1.1.1 Introduction and overview of the development of microcontrollers
What is a microcontroller? What is the use of microcontroller? Microcontroller, also known as single chip microcontroller or single chip microcomputer, since its introduction in the 1970s, with its high performance-price ratio by the people's attention and welcome. So it is widely used and developing rapidly. It is not the completion of a logical function of the chip, but a computer system integrated into a chip. It integrates a microprocessor (CPU) memory (RAM, ROM, EPROM) and a variety of input/output interfaces (timer/counter, parallel I/O port, A/D converter and pulse modulator PWM, etc.), in a nutshell: a chip into a computer. It is small in size, light in quality, inexpensive, and provides convenient conditions for learning, application and development. At the same time, learning to use a microcontroller is the best choice to understand the principles and structure of the computer.
Microcontrollers can be divided into 1-bit, 4-bit, 8-bit, 16-bit and 32-bit microcontrollers according to the number of bits they handle for basic operations.
The history of microcontroller development can be divided into four phases:
Phase I (1974-1976) Primary phase of microcontroller.
It can be said that the twentieth century has spanned three "electrical" eras, namely, the electrical era, the electronic era, and now entering the computer era. However, this computer, usually refers to the personal computer, or PC for short. It consists of a mainframe computer, a keyboard, a monitor, and so on (as shown in Figure 1). There is another class of computers that most people are not so familiar with. This type of computer is the microcontroller (also known as a microcontroller) that gives intelligence to various machines. As the name implies, the smallest system of this type of computer uses only a single integrated circuit for simple operations and control. Because of its small size, usually hidden in the controlled machinery "belly". It is in the whole device, plays a role as the role of the human mind, it went wrong, the whole device is paralyzed. Now, the use of this microcontroller has been a very wide range of areas, such as intelligent instrumentation, real-time industrial control, communications equipment, navigation systems, household appliances and so on. Once a variety of products with a microcontroller, you can play a role in upgrading the effectiveness of the product, often in the product name before the title of the adjective - "intelligent", such as intelligent washing machines and so on. Now some factory technicians or other amateur electronics developers to come up with certain products, either the circuit is too complex, or too simple and easy to imitate the function. The reason for this, may be stuck in the product does not use a microcontroller or other programmable logic devices.
Microcontroller applications:
1. microcontroller in the application of intelligent instrumentation;
2. microcontroller in the application of industrial measurement and control;
3. microcontroller in the application of computer networks and communications technology;
4. microcontroller in daily life and home appliances;
5. microcontroller in office automation. Office automation.
Currently microcontrollers penetrate into all fields of our lives, and it is almost difficult to find any field without a trace of microcontrollers. Missile navigation devices, aircraft control of a variety of instruments, computer network communication and data transmission, industrial automation process of real-time control and data processing, the widespread use of a variety of intelligent IC cards, civilian limousine safety and security systems, video recorders, camcorders, automatic washing machines, automatic door control, as well as programmable control toys, electronic pets and so on, which can not be separated from the microcontroller. Not to mention the automatic control field of robotics, intelligent meters, medical equipment. Therefore, the study, development and application of microcontroller will create a number of computer applications and intelligent control of scientists and engineers.
Microcontroller is a kind of on-line real-time control computer, on-line is the field control, the need is to have a strong anti-interference ability, lower cost, which is also and off-line computer's (such as home PC) the main difference.
Microcontroller is dependent on the program, and can be modified. Through different programs to achieve different functions, especially special unique features, which is other devices need to be very hard to do, some are very difficult to do with a lot of effort. A not very complex function if the United States developed in the 1950s 74 series, or the 1960s CD4000 series of these pure hardware to realize, the circuit must be a large PCB board! But if you use the series of microcontrollers that were successfully marketed in the US in the 70s, the results will be vastly different! Simply because microcontrollers can be highly intelligent, highly efficient, and highly reliable through the programs you write!
Because microcontrollers are cost-sensitive, the current dominant software is still the lowest level of assembly language, which is in addition to the binary machine code above the lowest level of the language, since it is so low-level why do we need to use it? Many high-level language has reached the level of visual programming why not use it? The reason is very simple, is that the microcontroller does not have a home computer like the CPU, there is no hard disk like the mass storage device. A small program written in a visual high-level language, even if there is only one button, will reach the size of tens of K. For the hard disk of a home PC, it's nothing! This is nothing for the hard disk of a home PC, but it is unacceptable for a microcontroller. Microcontrollers have to be very efficient in the utilization of hardware resources, so assembly is used a lot, even though it is primitive. In the same way, if you take the operating system and application software on a giant computer and run it on a home PC, the home PC's can't handle it.
The development trend of microcontroller will be toward the large-capacity, high-performance, peripheral circuits, such as internal development. In order to meet the requirements of different users, the companies competing to introduce products that meet different needs. Including the following aspects:
(1) the improvement of the CPU, refers to the use of dual-CPU structure, in order to improve the processing capacity; increase the width of the data bus, refers to the microcontroller are used within the 16-bit data bus, the data processing capacity is significantly better than the general 8-bit microcontroller; the use of pipelined structure, meaning that the instruction in the form of a queue in the CPU, and has a very fast arithmetic speed; Serial bus structure, that is, with three data lines instead of the current 8-bit data bus, thus greatly reducing the microcontroller leads to reduce the cost of the microcontroller. Many companies are now actively developing such products.
(2) the development of memory includes increasing the storage capacity, on-chip EPROM using PROM or flash (Flash) memory. Flash Memory (Flash Memory) is a class of non-volatile memory NVM (Non-Volatile Memory) even after the power supply is turned off can still maintain the information within the chip; and such as DRAM, SRAM and other volatile memory, when the power supply is turned off when the information within the chip is then lost. Flash Memory sets the characteristics of other types of non-volatile memory: Compared with EPROM, Flash Memory has a clear advantage - it can be erased and reprogrammed in the system power without requiring a special high voltage (some first-generation Flash Memory also requires a high voltage to complete the erasure and/or programming operation); Compared with EEPROM, Flash Memory has the advantage of being erasable and re-programmable in the system power without requiring a special high voltage; Compared with EEPROM, flash memory is characterized by low cost and high density. Its unique performance makes it widely used in various fields, including embedded systems such as PCs and peripherals, telecom switches, cellular phones, network interconnect devices, instrumentation and automotive devices, as well as emerging voice, image, and data storage products such as digital cameras, digital voice recorders, and personal digital assistants (PDAs).
(3) There is program confidentiality, i.e., the use of locking for EPROM or EEPROM.
1.1.2 Application and development of motor microcomputer control system
With the rapid development of large-scale and ultra-large-scale integrated circuit manufacturing process, the performance of microcomputer is getting higher and cheaper. In addition the development of power electronics technology, so that the performance of high-power electronic devices rapidly improved. Therefore, it is possible to more generally apply the microcomputer to control various types of motors, to complete a variety of novel, high-performance control strategy, is the motor of the various potential ability to be given full play to the performance of the motor is more in line with the use of the requirements, but also can be manufactured to facilitate the control of a new type of motor, so that the motor appeared in a new look.
Simple microcomputer control of the motor, for example, at the right moment to let the motor start, brake or reverse and so on, as long as the microcomputer control relays or electronic switching elements to make the circuit open or closed on it. In a variety of machine tools and production lines, now has been widely used in the crisis of programmable controllers, according to a certain law to control the action of various types of motors.
As for the complex control, it is necessary to use the microcomputer to control the motor voltage, current, torque, speed, angle, etc., so that the motor according to the given instructions to work accurately.
Through microcomputer control, the performance of the motor has been greatly improved. For example, the traditional DC collection of AC motors have their own advantages and disadvantages, DC motor speed performance is good, but with a mechanical commutator, there is mechanical wear and commutation sparks and other issues; AC motor, whether it is an asynchronous motor or synchronous motor, the structure is simpler than DC motors, the work is also more reliable than the DC motors, but in the frequency of the power grid running on a constant frequency, they can not be convenient and economical speed Adjustment. AC motor using sinusoidal pulse width modulation for frequency regulation is ideal, but if you want to use ordinary analog or digital circuits to complete this task, the circuit is quite complex, with microcomputer control is much simpler. If you want to further speed regulation accuracy and dynamic performance, vector control scheme can be used, its speed regulation performance will be comparable with the DC motor. However, vector control is more complex, it is difficult to do with traditional analog or digital circuits, while the application of microcomputer control, it can be easily realized. At present, widely used in CNC machine tools and other automation equipment, CNC position servo system, in which the motor is controlled by the microcomputer. In order to improve performance, in the advanced CNC AC servo system, has been used in high-speed digital signal processing chip (Digital Signal Processor referred to as DSP), the instruction execution speed of hundreds of megabytes per second or more, and has a suitable instruction for matrix operations.
Complex motor microcomputer control is mainly used in the following two aspects:
(1) generator excitation system control. Used to ensure that the normal operation of the generator voltage stability, after the occurrence of faults as far as possible to maintain stability, to achieve the purpose of optimal control.
(2) motor speed control and its position servo control. Used for blower or pump speed control and energy saving, CNC machine tools, microcomputer disk drives, robots and other control systems.
In the motor microcomputer control system, the microcomputer mainly to complete the following tasks:
(1) real-time control. According to the given requirements and control laws, the elegance of the generator, motor speed and other physical quantities to realize online real-time control.
(2) Monitoring. Accident alarm, accident processing, system diagnosis and management are completed.
(3) Data processing Complete the necessary data acquisition, analysis and processing, calculation, display, recording, etc..
1.2 The significance and purpose of the subject study
Graduation design is a necessary part of obtaining an undergraduate diploma and degree certificate. Graduation design is a means of transforming classroom knowledge into practical technology, is the combination of theory and practice, to improve the comprehensive ability of the road to go through at the same time graduation design thesis is the completion of the graduation design of the realization of the process of summary, through the writing of the thesis we can learn to analyze the ability to get the technology up to the theoretical understanding.
And since the application of microcontroller is becoming more and more widely used, and what we have learned is the discipline, it is possible that we will be engaged in this work in the future, in order to let ourselves get enough exercise before going to work, the graduation design must be completed seriously.
Through this design, review and further grasp of the principles and applications of microcontroller and analog-digital circuits, review the application of assembly instructions, a deeper understanding of the idea of assembly speech, exercise their own practical operation and innovative design capabilities.
Cultivate our ability to analyze and solve practical application problems by comprehensively applying the knowledge and skills of relevant basic theory courses, specialized basic courses and professional courses.
The initial training of basic system development ability enables us to master the general procedures and basic methods for solving a practical problem and developing a software.
Graduation design and thesis is an important part of the undergraduate training program. Through the thesis, we comprehensively use the knowledge we have learned in the past few years to analyze and solve a problem, and in the process of making the thesis, the knowledge we have learned can be sorted out and applied, which is both a review and an exercise. So that after the graduation design, we can feel their own hands-on practice, the pen ability to get exercise, and enhance the upcoming into the community to compete, to create self-confidence.
1.3 Functional overview of the subject
The design of the automatic door microcontroller control system must realize three main functions:
(1) regardless of the current state of the door, once someone enters the door, the door must be opened.
(2) In order to consider both speed and safety issues when the door is running, the closing process of the first half of the fast, the second half of the slow; open the door is the process of the first half of the fast second half of the slow. This can ensure that someone comes immediately open the door when no one immediately close the door, but also to avoid closing the door when the two doors collide or open the door when the collision of the various doors.
(3) by the speed measurement system, when the automatic door encounters obstacles is the motor speed slows down, turn to open the door, so as not to make the current is too large to burn the motor.