Design

There are two basic designs of logical circuits

1)Combinational Circuits

2)Sequential Circuits

Our interest is only in Combinational circuits and there applications. There are following steps to design combinational circuits.

1-Find number of inputs/outputs from problem statement.

2-Assign different letters to inputs and outputs e.g X,Y,Z,a,b,c etc.

3-Write truth table of problem.

4-Write simplified Boolean’s equation from truth table for each output.

5-Implement the circuit.

encoder

is a combinational logic circuit if there are 2^n input lines they will produce n number of outputs. There are following encoder combinations

1) 4 : 2 Encoder

2) 8 : 3 Encoder

3)16 : 4 Encoder

Boolean Equation:

Q1 = D2 + D3

Q0 = D1 + D3

Decoder

is totally opposite to encoder which have n number of inputs and provide us 2^n number of outputs. If we have 3 inputs D0 , D1 , D2  and there preference started from left to right when all are 0 then output is also zero but when the input is 1 then we can see output 1 showing result and then so on.

There are  following decoder combinations

1)1 : 2 Decoder

2)2 : 4 Decoder

3)3 : 8 Decoder

2*4 decoder have 2 inputs and 4 outputs. Decoders are also used in 7-segment display.

 

Priority Encoder

As the name stated it depends upon priority function. If the two or more inputs have input 1 at the same time, the input having highest priority will take precedence.

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Logic gates

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