Encoder and Input Lines

Experiment 1 - Decoders, Encoders

Objectives:

To design a 2-4 decoder

To design a 4-2 encoder

To use a 7442 IC for BCD to decimal conversion

Required IC’s:

7408 AND Gate

7432 OR Gate
7400 NAND Gate
7404 INV Gate
7474 D Latch
7442 BCD to Decimal converter

Theory:

Decoders

The basic function of a decoder is to detect the presence of a particular combination of bits at the inputs and indicate the presence of that particular set of bits by outputting a specified output level. Typically a decoder with n input lines require 2n output lines to decode every possible combination of bits. BCD to decimal conversion, looked at in part 3 of this lab, is accomplished using a decoder which has 4 input lines and 10 output lines (the 10 output lines correspond to the decimal numbers 0-9). This device is used to convert between binary numbers and decimal numbers.

Encoders:

An encoder performs the opposite function of a decoder. An encoder takes a input on one of its 2n input lines and converts it to a coded output with n lines.

Part 1. Analysis of a Decoder

Procedure:

Set up the circuit as shown on page 4. In this circuit X & Y are the encoded inputs and A, B, C, D are the decoded outputs. For this circuit

Vary the inputs (for all possible combinations of inputs) and note the corresponding outputs.

Construct the truth table

Part 2. Analysis of an Encoder

Procedure:

Set up the 4-2 encoder circuit shown on page 5. In this circuit A, B, C, D are the four inputs and X & Y are the encoded outputs. For this circuit:

Vary the inputs (For all possible combination of inputs) and note the outputs.

Construct the truth table.

Use a K-map to determine the circuitry involved in the encoding process

Part 3. BCD to Decimal conversion

Procedure:

Set up the BCD to decimal conversion circuit as shown on page 5. For this circuit:

Vary the inputs (4 BCD inputs) and record the outputs.

Construct the