Binary code of N digits can be used to store 2N distinct elements of coded information. This is what encoders and decoders are used for. Encoders convert 2N lines of input into a code of N bits and Decoders decode the N bits into 2N lines.

1. Encoders – An encoder is a combinational circuit that converts binary information in the form of a 2N input lines into N output lines, which represent N bit code for the input. For simple encoders, it is assumed that only one input line is active at a time.

As an example, let’s consider Octal to Binary encoder. As shown in the following figure, an octal-to-binary encoder takes 8 input lines and generates 3 output lines.

Implementation –

X = D4 + D5 + D6 + D7 Y = D2 +D3 + D6 + D7 Z = D1 + D3 + D5 + D7 Hence, the encoder can be realised with OR gates as follows:

A decoder does the opposite job of an encoder. It is a combinational circuit that converts n lines of input into 2n lines of output.

Let’s take an example of 3-to-8 line decoder. Implementation – D0 is high when X = 0, Y = 0 and Z = 0. Hence,

D0 = X’ Y’ Z’ Similarly,

D1 = X’ Y’ Z D2 = X’ Y Z’ D3 = X’ Y Z D4 = X Y’ Z’ D5 = X Y’ Z D6 = X Y Z’ D7 = X Y Z

/*

Open Quartus II and select new project and choose the file location.

Module Declaration. Module should have the file name.

Input-Output Delecaration.

Use assign to define the functionality of logic circuits.

At the end give endmodule.

Run the program and choose RTL viewer to get RTL realization. */

/* Program for Endocers and Decoders and verify its truth table in quartus using Verilog programming. Developed by: LOGESHWARI.P RegisterNumber:212221230055
*/

module Encoder(a,b,c,d0,d1,d2,d3,d4,d5,d6,d7);
input d0,d1,d2,d3,d4,d5,d6,d7;
output a,b,c;
or(a,d4,d5,d6,d7);
or(b,d2,d3,d6,d7);
or(c,d1,d3,d5,d7);
endmodule

module Decoder(d0,d1,d2,d3,d4,d5,d6,d7,a,b,c);
input a,b,c;
output d0,d1,d2,d3,d4,d5,d6,d7;
assign d0 = (~a&~b&~c);
assign d1 = (~a&~b&c);
assign d2 = (~a&b&~c);
assign d3 = (~a&b&c);
assign d4 = (a&~b&~c);
assign d5 = (a&~b&c);
assign d6 = (a&b&~c);
assign d7 = (a&b&c);
endmodule

Thus, 8 to 3 Encoder and 3 to 8 Decoder is implemented using verilog and its outputs is validated.