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QUAID-E-AWAM UNIVERSITY OF ENGINEERING SCIENCE & TECHNOLOGY NAWABSHAH

DEPARTMENT OF TELECOMMUNICATION ENGINEERING Subject: DIGITAL LOGIC DESIGN

BATCH – 14TC (1ST TERM – 2ND YEAR)

LAB EXPERIMENT # 09

ENCODER & DECODER PERFORMANCE OBJECTIVE: 

To implement and verify experimentally decoder & encoder operation.  Using the Edibon Trainer M-15  Using IC 74LS47 Encoder & BCD-to-7 segment decoder

EQUIPMENT:  Edibon Power supply unit (FA-CO)  Edibon Trainer M-15

COMPONENTS:    

IC 74 LS147(10 line decimal to 4 line BCD priority encoder) For LEDs Resister 330 ohms Connecting wires, Hardwires.

DISCUSSION: Encoder is a circuit whose function is to converts octal or decimal input into binary output.

Fig: 9.1 (a) In the encoder circuit shown in fig: 9 (c); the four OR gates are connected in such a way that when any decimal push button is pressed, the output on A, B, C, D results in binary. The operation of circuit is not much difficult. A little concentration will let you know about the operation of circuit.

PIN DECRIPTION: 74LS47 is a 10 line decimal to 4 line BCD encoder. At same time it is also as a priority encoder. Q1 to Q2 are inputs while A, B, C & D are outputs. The ( -) bar over input and outputs indicate that inputs as well as outputs are active low means these pins will be activated when connected to GND or low output will be demonstrated.

Fig: 9.1 (b)

Fig: 9.1 (c)

PROCEDURE:  11,12, 13 , 1 ,2 ,3 , 4 ,5, 10 ,=Q1 to Q9 (inputs),  14, 6, 7, 9, (A ,B,C,D,)=BCD outputs  8 =GND

 16 =VCC  15 =NC (Not Connected) The 74147 is connected above decorated with components, the device has nine decimal inputs i-e connected with switches, and four (BCD) outputs ie A, B, C, D. Each output is tied with +5v through a resister and Led , Note that all the inputs and outputs are bubbled. The presence of bubbles indicates that inputs and outputs are active low , in other words when any input is in traduced with GND through switch, it is recognized and corresponding output is activated on A,B,C,D outputs. Observation Table: INPUTS

OUTPUTS

1

2

3

4

5

6

7

8

9

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

0

1

1

1

1

1

1

1

0

1

1

1

1

1

1

1

0

1

1

1

1

1

1

1

0

1

1

1

1

1

1

1

0

1

1

1

1

1

1

1

0

1

1

1

1

1

1

1

0

1

1

1

1

1

1

1

0

1

1

1

1

1

1

1

0

1

1

1

1

1

1

1

1

D’

C’

B’

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 that input number. In other words, a decoder circuit looks at its inputs, determine which binary number is present there, and activates the one output that corresponds to that number; all other outputs remain inactive. Decoding is the process of inverting some code (Such as binary, BCD, or Hex) into a singular active output representing its numeric value .The device, which perform job of decoding, is called Decoder. This device has not fixed number of inputs and outputs; they will be equal to the corresponding codes at input and

output. Take for example a system reads 4-bit BCD code and converts it into its appropriate decimal number must have 4 inputs and ten outputs. This is also called a BCD –to-Decimal decoder or 1-to-10 decoder or 4-to -10 decoder. The corresponding output results of BCD –to-Decimal decoder will be look like as shown in fig. 9.2.

fig. 9.2 (a) Fig. 9.2 (b) and (c) shows seven-segment display for BCD –to-Decimal decoder. While fig (d) shows the BCD- to–decimal decoder IC.

Fig: 9.2 (b)

Fig: 9.2 (c)

Fig: 9.2 (d)

74LS47 DECODER IC:

Fig: 9.3 The 74LS47 accepts four lines of BCD (8421) input data, generates their complements internally and decodes the data with seven AND/OR gates having open-collector outputs to drive indicator segments directly. Where RBI : Ripple Blank Input (Active Low) BI RBO : Blanking Input (Active LOW) or Ripple Blanking Output (Active LOW) a  g : Segment Outputs (Active LOW) A-D: BCD Inputs.

PROCEDURE: 

Take digital Electronics module E18 and apply 5V power supply from power supply unit (EV).



There is standard symbol for Decimal –to-BCD decoder on trainer.



Connect inputs A, B, C and D to the switches.



Connect 1, 2,3,4,5,6,7,8, and 9 to the corresponding leads of the 7segment display.



Set all combination of observation table with help of switches and fill the observation table.

OBSERVATION TABLE:

Inputs D C B 0 0 0

A 0

0

0

0

1

0

0

1

0

0

0

1

1

0

1

0

0

0

1

0

1

0

1

1

0

0

1

1

1

1

0

0

0

1

0

0

1

0

1

2

3

Outputs 4 5 6 7

8

9

REVIEW QUESTIONS: 1. What is function of LT, RBO, and RBI inputs? 2. What is the meaning of bubbles on the outputs of 7447 IC? 3. Which input is used to test all segments of 7-segment display? 4. What will be 7-segment display read with applying 1001 combination on decoder inputs? 5. What are the applications of the decoders? 6. What is an encoder? What its main purpose?

7. What is decoder? What is main purpose? 8. What do you mean by priority encoder?

Roll No: Remarks:

Signature of Teacher: Date:...