Analysis and research of display decoder design in digital circuit - Power Circuit - Circuit Diagram
Abstract: In view of the problem that the input and output variables are difficult to determine when designing the decoder, a functional analysis and variable association design method is proposed. The display decoder output is driven by the driver to operate the display. The amount and state of the output variable depends on the type of display, and the number and state of the input variables are related to the output display result. Studies have shown that the number of bits of the input variable of the decoder is displayed, and n is equal to 2n=N or 2n-1 between the number of output display results.
Display decoder is a very important device in the digital electronic technology combination logic circuit. It is indispensable in the application of digital electronic technology. Especially in today's digitalization of information technology, its application is more and more extensive, but it is organized to carry out technological innovation and In the electronic design and production competition, when designing and making electronic products such as responders, scorers, chronographs, etc., students always have an infinite number of display decoders that accurately design the functional requirements. This paper analyzes this problem. And research.
1 Display the function and type of the decoder The logic circuit that implements the decoding function is the decoder. Decoding is the inverse of encoding. In a digital system, any information or data, whether text, numbers, symbols or graphics, is converted to binary code during monitoring, control, and transmission. This is the encoding; During the control, transmission process or at the end, the corresponding information processing result must be displayed. This must restore the binary code to the corresponding text, number, symbol or graphic. This process is decoding. In digital electronic technology, there are two types of decoders, a variable decoder and a display decoder.
The variable decoder is divided into binary and non-binary. The binary decoder is N=2n between the number of bits of the input binary code and the number N of the decoded output information. The non-binary decoder cannot A decoder that satisfies this relationship.
The display decoder displays text, numbers, symbols, etc., and the display materials include fluorescent, liquid crystal, LED, etc., and the display forms are segmented, superimposed, dot matrix, etc. Common cathodes and common anodes and so on.
Both the variable decoder and the display decoder have some commonly used stereotypes, such as a binary three-line-eight-line decoder, that is, input three-digit binary code, and output eight information, satisfying 23=8. The commonly used integrated chips are the 74 series and the 54 series. The most typical chip is the 74LS138. The most typical display decoder is a non-binary decimal number decoder, model 74LS48. However, in practical applications and innovative designs, these products are not enough to meet the requirements of different functions, and a new display decoder must be designed. In the design process, the most problematic is the determination of input and output variables when designing the display decoder. .
2 Display decoder design steps show that the decoder is a combination logic circuit in digital electronic technology, so in design, the design method of the combination logic circuit should also be followed. There are four steps: First, determine the location according to the functional requirements. Design circuit input and output variables and their meanings; second, list the truth table according to the requirements of the function; third, use the Karnaugh map to simplify the logical expression of the input and output variables; fourth is based on the logical expression Draw a logic diagram.
From the past teaching practice, skill competition and extracurricular activities, it is found that in the four steps of the combination logic circuit design, the difficulty in designing each type of circuit is different. For example, when designing a combinational logic circuit with input and output variables in binary relationship, the most important thing is that the second step lists the truth table according to the functional requirements. When designing the combination logic circuit with non-binary features, the key point is to grasp The third step is to simplify the Karnaugh map with constraints. When the design requires the combination of logic components with specified components, the design difficulty is the fourth step. The simplified logical expression must be converted to the design requirements. The functional relationship realized by the specified components, and then draw the logic diagram; then when designing the display decoder, the most confusing and unclear is the first step in the design process.
3 Display decoder design skills According to the combination logic circuit design method, according to the characteristics of display decoder, combined with the outstanding problems in design practice, the first step in the design process of display decoder is analyzed and studied. , how to accurately determine the input and output variables of the circuit design and methods.
First of all, we must understand the role of the display decoder in the digital circuit, and confirm its functional relationship in the display circuit, as shown in Figure 1, the digital display circuit is shown by the display decoder, display driver and result display It consists of several parts. The display decoder is to decode, control, and transmit the binary code in the digital circuit, and then decode and restore the information into corresponding text, numbers, symbols, etc., and display them in different forms; the display driver ensures that the result display is normal. The working circuit, according to the result of the display material, power, circuit, using current limiting resistor drive, Darlington drive, relay drive and other methods; display display content, methods, etc., the most common stereotypes are Seven-segment digital display tube. Therefore, when designing and displaying the decoder, it is necessary to consider the three parts of the decoder, the driver and the display.
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