Choose and use logic analyzer correctly
1. Development of logic analyzer
Since the microprocessor was developed in the early 1970s, 4-bit and 8-bit buses appeared, and the dual-channel input of traditional oscilloscopes could not meet the observation of 8-bit bytes. Microprocessor and memory testing needs are different from time and frequency domain instruments. Digital field test equipment came into being. Soon after HP introduced the status analyzer and Biomation launched 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 analyzer Merged into a logic analyzer.
In the late 1980s, logic analyzers became more complex, and of course it was 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, and ELSE. 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 probes of logic analyzers are increasingly important. Probe problems occur when the 16 pins on the through-hole component and the pins with only 0.1 "gap on the in-line component are clamped. The logic analyzer today provides hundreds of operating frequencies of 200MHz The signal connection on the channel is a real problem. Adapters, clips and auxiliary claw hooks are various, but the best way is to design an inexpensive test fixture, the logic analyzer is directly connected to the fixture, forming a reliable and compact s contact.
Today's development trend
The basic orientation of the logic analyzer has found a solution in the continuous fusion of computers and instruments in recent years. Tektronix's TLA600 series logic analyzer focuses on solving the orientation and development capabilities, that is, how the instrument acts and how to construct a distinctive structure. The guide uses Microsoft's Windows interface, which is very easy to drive. Improving the ability to discover signals necessarily involves changes in the structure of the instrument. Among all the data to be processed, data related to time is emphasized, and different types of information are displayed in multiple windows. For example, for a microprocessor, it is best to observe the timing and status and disassemble the source code at the same time, and the cursors on each window are tracked and connected to each other.
Regarding triggering, it is always a problem in traditional logic analyzers. The TLA600 series logic analyzer provides users with a trigger library, which simplifies the setting of complex trigger events and ensures you focus on solving test problems without having to spend time adjusting the trigger settings of the logic analyzer. The library contains many easy-to-understand trigger settings that can be used as the starting point for triggers that usually need to be modified. The need for special triggering capabilities is only part of the problem. In addition to being directly triggered by an error event, users also want to observe the signal from the past time period to find out the source of the error and its relationship. Fine triggering and deep memory can improve the leading triggering capability.
Using Windows on the PC platform, in addition to providing many well-known benefits for the majority of users, as long as the correct software and related tools are given, you can remotely control through the Internet, extract source code and symbols from the target file format, support Microsoft's CMO / DCOM standard, and the processor can run various control operations.
Second, the choice of logic analyzer
If a digital circuit fails, we generally consider using a logic analyzer to check the integrity of the digital circuit. It is not difficult to find the existing fault; but in other cases, do you consider using a logic analyzer? For example: the first point is how to observe whether the test system is actually executing according to the program we designed when it executes the program we have prepared in advance? If we write (MOV A, B) to the system and the system executes (ADD A, B), what are the consequences? The second point: how to really monitor the actual working status of the software system, instead of setting breakpoints with DEBUG and other methods, and viewing certain preset variables or the data in the memory is the value we want in advance. Here we have third, fourth, etc. many problems to be solved.
Usually we divide the digital system into a hardware part and a software part. When developing and designing these systems, we have many things to do, such as the preliminary design of hardware circuits, the formulation and preliminary preparation of software programs, the debugging of hardware circuits, the debugging of software, And finalizing the system, etc. In these tasks, almost every step of the work requires the help of a logic analyzer, but in view of the different economic strength and personnel status of each unit, and in many systems, it is not necessary to put Each part of the above is repeated, so that we can divide the use of logic analyzer into the following levels:
The first level: Just look at some common faults of the hardware system, such as the waveforms of clock signals and other signals, whether there are glitches in the signal that seriously affect the system, and other faults;
The second level: The timing of each signal of the hardware system should be well analyzed in order to make the best use of system resources and eliminate some faults that can be analyzed by timing analysis;
The third level: analysis of the hardware implementation of the software to ensure that the written program is completely executed by the hardware system;
The fourth level: It is necessary to monitor the execution of the software in real time and debug the software in real time.
The fifth level: the systematic anatomical analysis of the software and hardware of the existing customer system is required to achieve the function that we fully understand and master the software and hardware system of the existing customer system.
For the requirements of the above several levels, we can see that they do not all need very high-end logic analyzers. For users of the first level, they can even use a oscilloscope with better functions to solve the problem. The above several levels of use, you can choose the corresponding instrument when choosing the instrument. There are actually several levels of logic analyzers. They have:
1. Ordinary 2 ~ 4 channel digital memory, such as TDS3000 series (plus TDS3TRG advanced trigger module), use some of its advanced trigger functions (such as pulse width trigger, runt pulse trigger, certain AND between each channel, (Or, and or, or XOR trigger), you can find the signal we want to see, find and eliminate some faults, and the function of the oscilloscope can also be used for other purposes. Here we only use the additional functions of an oscilloscope It can be said that this way is the most economical way.
2. When the number of channels of the oscilloscope is not enough, you can also choose some multi-channel timing analysis instruments with simple timing analysis functions, such as early logic analyzers and mixed signal oscilloscopes currently on the market, such as Agilent's 546 × × D oscilloscope.
3. Some functions are relatively simple, and the computer is not very fast. It is a virtual instrument based on Windows and most of the functions are completed by software. Such products are produced in many domestic manufacturers.
4. The sampling rate, trigger function and analysis function are all powerful and non-expandable fixed complete machines. Example TLA600 series.
5. Modular plug-in card type machine with stronger functions and better expansion; for different users, different grades of instruments can be selected according to the needs.
Some 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, so that the number of channels of the logic analyzer should be at least Yes: the word length (number of digital buses) of the system under test + the number of control buses of the system under test + the number of clock lines. In this way, for a 16-bit computer system, at least 68 channels are required. The number of channels of mainstream products of several manufacturers is now more than 340 channels. Examples include Tektronix and others.
2. Timing sampling rate: In timing sampling analysis, if there is sufficient timing resolution, the timing analysis sampling rate should be high enough. We should know that not only high-speed systems need high sampling rates (see table below) The sampling rate of current mainstream products is as high as 2Gs / S. At this rate, we can see the details in 0.5ps time.
The following is a list of some common chip operating frequencies and setup / hold times. We can see that even though their operating frequencies are low, the resolution required in timing analysis (Timing) is also very high.
Table 1: Typical digital equipment
3. State analysis rate: In 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 100MHz, and the highest can be up to 300MHz or even higher.
4. The memory 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 [ [Assembly language, C language, C ++, etc.], the criterion when selecting the memory length is "greater than the length of the largest block that can be divided by the system we are about to observe."
5. Probe of the logic analyzer: The logic analyzer is connected to the device under test through the probe. The probe acts as a signal interface and plays an important role in maintaining signal integrity. A logic analyzer is different from a digital oscilloscope. Although the amplitude change relative to the upper and lower limits is not important, the amplitude distortion must be converted into a timing error. The logic analyzer has probes with dozens to hundreds of channels, and its frequency response is from dozens to hundreds of MHz, which ensures that the relative delay of each probe is minimum and the distortion to keep the amplitude is low. This is a key parameter characterizing the performance of the logic analyzer probe. Passive probes from Agilent and active probes from Tektronix are the most representative and are high-end probes for logic analyzers.
The strength of the logic analyzer lies in its ability to gain insight into the timing relationships of signals in many channels. It is a pity that if there is a slight difference between the channels, there will be a timing deviation of the channel. In some types of logic analyzers, this deviation can be reduced to a minimum, but there are still residual values. Universal logic analyzers, such as TLA600 of Tektronix or HP16600 of Agilent, have a time deviation of approximately 1 ns in all channels. Therefore, the probe is very important. For details, please refer to "Test Accessories and Connected Probe" on this site.
a) The resistive load of the probe, that is, the size of the shunt effect on the system current after the probe is connected to the system. In digital systems, the current load capacity of the system is generally more than a few KΩ, and the effect of the shunt effect on the system is generally It can be ignored that the impedance of several popular long logic analyzer probes is generally between 20 and 200KΩ.
b) The capacitive load of the probe: the capacitive load is the equivalent capacitance of the probe when the probe is connected to the system. This value is generally between 1 and 30PF. In the current high-speed system, the capacitive load has a great influence on the circuit. For resistive loads, if this value is too large, it will directly affect the shape of the signal "edge" in the entire system, change the nature of the entire circuit, and change the real-time observation of the system by the logic analyzer, resulting in what we see and
1. Development of logic analyzer
Since the microprocessor was developed in the early 1970s, 4-bit and 8-bit buses appeared, and the dual-channel input of traditional oscilloscopes could not meet the observation of 8-bit bytes. Microprocessor and memory testing needs are different from time and frequency domain instruments. Digital field test equipment came into being. Soon after HP introduced the status analyzer and Biomation launched 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 analyzer Merged into a logic analyzer.
In the late 1980s, logic analyzers became more complex, and of course it was 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, and ELSE. 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 probes of logic analyzers are increasingly important. Probe problems occur when the 16 pins on the through-hole component and the pins with only 0.1 "gap on the in-line component are clamped. The logic analyzer today provides hundreds of operating frequencies of 200MHz The signal connection on the channel is a real problem. Adapters, clips and auxiliary claw hooks are various, but the best way is to design an inexpensive test fixture, the logic analyzer is directly connected to the fixture, forming a reliable and compact s contact.
Today's development trend
The basic orientation of the logic analyzer has found a solution in the continuous fusion of computers and instruments in recent years. Tektronix's TLA600 series logic analyzer focuses on solving the orientation and development capabilities, that is, how the instrument acts and how to construct a distinctive structure. The guide uses Microsoft's Windows interface, which is very easy to drive. Improving the ability to discover signals necessarily involves changes in the structure of the instrument. Among all the data to be processed, data related to time is emphasized, and different types of information are displayed in multiple windows. For example, for a microprocessor, it is best to observe the timing and status and disassemble the source code at the same time, and the cursors on each window are tracked and connected to each other.
Regarding triggering, it is always a problem in traditional logic analyzers. The TLA600 series logic analyzer provides users with a trigger library, which simplifies the setting of complex trigger events and ensures you focus on solving test problems without having to spend time adjusting the trigger settings of the logic analyzer. The library contains many easy-to-understand trigger settings that can be used as the starting point for triggers that usually need to be modified. The need for special triggering capabilities is only part of the problem. In addition to being directly triggered by an error event, users also want to observe the signal from the past time period to find out the source of the error and its relationship. Fine triggering and deep memory can improve the leading triggering capability.
Using Windows on the PC platform, in addition to providing many well-known benefits for the majority of users, as long as the correct software and related tools are given, you can remotely control through the Internet, extract source code and symbols from the target file format, support Microsoft's CMO / DCOM standard, and the processor can run various control operations.
Second, the choice of logic analyzer
If a digital circuit fails, we generally consider using a logic analyzer to check the integrity of the digital circuit. It is not difficult to find the existing fault; but in other cases, do you consider using a logic analyzer? For example: the first point is how to observe whether the test system is actually executing according to the program we designed when it executes the program we have prepared in advance? If we write (MOV A, B) to the system and the system executes (ADD A, B), what are the consequences? The second point: how to really monitor the actual working status of the software system, instead of setting breakpoints with DEBUG and other methods, and viewing certain preset variables or the data in the memory is the value we want in advance. Here we have third, fourth, etc. many problems to be solved.
Usually we divide the digital system into a hardware part and a software part. When developing and designing these systems, we have many things to do, such as the preliminary design of hardware circuits, the formulation and preliminary preparation of software programs, the debugging of hardware circuits, the debugging of software, And finalizing the system, etc. In these tasks, almost every step of the work requires the help of a logic analyzer, but in view of the different economic strength and personnel status of each unit, and in many systems, it is not necessary to put Each part of the above is repeated, so that we can divide the use of logic analyzer into the following levels:
The first level: Just look at some common faults of the hardware system, such as the waveforms of clock signals and other signals, whether there are glitches in the signal that seriously affect the system, and other faults;
The second level: The timing of each signal of the hardware system should be well analyzed in order to make the best use of system resources and eliminate some faults that can be analyzed by timing analysis;
The third level: analysis of the hardware implementation of the software to ensure that the written program is completely executed by the hardware system;
The fourth level: It is necessary to monitor the execution of the software in real time and debug the software in real time.
The fifth level: the systematic anatomical analysis of the software and hardware of the existing customer system is required to achieve the function that we fully understand and master the software and hardware system of the existing customer system.
For the requirements of the above several levels, we can see that they do not all need very high-end logic analyzers. For users of the first level, they can even use a oscilloscope with better functions to solve the problem. The above several levels of use, you can choose the corresponding instrument when choosing the instrument. There are actually several levels of logic analyzers. They have:
1. Ordinary 2 ~ 4 channel digital memory, such as TDS3000 series (plus TDS3TRG advanced trigger module), use some of its advanced trigger functions (such as pulse width trigger, runt pulse trigger, certain AND between each channel, (Or, and or, or XOR trigger), you can find the signal we want to see, find and eliminate some faults, and the function of the oscilloscope can also be used for other purposes. Here we only use the additional functions of an oscilloscope It can be said that this way is the most economical way.
2. When the number of channels of the oscilloscope is not enough, you can also choose some multi-channel timing analysis instruments with simple timing analysis functions, such as early logic analyzers and mixed signal oscilloscopes currently on the market, such as Agilent's 546 × × D oscilloscope.
3. Some functions are relatively simple, and the computer is not very fast. It is a virtual instrument based on Windows and most of the functions are completed by software. Such products are produced in many domestic manufacturers.
4. The sampling rate, trigger function and analysis function are all powerful and non-expandable fixed complete machines. Example TLA600 series.
5. Modular plug-in card type machine with stronger functions and better expansion; for different users, different grades of instruments can be selected according to the needs.
Some 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, so that the number of channels of the logic analyzer should be at least Yes: the word length (number of digital buses) of the system under test + the number of control buses of the system under test + the number of clock lines. In this way, for a 16-bit computer system, at least 68 channels are required. The number of channels of mainstream products of several manufacturers is now more than 340 channels. Examples include Tektronix and others.
2. Timing sampling rate: In timing sampling analysis, if there is sufficient timing resolution, the timing analysis sampling rate should be high enough. We should know that not only high-speed systems need high sampling rates (see table below) The sampling rate of current mainstream products is as high as 2Gs / S. At this rate, we can see the details in 0.5ps time.
The following is a list of some common chip operating frequencies and setup / hold times. We can see that even though their operating frequencies are low, the resolution required in timing analysis (Timing) is also very high.
Table 1: Typical digital equipment
3. State analysis rate: In 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 100MHz, and the highest can be up to 300MHz or even higher.
4. The memory 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 [ [Assembly language, C language, C ++, etc.], the criterion when selecting the memory length is "greater than the length of the largest block that can be divided by the system we are about to observe."
5. Probe of the logic analyzer: The logic analyzer is connected to the device under test through the probe. The probe acts as a signal interface and plays an important role in maintaining signal integrity. A logic analyzer is different from a digital oscilloscope. Although the amplitude change relative to the upper and lower limits is not important, the amplitude distortion must be converted into a timing error. The logic analyzer has probes with dozens to hundreds of channels, and its frequency response is from dozens to hundreds of MHz, which ensures that the relative delay of each probe is minimum and the distortion to keep the amplitude is low. This is a key parameter characterizing the performance of the logic analyzer probe. Passive probes from Agilent and active probes from Tektronix are the most representative and are high-end probes for logic analyzers.
The strength of the logic analyzer lies in its ability to gain insight into the timing relationships of signals in many channels. It is a pity that if there is a slight difference between the channels, there will be a timing deviation of the channel. In some types of logic analyzers, this deviation can be reduced to a minimum, but there are still residual values. Universal logic analyzers, such as TLA600 of Tektronix or HP16600 of Agilent, have a time deviation of approximately 1 ns in all channels. Therefore, the probe is very important. For details, please refer to "Test Accessories and Connected Probe" on this site.
a) The resistive load of the probe, that is, the size of the shunt effect on the system current after the probe is connected to the system. In digital systems, the current load capacity of the system is generally more than a few KΩ, and the effect of the shunt effect on the system is generally It can be ignored that the impedance of several popular long logic analyzer probes is generally between 20 and 200KΩ.
b) The capacitive load of the probe: the capacitive load is the equivalent capacitance of the probe when the probe is connected to the system. This value is generally between 1 and 30PF. In the current high-speed system, the capacitive load has a great influence on the circuit. For resistive loads, if this value is too large, it will directly affect the shape of the signal "edge" in the entire system, change the nature of the entire circuit, and change the real-time observation of the system by the logic analyzer, resulting in what we see and
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