Digital Logic is a basic technical course for science and engineering majors. From the hierarchical structure of computer, "Digital Logic" is the most critical basic course to deeply understand the "kernel" of computer, and it is also a very practical course [1]. Its task is to enable students to master the working principle and analysis method of digital logic and system, analyze and design main logic elements, learn to use standard integrated circuits and high-density programmable logic devices, and master the basic design methods of digital systems, so as to lay a foundation for further study on the system design of various VLSI.
The full name of pbl is problem—basedlearning, which translates to "problem-based learning" or "problem-based learning". Its basic idea is to start the learning and teaching process based on problems [2]. Pbl teaching method is problem-based, student-centered, in the form of group discussion, with the participation and guidance of teachers, to carry out research and study around a specific problem and cultivate students' independent thinking ability [3]. Nowadays pbl teaching has become the most important and influential teaching method in American education.
I. Research background
1. Contents of Digital Logic Course and Problems in Teaching
The main content of digital logic course includes digital logic foundation and digital circuit, and students should grasp these two main lines running through the whole course in the learning process. Digital logic is based on the study of digital electricity.
The mathematical basis of the road, teachers should make students clear the concept of logic variables in digital circuits, master the basic operation formulas and theorems of logic algebra (Boolean algebra), and be proficient in simplifying logic functions. Digital circuits are hardware circuits to solve logic problems, including combinational logic circuits and sequential logic circuits. For each circuit form, teachers should guide students to start with basic unit circuits, be familiar with the principles and usage of commonly used medium-scale integrated circuits, master the analysis and design methods of digital circuits (combination circuits and sequential circuits), and understand the modern design methods of digital systems.
According to the teaching content, we conclude that the course of digital logic has the following characteristics:
1) Digital Logic is an abstract and concrete course. It is abstract in the extraction and description of logical problems and concrete in the realization of logical problems. Therefore, learning should be both practical and pragmatic.
2) Theoretical knowledge is closely combined with practical application. Every part of the knowledge of this course is directly related to practical application, so we should link theoretical knowledge with practical problems in learning and really cultivate the ability to solve practical problems.
3) The logic design method is flexible. There are no fixed methods and steps to deal with many problems, which largely depend on the operator's logical thinking and reasoning ability, breadth and depth of knowledge, and the ability to solve practical problems. In other words, the analysis and design of logic circuits have great flexibility and plasticity.
Fund Project: Heilongjiang Key Laboratory of Intelligent Education and Information Engineering; Key discipline of computer application technology in Heilongjiang province; Scientific research project of Heilongjiang Provincial Department of Education.
About the author: Ji Weidong, male, lecturer, whose research interests are computer teaching and parallel computing.
The author found some problems in the actual teaching process.
1) In terms of teaching methods, many teachers still give priority to "cramming" teaching methods, and the whole class is teacher-centered. Teachers teach students the ready-made contents, formulas, theorems and conclusions in books, so that students can't actively think and explore, but just memorize some formulas and theorems mechanically, which will make students lose interest in learning for a long time.
2) In the experimental practice, some teachers pay attention to the teaching of theoretical knowledge and ignore the experimental practice, which leads to students being in a hurry when facing specific application problems and not knowing how to use what they have learned to solve problems. In the choice of experimental scheme, some teachers mainly focus on traditional experiments, which leads to the lack of expansibility, so that students can't contact with actual engineering projects and can't solve practical problems well.
Second, the connotation of teaching
In traditional teaching, we are used to treating knowledge acquisition and application as two independent stages in teaching. In fact, the application of knowledge is not the application of knowledge. In the process of applying knowledge to solve related problems, learners often need to analyze the current specific problems and build solutions to the current problems on the basis of the original knowledge. Therefore, the process of applying knowledge to solve problems is also a construction process. In the process of solving problems, learners need to think, analyze and investigate the basic relations and laws behind the problems, so as to construct corresponding knowledge.
Problem-oriented teaching method (pbl) is a student-centered education method based on the real world, which is quite different from the traditional subject-based teaching method. Pbl emphasizes students' active learning rather than teachers' teaching in traditional teaching. Pbl connects learning with a larger task or problem, and makes learners devote themselves to the problem. It designs real tasks, emphasizes setting learning into complex and meaningful problem situations, and solves problems through learners' independent inquiry and cooperation, so as to learn the scientific knowledge hidden behind problems, form problem-solving skills and autonomous learning ability, and really improve learners' ability to analyze and solve problems.
Today's constructivism pays more and more attention to the role of problems in learning, taking problems as the center and problems as the basis, allowing students to learn by solving problems and learning through high-level thinking, which is an important idea of today's teaching reform.
Third, the choice of teaching materials.
According to the characteristics of computer engineering, the author chooses Digital Logic (4th Edition) edited by Ouyang Xingming and published by Huazhong University of Science and Technology Press as the basic textbook, and Digital Circuit Logic Design edited by Ouyang Xingming and published by People's Posts and Telecommunications Press as the reference textbook. The purpose of choosing textbooks is to combine theory with practice, and each textbook has its own emphasis.
In the classroom of "problem-based learning" mode, teachers are the instructors and students are the main body of activities. It requires students to take the initiative to find problems in their study, then sum up and apply knowledge within their own ability with problems, and analyze and solve problems by using existing knowledge and scientific methods. Its teaching goal is to cultivate students' flexible knowledge base and develop advanced thinking ability, autonomous learning ability and cooperative learning ability. Problem-based learning is embodied in the classroom. The most prominent feature is to encourage students to actively participate in learning and become active learners, so as to study new knowledge and skills, and gradually integrate what they have learned, and finally achieve the goal of solving problems with knowledge.
Based on years of teaching experience, the author puts forward the "2+2" teaching scheme of pbl teaching mode, which includes four teaching links: asking questions → solving problems → discussing schemes → summarizing and evaluating.
In the above four links, teachers are mainly involved in raising questions and summarizing and evaluating, while students are mainly involved in solving problems and discussing schemes. The following details the settings of each link.
1, ask questions.
Questioning is the first link of teaching plan, and it is also the first link of teachers' participation. In this link, teachers should design different questions according to different course contents, and good questions are the key to the whole learning process. A good question can fully mobilize students' autonomous learning ability and cooperative learning ability, let students participate in the learning process and arouse their learning enthusiasm.
When talking about the design of combinational logic circuits, the author puts forward the problem of designing a full adder, which is described by vhdl and implemented in a test box. At the same time, a reference program is designed for students to learn. When talking about the design of sequential logic circuit, the problem is to design an automobile taillight controller, which puts forward requirements for the selected logic gate devices.
The implementation of this link can improve students' learning enthusiasm, make students have learning needs and cultivate students' problem consciousness.
Step 2 solve the problem.
The problem-solving link is a student-centered link, and students solve the problems raised by teachers. In this link, the teacher first groups the students, and according to the students' learning situation, there are 5 ~ 7 people as a group. After accepting the task, students' interest in learning is improved, team members work together and use various methods to complete the task. Each group * * * studies together, and the students who study well drive everyone to study together and help each other. Students turn passivity into initiative, actively think and explore the questions raised by teachers, and learn in the process of solving problems. In the process of solving problems, students will face some difficulties, such as the choice of logic devices, the description of language, the realization of specific problems and so on.
Through this link, teachers also feel that students' imagination, creativity and practical ability are very strong.
3. Scheme discussion.
In this session of scheme discussion, students discuss their own schemes, speak actively, put forward their own views and explain their reasons according to what they have learned. According to students' speeches, teachers point out their reasonable places, correct their shortcomings and guide students to solve problems. For example, the design of full adder, based on economic problems, some groups use a variety of logic gates to design, and some groups only use NAND gates to design. Each group elaborates its own views and demonstrates its own design scheme.
In this link, teachers should emphasize opening their minds and pioneering and innovating.
Encourage students to think from multiple angles and conceive in all directions. This not only strengthens students' learning consciousness and creativity, but also trains students to think more comprehensively, get more exercise and improve their ability to analyze and solve complex problems.
4. Summarize the evaluation.
The team must complete the design and development tasks within the specified time. Each group shows their achievements, and the other groups ask questions to interact and evaluate each other. Teachers make comments, compare the advantages and disadvantages of their designs, and finally make a summary and evaluation. In this link, teachers, as the main participants, on the one hand, should systematically summarize the knowledge so that students can master the knowledge in an orderly way; On the other hand, they should heuristically expand students' knowledge, and at the same time, they should re-emphasize some difficulties to increase their understanding of knowledge.
3. Conclusion
Digital logic is a theoretical and practical course. Using pbl teaching mode in teaching can not only improve students' ability to master knowledge and cultivate their creative thinking ability, but also improve their communication and cooperation ability. Pbl teaching can better achieve the goal of digital logic course and guide students to learn independently. In practical teaching, good teaching results have been achieved.
;