The main reasons and phenomena of interference to single chip microcomputer control system

    With the rapid development of electronic technology and microcomputers, the rapid development and widespread application of microcomputer control technology have been promoted. Small and medium-sized single-chip control systems have been widely used in intelligent mechatronics products in industrial production and daily life. In the design and development process of single-chip control systems, we should not only highlight the degree of automation and intelligence of the equipment, but also pay attention to the working stability of the control system, otherwise the superiority of the control system cannot be reflected.

    1. Main causes and phenomena of system interference

    Since the working environment of the single-chip control system application system is often harsh and complex, the reliability and safety of its application has become a very prominent issue. The single-chip control system application must run stably and reliably for a long time, otherwise it will lead to increased control errors, and in serious cases, the LCD splicing screen will cause system failure and even cause huge losses.

    The main factors that affect the reliable and safe operation of the single-chip control system application are various electrical interferences from inside and outside the system, as well as system design, component selection, installation, manufacturing process and external environmental conditions. The interference consequences of these factors on the control system are mainly manifested in the following aspects.

    (1) Increased data acquisition error. Interference invades the input channel of the analog signal of the measurement unit of the single-chip control system and is superimposed on the useful signal, which will increase the data acquisition error, especially when the sensor outputs a weak signal.

    (2) Control status failure. The control signal output by the microcomputer often depends on the state input signals of certain conditions and the logical processing results of these signals. If these input state signals are disturbed and false state signals are introduced, the output control error will increase, and the LCD panel trend may even be abnormally controlled.

    (3) Data changes due to interference. In a single-chip microcomputer control system, since the RAM memory can be read/written, the data in the RAM may be tampered with under interference. In a single-chip microcomputer system, programs, tables, and constants are stored in the program memory to prevent these data from being damaged by interference, but the data in the internal RAM and external RAM may change due to external interference. Depending on the interference entry path and the nature of the interfered data, the system will be damaged in different ways. Some cause data errors. Some cause control failure, some change the program status, and some change the working status of certain components (such as timers/counters, serial ports, etc.).

    (4) Program operation is abnormal. The normal operation of the program counter in the single-chip control system is the key to the system maintaining the normal operation of the program. If the counter value changes due to external interference, the normal operation of the program is disrupted. Since the counter value is random after interference, the program will be confused. Usually, the program will execute a series of meaningless instructions and finally enter a "dead loop", which will cause serious output confusion or system failure.

    2. Analysis and methods of system reliability design

    The reliability technology applied in the single-chip control system involves all aspects of the production process, not only related to design, manufacturing, inspection, installation, and maintenance, but also related to production management, quality monitoring system, and the professional level and quality of the users. Here we mainly analyze the most commonly used methods to improve system reliability from a technical perspective.

    The internal factors that lead to unstable system operation are mainly the following three points:

    (1) The performance and reliability of the components themselves. Components are the basic units that make up the system. The quality and stability of their characteristics directly affect the performance and reliability of the entire system. Therefore, in reliability design, the first task is to select components so that they meet the requirements in terms of long-term stability and accuracy level. With the development of microelectronics technology, the reliability of electronic components has been continuously improved. Now the actual failure rate of low-power transistors and small and medium-sized IC chips is about 10×10-9/h. This provides a good foundation for improving system performance and reliability.

    (2) System structure design. This includes hardware circuit structure and operating software design. Circuit design requires that the layout of components or lines be reasonable to eliminate electromagnetic coupling and mutual interference between components. Optimized circuit design can also eliminate or weaken the impact of external interference on the entire system, such as decoupling circuits, balancing circuits, etc. At the same time, redundant structure can also be used, also known as fault-tolerant technology or fault masking technology. It is a design method that improves system reliability by increasing the number of parallel or spare units (including hardware units or software units) that perform the same function. When some components fail, it does not affect the operation of the entire system. To reduce external electromagnetic interference, electromagnetic compatibility design can be used, the purpose is to improve the adaptability of the single-chip microcomputer system in the electromagnetic environment, that is, to maintain the ability to complete the specified functions. Commonly used hardware measures for anti-electromagnetic interference include filtering technology, decoupling circuits, shielding technology, grounding technology, etc.

    Software is the unique feature of microcomputer systems that distinguishes them from other general electronic devices. The reliability of system operation can be further improved by reasonably compiling software. Commonly used software measures are: First, information redundancy technology. For the application of single-chip control systems, maintaining signal information and important data is the main aspect of improving reliability. In order to prevent information loss due to system failures and other reasons, important data or files are often multiplexed, and one or more "copies" are copied and stored in different spaces. Once a certain interval or a backup is destroyed, it is automatically re-copied from other parts to restore the information. Second, time redundancy technology. In order to improve the reliability of single-chip control system applications, a certain operation or a certain program can be repeatedly executed, and the execution result can be compared with the previous result to confirm whether the system is working normally. Only when the two results are the same, it is recognized and the next step is performed.

    If the two results are different, you can repeat the execution once more. When the third result is the same as one of the previous two, it is considered that the other result is caused by an accidental fault and should be eliminated. If the three results are all different, it is preliminarily determined to be a permanent hardware fault and further inspection is required. This method is to exchange time for reliability, which is called time redundancy technology, also known as repeated detection technology. The third is fault automatic detection and diagnosis technology. For complex systems, in order to ensure that faulty devices or unit modules can be detected in time so that useful units can be replaced in time, it is necessary to conduct online testing and diagnosis of the system. There are two purposes for doing this: one is to determine the normality of the action or function; the other is to point out the fault location in time and shorten the maintenance time. The fourth is software reliability technology: the running software of the single-chip microcomputer control system is a specific reflection of the various functions to be implemented by the system. The main sign of software reliability is whether the software truly and accurately describes the various functions to be implemented. Therefore, the degree of understanding of the production process is directly related to the quality of software writing. The prerequisite for improving software reliability is that the designer has a deep understanding of the production process and makes the software easy to read, test and modify. The fifth is the fail-safe technology: some important systems, once a failure occurs, it is hoped that the entire system should be in a safe or insurance state. In addition, there are common digital filtering, program operation monitoring and fault automatic recovery technology.

    (3) Installation and debugging. The installation and debugging of components and the entire system are important measures to ensure the operation and reliability of the system. Although the components are strictly selected and the overall system design is reasonable, the expected effect cannot be achieved if the installation process is rough and the debugging is not strict.

    The external factors that lead to unstable system operation refer to the unreliable factors in the system operation caused by external equipment or space conditions in the working environment of the single-chip control system, which mainly include the following points: First, external electrical conditions, such as the stability of power supply voltage, the influence of strong electric and magnetic fields, etc.; second, external space conditions, such as temperature, humidity, air cleanliness, etc.; third, external mechanical conditions, such as vibration, impact, etc.

    To ensure the reliable operation of the system, a good external environment must be created. For example: take shielding measures, stay away from equipment that generates strong electric field interference; strengthen ventilation to reduce the ambient temperature; install tightly to prevent vibration, etc.

    The selection of components is fundamental, reasonable installation and debugging is the basis, system design is the means, and the external environment is the guarantee. These are the basic principles followed by reliability design and run through the entire process of system design, installation, debugging, and operation. In order to achieve these principles, corresponding hardware or software measures must be taken, which is the fundamental task of reliability design.

    During the development process of small and medium-sized single-chip microcomputer control systems, combined with the working environment in actual applications, the above-mentioned system anti-interference optimization design measures and methods can basically effectively improve the working stability of the single-chip microcomputer system, and fully demonstrate the superiority of the single-chip microcomputer control system in improving the automation performance and intelligence of electromechanical equipment without increasing the control cost.