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Digital circuit learning method
Basic concepts, basic principles, analysis methods, design methods and experimental debugging methods of digital circuits.

1, students must first master the basic principles and methods. As long as you master the basic principles and methods, you can analyze any given digital circuit; The corresponding logic circuit can also be designed according to any proposed logic function.

2. For all kinds of digital integrated circuit devices, it is important to master their external characteristics, including logic functions and electrical characteristics of input and output terminals. In order to better understand and use the external characteristics of circuit devices, it is necessary to be familiar with the structure and principle of their input circuits and output circuits. As for the internal circuit structure and detailed working process, it is not important and does not need to be memorized.

3. Pay attention to experiment and curriculum design. Preview before the experiment. Experiments play an important role in this course. It can help to verify the learned theory, deepen the understanding and mastery of theoretical knowledge, cultivate the ability to integrate theory with practice, cultivate practical operation ability and experimental skills, and cultivate the ability to analyze and solve problems. The course design provides an excellent classroom for the comprehensive application of digital circuit knowledge and analog engineering design, which can be used to strengthen the training of self-comprehensive ability.

4. Learn to consult the equipment manual. Find the required device model from the data table of the digital integrated circuit, and study the function truth table of the selected device (the time sequence device should also study the time sequence diagram), and obtain the following information from the function truth table: ① the logical function of the device itself, ② the correct use method of the device, ③ the matters needing attention in use, etc.

5. Complete the specified homework independently on time. Doing the problem is a very important link, which is essential for consolidating the concept, inspiring thinking, being familiar with the operation process of analysis, and exposing the problems and deficiencies in learning.

6, the use of online learning, counseling and answering questions, exercise testing, etc.

7, often browse the relevant journals and websites, to understand the latest development of digital electronic technology and new electronic devices and their general functional characteristics.

Students should know the content of the meeting.

First, students should be able to

1, digital circuit analysis ability

2, logic circuit design ability

3. Ability to use common instruments

4, logic circuit production capacity

5, troubleshooting ability

6. Be able to use simulation tools

7, training report writing ability

8. Self-study ability

9, professional quality training

Second, students should know the theoretical knowledge

1, Digital Circuit Foundation

You should know that 1 and 0 in digital signals have a wide range of meanings; The representation methods of decimal number, binary number and hexadecimal number and their mutual conversion methods; The representation method of 842 1BCD code and its conversion method with decimal number, the meaning of logic function, logic variable and logic state; Logical events represented by AND, OR and NOT; The meaning, expression rules and methods of truth table of logical function.

Writeable: logical expressions, truth tables, logical symbols and their laws of logical AND, OR, NOT, NOR, XOR, XOR, etc. Transformation between logic function, truth table and logic diagram; Logical expression of negative logical symbols.

We can use: logic algebra to simplify logic functions; The minimum term and its number represent logical functions; Karnaugh map simplifies logical functions.

2. Integrated logic gate circuit

It is necessary to know the relationship between high level, low level and positive and negative logic states of logic circuits. The relationship between the meaning of threshold voltage UTH of CMOS inverter and VDD. The difference of UTH value between 74H and 74LS, the significance of main parameters of integrated logic circuit and the performance. The difference between the meaning of non-symbols and small circles on the symbols at the control end of logical symbols and the meaning of small circle symbols on gate circuits. The function of three-state gate enable control and the significance of output high resistance.

The logical symbols of OD gate, OC gate, transmission gate and tri-state gate will be drawn. The output waveform corresponds to the input waveform of AND gate, OR gate, NOT gate, NAND gate and NOR gate.

The functions of OC gate, OD gate, transmission gate and tri-state gate can be used.

It will involve: storage and welding measures of CMOS integrated logic circuits, standby input terminals of various gate circuits, and interfaces between various gate circuits.

3. Combinatorial logic circuit

You should know: the characteristics of combinational logic circuits, the analysis steps and design steps of combinational logic circuits. Meaning of encoder, decoder, data distributor and data selector.

Can analyze: simplify the logic function of combinational logic circuit described by expression and truth table with logic function.

Will design: set the meaning and logic state of input and output variables according to logical events, list truth tables according to causality, write logic function formulas and simplify logic diagrams.

You can use the pin functions of encoders, priority encoders, decoders, digital seven-segment decoders and data selectors of various medium-sized integrated devices represented by function tables.

Can draw: circuit diagram of AND or logic function with decoder or digital selector.

4. Integrated trigger

We should know the working characteristics of flip-flop, basic RS flip-flop, synchronous flip-flop and pulse edge flip-flop, as well as the functions of T and T' flip-flops.

The circuit and logic symbol diagram of basic RS flip-flop composed of NAND gate and NOR gate, D flip-flop triggered by rising edge, JK flip-flop triggered by falling edge, logic symbol diagram and its output waveform diagram, and connection diagram of T' flip-flop composed of JK and D flip-flop will be drawn.

Can write the state equation of RS trigger, D trigger and JK trigger.

Will recite: the relationship between the state of output Q of JK flip-flop and the state of input JK under the action of CP falling edge.

Will be used: integrated flip-flop directly set, reset terminals SD, RD, and, state setting methods in various situations.

5, sequential logic circuit

We should know the working characteristics of sequential logic circuits, the analysis methods of synchronous sequential logic circuits, and the functions of registers, shift registers and counters. The meaning of synchronization and asynchronism.

Will use: the menu reflected by the bidirectional shift register, various types and models of medium-sized integrated counter pin functions, asynchronous and synchronous clearing or setting.

By means of feedback clearing and feedback setting, the wiring of N-ary counter circuit under asynchronous or synchronous conditions is drawn.

6, pulse circuit

You should know: the function of differential and integral circuits; The function of each pin of 555 timer and the logic law of its threshold input and output terminal voltage; Basic functions of monostable trigger, multivibrator and Schmidt trigger.

Will choose: the circuit structure type that realizes the functions of pulse width timing, delay control pulse, pulse width modulation, waveform transformation, shaping, acoustic power supply, clock pulse, standard time base pulse signal, etc.

Will identify: the requirements of various types of monostable flip-flops for input trigger pulse width and the types of effective flip-flops.

It will be concluded that Schmidt triggers waveform conversion or shapes the output waveform.

Can be calculated: the output pulse width of flip-flops with various structures and the oscillation frequency of multivibrators with various structures.

7. Semiconductor memory

We need to know: the logical functions of read-only memory (ROM) and random access memory (RAM) and their differences in performance, the function of memory address decoder, and the relationship between address input line and word line W subscript I value; Meaning of word line, bit line, memory cell, word length and byte. The function of mask read-only memory and programmable read-only memory and the difference of their memory cell circuits. Three types of PROM and their differences in working performance. The difference between two kinds of circuit memory cell structures in RAM.

The storage capacity of semiconductor memory can be calculated.

Will draw: RAM storage capacity word expansion and bit expansion circuit and its connection.

8. D/A and A/D converters

We should know: the function of digital-to-analog converter and analog-to-digital converter, the relationship between input digital quantity and output voltage of R-2R inverted T-shaped resistance network DAC; The meaning of sampling/holding, quantization and coding of digital-to-analog converter, the basic working principle and characteristics of V-T double integration and successive approximation A/D converter.

The resolution of ADC or DAC with different digits expressed by voltage value and the maximum allowable absolute error are calculated.

The first course of digital circuit is the foundation of circuit analysis and analog circuit, and the subsequent courses are microcomputer principle, microcomputer and interface technology.

There are great differences between digital circuits and analog circuits in research objects and methods. Table 1.5. 1 makes a simple comparison between the two.

Table 1.5. 1 Comparison between analog and digital circuits

Internal analog analog circuit digital circuit

Working signal analog signal digital signal

Amplification of pipeline working state

Saturation on or off

Magnification performance of research object

logical function

Basic unit circuit amplifier

Logic gates and flip-flops

Graphic method of analytical tools and equivalent circuit method of micro-variation.

Truth table, Karnaugh map, logical expression, state transition diagram, Boolean algebra.

Obviously, there is a great difference between analog circuits and digital circuits. Beginners should make some changes in their learning methods to adapt to the characteristics of digital circuits in order to achieve good results.

1. In digital circuits, all variables are reduced to two opposite states: 0 and 1. Usually, we only need to care about whether there is a signal, the level, the on-off of the switch, etc., and we don't need to pay attention to the detailed value of a variable. For example, a small change in the level amplitude may be meaningless.

2. The research method of digital circuit is based on logic algebra (also called Boolean algebra). It mainly studies the logical relationship between input and output variables, and establishes a set of operation and simplification methods of logical functions. Boolean algebra, also called binary algebra, has only two possibilities: 0 and 1. Compared with analog circuits, digital circuits have no complicated calculation problems.

3. Due to the high development of digital integrated circuit technology, digital circuits more clearly reflect the characteristics of pipeline integration. Novices should pay full attention to this feature. Generally speaking, learning circuit structure is not our purpose, but mastering circuit function.

Digital system usually consists of input interface, output interface, data processing and controller. The main tasks of input interface and output interface are to convert analog quantity into digital quantity, or to convert digital quantity into analog quantity. The main function of the processor is to control the work of various components in the system and make them run according to certain programs. Whether there is a controller is usually used as a sign to distinguish functional components from digital systems. Any system that contains controllers and can run in sequence, regardless of its size, is called a digital system.