Encoders and decoders

For students

1. Encoders & Decoders Combinational Logic

2. GROUP MEMBERS ABDUL BASIT - 14CS01 HAMMAD RASHID - 14CS39 UMAIR SIMJEE - 14CS71 HAFIZ FAIZAN - 14CS15

3. INTRODUCTION Encoders and Decoders are combinational logic circuits. Combinatorial logic is a concept in which two or more input states define one or more output states. We Implement Combinational logic circuit using Boolean Algebra. Combinational logic is used in circuits to perform Boolean algebra on input signals. Part Of ALU processes, That performs mathematics is carried out through combinational logics.

4. Contd. An encoder is a device which transforms the data into some bits known only to it and the decoder is a device which transforms those coded bits to generate the original data again . Encoding and Decoding is done for the safe transmission of data. To encode something is to convert an unambiguous piece of information into a form of code that is not so clearly understood. To decode is to perform the reverse operation: converting a code back into an unambiguous form . The Main Difference between a decoder and encoder is that a decoder has binary code as an input while an encoder has binary code as an output.

5. ENCODER An encoder is an electronic device used to convert an analogue signal to a digital signal. It has a number of input lines, but only one of the inputs is activated at a given time and produces an N-bit output code that depends on the activated input .

6. ENCODER SCHEMATIC DIAGRAM The encoder accepts 2^N inputs and produces N-number of outputs. For example, in 4-2 encoder, if we give 4 inputs it produces only 2 outputs. When we have 8 bits encoder, it means N = 3 and the output will be 3 binary digit output.

7. ENCODER TRUTH TABLE The value of output depends upon the logic gate being used. Different gates yield different output.

8. ENCODER Octal To Binary Encoder Octal-to-Binary take 8 inputs and provides 3 outputs. At any one time, only one input line has a value of 1 . Truth Table

9. ENCODER SCHEMATIC DIAGRAM

10. ENCODER PRIORITY ENCODER A priority encoder is a circuit or algorithm that compresses multiple binary inputs into a smaller number of outputs. If 2 or more inputs are equal to 1 at the same time, the input having the highest priority will take precedence. Internal hardware will check this condition and priority is set.

11. ENCODER 4 BIT PRIORITY ENCODER – TRUTH TABLE

12. DECODER A decoder is a logic circuit that accepts a set of inputs that represents a binary number and activates only the output that corresponds to the input number. In other words, a decoder circuit looks at its inputs, determines which binary number is present there, and activates the one output that corresponds to that number, all other outputs remain inactive.

13. DECODER A decoder is a circuit that changes a code into a set of signals. In its general form, a decoder has N input lines to handle N bits and form one to 2^N output lines to indicate the presence of one or more N-bit combinations . An AND gate can be used as the basic decoding element because it produces a high output only when all inputs are high.

14. DECODER Binary decoder 2-bit decoder 3-bit decoder BCD-to-decimal decoder BCD-to-Seven-Segment Decoder

15. DECODER Binary decoder The output is 1 only when: A = 1 A 2 = 0 A 3 = 0 A 4 = 1

16. DECODER 2 TO 4 LINE DECODER – SCHEMATIC DIAGRAM and TRUTH TABLE

17. DECODER 3 TO 8 LINE DECODER – TRUTH TABLE

18. DECODER 3 TO 8 LINE DECODER – SCHEMATIC DIAGRAM

19. DECODER BCD TO DECIMAL DECODER

20. DECODER BCD TO SEVEN SEGMENT DECODER Digital readouts on many digital products often use LED seven-segment displays. Each digit is created by lighting the appropriate segments. The segments are labeled a,b,c,d,e,f,g The decoder takes a BCD input and outputs the correct code for the seven-segment display.