EncodersThe combinational circuits that change the binary information into N output lines are known as Encoders. The binary information is passed in the form of 2^{N} input lines. The output lines define the Nbit code for the binary information. In simple words, the Encoder performs the reverse operation of the Decoder. At a time, only one input line is activated for simplicity. The produced Nbit output code is equivalent to the binary information. There are various types of encoders which are as follows: 4 to 2 line Encoder:In 4 to 2 line encoder, there are total of four inputs, i.e., Y_{0}, Y_{1}, Y_{2}, and Y_{3}, and two outputs, i.e., A_{0} and A_{1}. In 4input lines, one inputline is set to true at a time to get the respective binary code in the output side. Below are the block diagram and the truth table of the 4 to 2 line encoder. Block Diagram:Truth Table:The logical expression of the term A0 and A1 is as follows: A_{1}=Y_{3}+Y_{2} Logical circuit of the above expressions is given below: 8 to 3 line Encoder:The 8 to 3 line Encoder is also known as Octal to Binary Encoder. In 8 to 3 line encoder, there is a total of eight inputs, i.e., Y_{0}, Y_{1}, Y_{2}, Y_{3}, Y_{4}, Y_{5}, Y_{6}, and Y_{7} and three outputs, i.e., A_{0}, A1, and A_{2}. In 8input lines, one inputline is set to true at a time to get the respective binary code in the output side. Below are the block diagram and the truth table of the 8 to 3 line encoder. Block Diagram:Truth Table:The logical expression of the term A0, A1, and A2 are as follows: A_{2}=Y_{4}+Y_{5}+Y_{6}+Y_{7} Logical circuit of the above expressions is given below: Decimal to BCD EncoderThe Octal to Binary Encoder is also known as 10 to 4 line Encoder. In 10 to 4 line encoder, there are total of ten inputs, i.e., Y_{0}, Y_{1}, Y_{2}, Y_{3}, Y_{4}, Y_{5}, Y_{6}, Y_{7}, Y_{8}, and Y_{9} and four outputs, i.e., A_{0}, A1, A_{2}, and A_{3}. In 10input lines, one inputline is set to true at a time to get the respective BCD code in the output side. The block diagram and the truth table of the decimal to BCD encoder are given below. Block Diagram:Truth Table:The logical expression of the term A_{0}, A_{1}, A_{2}, and A_{3} is as follows: A3 = Y9 + Y8 Logical circuit of the above expressions is given below: Priority Encoder:4 to 2 line Priority Encoder:In this priority encoder, there are total of 4 inputs, i.e., Y_{0}, Y_{1}, Y_{2}, and Y_{3}, and two outputs, i.e., A_{0} and A_{1}. The Y_{3} has high and Y_{0} has low priority inputs. When more than one input is '1' at the same time, the output will be the (binary) code corresponding to the higher priority input. Below is the truth table of the 4 to 2 line priority encoder. Truth Table:The logical expression of the term A_{0} and A_{1} can be found using Kmap as: A_{1}=Y_{3}+Y_{2} Logical circuit of the above expressions is given below: Uses of Encoders:
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