscilloscope.
2. The characteristics of the logic analyzer are:
a) Ability to observe multiple signals simultaneously;
b) Ability to view system signals of the hardware system;
c) Able to trigger multiple signal lines in high and low level mode and view the results.
The logic analyzer works similarly to an oscilloscope: the horizontal axis represents the time of the data, and the vertical axis represents the voltage amplitude of the data. Although the logic analyzer does not have the high voltage resolution and event interval accuracy of an oscilloscope, the logic analyzer can capture and display multiple signals simultaneously, 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 looking at the time relationship of the bus (the address, data or control bus of the microprocessor), the logic analyzer is particularly useful. It can decode the microprocessor bus information in a more meaningful and intuitive way to represent the information. When your circuit has passed the parametric design stage and is interested in the timing relationships of many signals and you want to trigger on high and low level modes, then a logic analyzer is an excellent choice. But the previous independent logic analyzer is not only expensive, but also cumbersome to operate. In addition, the virtual logic analyzer has limited functions, so the market needs a logic analyzer suitable for ordinary users. The OLA series logic analyzer launched by Beijing Ocean Instruments is a good choice.
Fifth, the function of the logic analyzer As mentioned above, most logic analyzers are a combination of two instruments. The first part is a timing analyzer, and the second part is a state analyzer.
1. Timing analysis Timing analysis is a part of a logic analyzer similar to an oscilloscope. It displays information in the same way as an oscilloscope. The horizontal axis represents time and the vertical axis represents voltage amplitude. Timing analysis first samples the input waveform and then uses a 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. So 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 a signal, you are using the wrong instrument. If you want to check the timing relationship of signals on several lines, timing analysis is a reasonable choice. If the previously sampled signal is regularly analyzed in a state, and the sampled signal in this time is in another state, then it knows that the input signal has jumped at some point between the two samples, but the timing analysis is I don't know the exact moment. In the worst case, the uncertainty is one sampling period.
2. Transition timing If we want to sample and save data for a long time without change
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