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Computer Logic DesignEE-106

Lab # 7 Manual

Name: _________________________________________

Reg. No: ________________________________________

Section: _________

National University of Computer & Emerging Sciences, Islamabad

Prepared by: Jahanzaib Zafar , Ayman Bukhari 

Checked by:

Date:

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  Experiment # 7

Experiment Title:

Decoder and Priority Encoder

Lab Tasks:1) Implementation of 3 to 8 line decoder2) Design and Implement the full adder by using decoder3) Design the 4 to 16 line decoder by using 2 to 4 decoder4) Implementation of Priority Encoder

Objectives:

Practicing the implementation of logic functions using MSI levelFunctional blocks

Gaining experience with MSI level functional blocks/componentsWhose outputs are active low.

Gaining a close insight into the functioning and properties of decoderCircuits

Developing skills in the design and testing of combinational logic

Circuits.

Equipment Required:

DEV-2765E Trainer Board

74LS138 (3-to-8 Decoder)

74LS148 (8-bit Priority Binary Encoder)

Background Theory

Decoder is a multiple input, multiple output logic circuit that converts coded input

into coded output, where the input and output codes are different. The input codegenerally has fewer bits than the output code, and there is one-to-one mapping,each input code word produces a different output code word. The mostcommonly used input code is an n-bit binary code, where an n-bit wordrepresents one of 2n different coded values, i.e n-to-2n decoder or binarydecoder.Encoder is a logic circuit that has fewer output bits than the input code. Theencoder takes 2n inputs bits and generates n-bit output. Only one of the inputs

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can be 1, and the corresponding binary will display on the output bits. But whenmore than one input bits become 1 at the same time then what should be theoutput then? So we give priority to inputs and the input with high priority willfreeze the output with its binary value. Such an encoder is called priority encoder .

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Task 4: Design the 4 to 16 line decoder by using 2 to 4 decoder

Lab performed on (date): ___________ Signature: ______________

Checked by: ________________________ Date: ______________

Marks Awarded: ____________

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