Encoders

 Encoders

An Encoder is a combinational circuit that performs the reverse operation of Decoder.

It has maximum of 2n input lines and ‘n’ output lines. 

It will produce a binary code equivalent to the input, which is active High

The encoder encodes 2n input lines with ‘n’ bits. It is optional to represent the enable signal in encoders.

4 to 2 Encoder

 It has 4 inputs and 2 outputs

Truth Table

This is the truth table of 4 to 2 Encoder

Inputs				Outputs
Y3	Y2	Y1	Y0	A1	A0
0	0	0	1	0	0
0	0	1	0	0	1
0	1	0	0	1	0
1	0	0	0	1	1

when case Y2 is one and Y3 is one , A1 is one. Therefore we can say,

A1 = Y3 + Y2

when case Y1 is one and Y3 is one , A0 is one. Therefore we can say,

A0 = Y3 + Y1

Circuit

Encoders are designed with logic gate such as an OR-gate

How to draw 4 to 2 Encoder and simulate

click on the arrow icon

create circuit with two OR Gates

Set Wires 

put inputs and outputs

click on the Simulate icon

Simulate Circuit

Octal to Binary Encoder

Octal to binary Encoder has eight inputs, Y7 to Y0 and three outputs A2, A1 & A0

 

Truth Table of Octal to Binary Encoder

 

At any time, only one of these eight inputs can be ‘1’ in order to get the respective binary code

Inputs								Outputs
Y7	Y6	Y5	Y4	Y3	Y2	Y1	Y0	A2	A1	A0
0	0	0	0	0	0	0	1	0	0	0
0	0	0	0	0	0	1	0	0	0	1
0	0	0	0	0	1	0	0	0	1	0
0	0	0	0	1	0	0	0	0	1	1
0	0	0	1	0	0	0	0	1	0	0
0	0	1	0	0	0	0	0	1	0	1
0	1	0	0	0	0	0	0	1	1	0
1	0	0	0	0	0	0	0	1	1	1

   

Explanation

A2=Y7+Y6+Y5+Y4$$$$

A1=Y7+Y6+Y3+Y2 

A0=Y7+Y5+Y3+Y1

Circuit

How to create and Simulate

click on the arrow icon

create circuit with two OR Gates

Set Wires 

put inputs and outputs

click on the Simulate icon

Simulate Circuit

This is to opposite in 3 - 8 Decoder

It accepts eight inputs and produces 3 bit output codes. 

Priority Encoder

Four inputs, Y3, Y2, Y1, and Y0, and two outputs, A1 and A0, make up a 4 to 2 priority encoder. The input Y3 is given the highest priority, whereas the input Y0 is given the lowest. Even if more than one input is ‘1' at the same time in this situation, the output will be the binary code corresponding to the input with greater priority.

We looked at another output, V, to see if the code at the outputs was correct.

• The code available at the outputs is valid if at least one of the encoder's inputs is "1." V will equal 1 in this situation
• If all of the encoder's inputs are zero, the code that appears on the outputs is invalid. V will be equal to 0 in this situation.

Truth Table of 4 to 2 Priority Encoder

Inputs				Outputs
Y3	Y2	Y1	Y0	A1	A0	V
0	0	0	0	0	0	0
0	0	0	1	0	0	1
0	0	1	x	0	1	1
0	1	x	x	1	0	1
1	x	x	x	1	1	1

 

The simplified Boolean functions are

A1=Y3+Y2

A0=Y3+Y2′Y1

Similarly, we will get the Boolean function of output, V as

V=Y3+Y2+Y1+Y0

V=Y3+Y2+Y1+Y0

3

0

How to create Circuit and Simulate

Circuit diagram contains two 2-input OR gates, one 4-input OR gate, one 2input AND gate & an inverter.

Even though many inputs are equivalent to ‘1' at the same time, an AND gate and inverter combination is employed to provide a valid code at the outputs. As a result, based on the priority assigned to each input, this circuit encodes the four inputs with two bits.