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- 1. Practical WorkbookLogic Design & Switching Theory I Name : _____________________________ Year : __________ Batch: ____________ Roll No. : _____________________________ Group No. : ____________________________ Department : ____________________________ Dept. of Computer & Information Systems Engineering NED University of Engineering & Technology, Karachi – 75270, Pakistan
- 2. Practical Workbook Logic Design & Switching Theory IPrepared By: M. Anwar Ali Khan (Asst. Professor) & Muhammad Mazher Alam (Ex - Asst. Professor)Revised By: Maria Waqas (Lecturer) Second Edition Fourth Reprint – 2010 Dept. of Computer & Information Systems Engineering NED University of Engineering & Technology, Karachi – 75270, Pakistan
- 3. THE BITS AND PIECESPART CIRCUIT WHAT IT DOES SIGN Supplies a voltage which drives an electric current round the circuit from the positive (+) terminal of the battery to its negative (–) terminal. Voltage is measured in volts (V) and current in amperes (A). Allows current to flow through it easily because it is made of copper which is a good electrical conductor. Insulators like PVC (polyvinyl chloride - a plastic) and enamel are used to cover connecting wires. Connects terminal A to terminal B or C, i.e. it is a change-over switch. Reduces the current in a circuit because of its resistance. The colored bands give the resistance in ohms. When light falls on it, its resistance becomes small; in the dark its resistance is high. 3
- 4. PART CIRCUIT WHAT IT DOES SIGN Stores electricity; the greater the capaci- tance the more does it store. Capacitance values are measured in microfarads shortened to μF or, less correctly, to mfd. On a capacitor, 0.1 μF may be marked as .l mfd and 0.01μF as 10n. The greatest voltage it can stand is also shown, e.g. 30V. Stores electricity: values usually larger than 1μF. Greatest voltage marked on it. Must be connected the correct way round. Varies the capacitance in a circuit by mov- ing one set of metal plates in or out of a fixed set when the spindle is rotated. The sets of plates are separated by sheets of an insulator (also called a dielectric). Changes electric currents into sound. Changes radio waves into electric currents. Lets current flow in one direction but not in the other. When it conducts, light is emit- ted. Must have a current limiting resistor in series with it. The cathode lead is nearest the ‘flat’ and may be shorter than the anode lead (but this is not always so). The arrow on the sign shows the conducting direction. 4
- 5. PART CIRCUIT WHAT IT DOES SIGN Amplifies small currents into much larger copies. Acts as a very fast switch. It must be correctly connected with a positive voltage to the collector. Transistors, diodes, resistors and capacitors are connected together on a tiny ‘chip’ of silicon (sand is mostly silicon oxide) to give any desired circuit, e.g. a multistage amplifier; an astable, bistable or monostable multivibrator; a counter; a logic gate for a computer; several stages of a TRF (tuned radio frequency) radio. They must be correctly connected. Pin 1 is next to the ‘tag’ in the can type and on the d.i.l. type it is identified from the ‘notch’ or ‘small dot’ on the case. CMOS ‘chips’ (standing for Complementary Metal Oxide Semiconductors and pronounced ‘see- moss’) need special care. PRECAUTIONS WITH CMOS INTEGRATED CIRCUITSDamage occurs if static charges build up on input pins when, for example, they touchinsulating materials (e.g. clothes, plastic pen) in warm, dry conditions.1. Keep the IC in the carrier in which it is supplied until it is inserted in the circuit.2. Do not finger the pins or hold them in contact with an insulator.3. Connect all unused inputs of the IC to either the positive or the negative of the battery, depending on the circuit. 5
- 6. BUILDING CIRCUITSThe circuit board shown above accepts ICs as well as separate components. It has 47 rows of 5interconnected sockets on each side of a central channel across which d.i.l. ICs can be fitted.A wire inserted in a socket in a certain row becomes connected to wires in any of the other 4sockets in that row by a metal strip under the board. For example, wires in sockets B5, C5, D5,E5 and F5 (shown in color in the diagram) are all joined. Metal strips under the board connectthe sockets.A row of 40 interconnected sockets along the top of the board and a similar row along thebottom act as the positive and negative power supply rails (called ‘bus bars’).Various makes of circuit board are available, some with vertically mounting removable panelsfor supporting controls. 6
- 7. 1. To make a connection push about 1 cm of the bare end of a wire (0.25 to 0.85 mm diameter) straight into the socket (not at an angle) so that it is gripped by the metal strip under the board. Do not use wires that are dirty or have kinked ends. Only put one wire in each socket. Bend leads on resistors etc., as shown before inserting them in the board.2. Bare the ends of connecting wire (PVC-covered tinned copper wire 0.6 mm diameter) by removing the insulation (PVC) either with wire strippers or using a pair of blunt-nosed pliers and a pair of side cutters as shown. With practice you should be able to judge just how much the side cutters have to be squeezed and pulled to remove the insulation without cutting the wire.3. ‘Join’ wires to the ‘lugs’ on the loudspeaker and variable capacitor using a small length of 2 mm bore plastic sleeving - as shown by 1 and 2. 7
- 8. RESISTOR COLOUR CODEResistor values are given in ohms (shortened to Ω, the Greek letter ‘omega’). They are markedon the resistor using a color code.Three colored bands are painted round the resistor. Each color stands for a number. To read thecolor code, start at the 1st band; it is nearest the end. Sometimes it is not clear which is the 1stband because there is a 4th band of gold or silver near the other end. These two colors are notused for the 1st band; they give the accuracy of the resistor (gold is ± 5% and silver ± 10%), soyou should not have too much trouble deciding where to start.The 1st band gives the first number, the 2nd band gives the second number and the 3rd bandtells how many zeroes come after the first two numbers. 8
- 9. INTRODUCTIONDigital Logic Design is concerned with the interconnection among digital componentsand modules and the area of Switching Theory that can be identified between circuitdesign and system formulation. Logic design is the base of any computer system, asevery digital system consists of different IC’S and ICs contain a large number ofinterconnected digital circuits within a small package. MSI devices provide digitalfunction while LSI device cover a complete computer modules. These circuitries arewidely used in digital system like digital voltmeter, frequency meter, calculatingmachines, telephone-switching system etc.In this Practical Workbook, laboratory sessions based on both combinational andsequential logic are covered. First laboratory session gives an introduction to the basiclogic gates and fundamentals of circuit building.The second laboratory session covers a CAD software – Electronics Workbench (EWB).EWB is excellent simulation software, where circuits can be designed and tested beforephysical implementation. Various laboratory sessions of this workbook provide activitiesand exercises on EWB.Next eight laboratory sessions are based on combinational logic. Here various MSIcircuits, like adders, converters, multiplexers, decoders, encoders, etc, are designed.Some of these laboratory sessions also include testing of MSI ICs.Next four laboratory sessions help in exploring various designs based on sequential logic.Here a variety of circuits are designed, form the testing of basic flip-flop ICs to registersand different types of counters.Last laboratory session demonstrates how digital hardware can be interfaced with apersonal computer via parallel port and can be controlled by software.All laboratory sessions of this workbook incorporate brief theoretical backgrounds, asdetails may be covered in the respective theory classes. Exercises / activities are includedwith almost all the sessions for the students to practice.Two appendices are also included in this workbook. The first one provides pin diagramsfor all the ICs required for the laboratory work provided in this workbook. It will help thestudents in preparing the pin diagrams for the circuits. Second appendix discusses ahardware debouncing circuit for mechanical switches as such switches are extensivelyused for input purpose in logic circuits. 9
- 10. CONTENTSLab Session No. Object Page No. 1 To study the logic gates in the following TTL ICs. 13 7400 Quad 2-input NAND gate. 7402 Quad 2-input NOR gate. 7404 Hex inverter. 7408 Quad 2-input AND gate. 7432 Quad 2-input OR gate. Also, implementing and testing the given circuit on a bread board. 2 Working with Electronics Workbench. 17 3 Designing Half and Full Adder Circuits. 19 4 Use of Karnaugh Map (SOP-Expression) method. 22 5 Designing a BCD Adder. 28 6 Designing of a 4 x 1 Multiplexer. 30 Experimenting with 74150 IC. 7 Designing of a 2 x 4 Decoder / 1 x 4 Demultiplexer. 34 Experimenting with 74138 IC. 8 Designing of a 4 x 2 Priority Encoder. 38 Experimenting with 74148 IC. 9 Designing an Odd Parity Generator and Checker for a 3-bit Data. 42 10 Driving a seven segment display using 7447 / 7448 driver IC. 45 11 Experimenting with different modes of JK-FF. 48 12 Designing sequential circuit for the given state diagram using D flip-flop. 50 13 Designing a modulus-5 asynchronous up-counter using JK-FF. 54 14 Experimenting with 74194 4-bit bidirectional universal shift register 56 15 Experimenting with 74245 octal bus transceivers using parallel port PC 59 interfacing. Appendix A – Pin Diagrams of the ICs required for the laboratory sessions. 66 Appendix B – Debouncing circuitry for mechanical switches. 69 11
- 11. Logic Design & Switching Theory 1 Lab Session 01NED University of Engineering & Technology – Department of Computer & Information Systems Engineering Lab Session 01OBJECT • To study the logic gates in the following TTL ICs. i) 7400 Quad 2-input NAND gate. ii) 7402 Quad 2-input NOR gate. iii) 7404 Hex inverter. iv) 7408 Quad 2-input AND gate. v) 7432 Quad 2-input OR gate. • Implementing and testing the given circuit on a bread board.COMPONENTS REQUIRED1. Bread board2. 5 V - power supply3. Multimeter4. Logic probe5. LEDs with resistors6. Connecting wires7. Switches (optional)8. Following ICs and their datasheets: • 7408 quad 2 input AND gate • 7432 quad 2 input OR gate • 7404 hex inverter • 7400 quad 2 input NAND gate • 7402 quad 2 input NOR gateTHEORYLogic GatesLogic gates are the fundamental building blocks of digital systems. These devices areable to make decisions, in the sense that they produce one output level when somecombinations of input levels are present and a different output when other combinationsare applied; hence given the name Logic Gates. The two levels produced by digitalcircuitry are referred to variously as HIGH and LOW, TRUE and FALSE, ON and OFF,or simply 1 and 0. There are only three basic gates: AND, OR and NOT. The other gatesare merely combinations of these basic gates. Logic gates can be interconnected toperform a variety of logical operations. This interconnection of gates to achieveprescribed outcomes is called logic design.1. The AND Gate – An AND gate’s output is 1 if and only if all its inputs are 1. If A and B are two inputs to an AND gate then output, F of the gate is given as: F = A.B2. The OR Gate - An OR gate’s output is 1 if at least one of its input is 1. If A and B are two inputs to an OR gate then output, F of the gate is given as: F = A+B 13
- 12. Logic Design & Switching Theory 1 Lab Session 01NED University of Engineering & Technology – Department of Computer & Information Systems Engineering3. The NOT Gate (Inverter) – Its output is 1 when its input is 0 and its output is 0 when the input is 1; i.e. it complements a digital variable. If A is the input to a NOT gate then output, F of the gate is given as: F=A4. The NAND Gate – Its output is 1 if at least one of its input is 0. This gate performs the same logic as an AND gate followed by an inverter. If A and B are two inputs to a NAND gate then output, F of the gate is given as: F = A.B5. The NOR Gate - The output of a NOR gate is 1 if and only if all its inputs are 0. This gate performs the same logic function as an OR gate followed by an inverter. If A and B are two inputs to a NAND gate then output, F of the gate is given as: F = A + BAll the above gates have one output and two or more inputs except the NOT gate, whichhas only one input.PROCEDURE FOR TESTING THE LOGIC GATES IN GIVEN ICs1. Set the power supply to 5V. With the help of a multimeter check the voltage at the output knobs of the power supply.2. Connect wires, long enough to reach the breadboard, with the two knobs of the power supply. Again using multimeter, check voltage at the non-connected end of the wires.3. Insert the 7408 quad 2 input AND gate IC on to the bread board and make supply and ground connections by joining 5V wire to pin # 14 and 0V wire to pin # 7.4. Consult IC’s internal connection diagram for input and output pins of the first AND gate. Connect input pins to logic 0 (0V) and observe the output using LED or logic probe. You can also connect switches at the input lines to facilitate toggling between 1 and 0.5. Try different combinations of logic levels at the two inputs. Again observe the output.6. Repeat the last two steps for all other gates of the same IC. Record the observations.7. Repeat this procedure for all other ICs.OBSERVATIONS Gate Input A Input B Expected Output Observed Output 0 0 0 1 AND 1 0 1 1 0 0 0 1 OR 1 0 1 1 0 - NOT 1 - 0 0 0 1 NAND 1 0 1 1 14
- 13. Logic Design & Switching Theory 1 Lab Session 01NED University of Engineering & Technology – Department of Computer & Information Systems Engineering 0 0 0 1 NOR 1 0 1 1DATA SHEETS Figure 1.1 15
- 14. Logic Design & Switching Theory 1 Lab Session 01NED University of Engineering & Technology – Department of Computer & Information Systems EngineeringGIVEN CIRCUIT Figure 1.2PROCEDURE FOR IMPLEMENTATION OF THE GIVEN CIRCUIT1. Set the power supply.2. Insert ICs on the bread board and make their supply and ground connections.3. As given in the logic diagram, make connections using wires and gates in the ICs.4. Apply different combinations at the three inputs and observe the output.OBSERVATIONSLogic expression for the given logic diagram: __________________________________ A B C Expected Output Observed Output 0 0 0 0 0 1 0 1 0 0 1 1 1 0 0 1 0 1 1 1 0 1 1 1 16
- 15. Logic Design & Switching Theory 1 Lab Session 02NED University of Engineering & Technology – Department of Computer & Information Systems Engineering Lab Session 02OBJECT Working with Electronics WorkbenchELECTRONICS WORKBENCH - EWBElectronics Workbench is a computer aided design tool that provides you with all thecomponents and instruments necessary to create board-level designs. It has completemixed analog and digital simulation and graphical waveform analysis, allowing you todesign your circuit and then analyze it using different simulated instruments and analysisoptions. It is fully integrated and interactive, thus you can change your circuits quickly,allowing fast and repeated what-if analysis.Electronics Workbench provides the following kind of components:• Sources parts bin (AC voltage source, Vcc source, ground, battery, etc)• Basic parts bin (resistors, capacitors, transformers, switches, etc)• Diodes parts bin• Transistors parts bin• Analog ICs parts bin (op-amps, etc)• Mixed ICs parts bin (ADCs, DACs, 555 timers, etc)• Digital ICs parts bin (AND, OR, adders, multiplexers, etc)• Indicators parts bin (voltmeter, ammeter, probe, displays, etc)• Controls parts bin (voltage differentiator, multiplier, etc)• Instruments parts bin (multimeter, oscilloscope, function generator, etc)• Miscellaneous parts bin (write data, textbox, etc) o Write data: This component allows you to save simulation results as an ASCII file. o Text Box: Use this to add descriptive text anywhere in a circuit.ACTIVITYDesign circuit for the logic expression: F = A.B + A.(C.D + B.C )Procedure1. From Logic Gates Parts Bin, Drag and drop the required logic gates on the design area. Use Component Properties dialog box to customize these gates.2. Connect the terminal of these gates according to the given expression. Use additional connectors form the Basic Parts Bin if you want to connect more than wire at a single node.3. Drag and drop a probe from Indicators Parts Bin. Use Component Properties dialog box to customize the color and other properties of the probe. Connect this probe at the output terminal of the circuit to indicate results.4. Select four switches form Basic Parts Bin. Specify the key that controls the switch by typing its name in the Value tab of the Component Properties dialog box. For 17
- 16. Logic Design & Switching Theory 1 Lab Session 02NED University of Engineering & Technology – Department of Computer & Information Systems Engineering example, if you want the switch to close or open when digit ‘1’ is pressed, type 1 in the Value tab, then click OK. Assign different keys to all the switches.5. Connect the output terminals of these switches to each of the four inputs A, B, C and D of the circuit.6. Drag and drop Vcc and Ground form the Sources Parts Bin.7. Connect Vcc terminal to one end and Ground terminal to the other end of all the switches.8. Label the circuit properly using text boxes found in the miscellaneous parts bin.9. Run the circuit using the Activate Simulation switch. Use the keys you have assigned to the switches to toggle them between Vcc and Ground connections, thus providing 1 or 0 respectively to the inputs. Record the results as indicated by the probe for all possible combinations of 1s and 0s at the inputs.EWB Circuit Figure 2.1Observations A B C D Expected Output Observed Output 0 0 0 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 1 0 1 0 1 0 1 1 1 1 0 0 1 1 0 1 1 1 1 0 1 1 1 1 18
- 17. Logic Design & Switching Theory 1 Lab Session 03NED University of Engineering & Technology – Department of Computer & Information Systems Engineering Lab Session 03OBJECT Designing Half and Full Adder Circuits.COMPONENTS AND APPARATUS REQUIRED1. Following ICs and their Datasheets: • 7408 Quad 2-input AND Gate • 7432 Quad 2-input OR Gate • 7486 Quad 2-input XOR Gate2. Digital Trainer DT-01 or the following components: Bread board, 5 V - Power Supply, Multimeter, Logic Probe, LEDs with Resistors, Connecting wires, SwitchesTHEORYHalf AdderA combination circuit that performs the addition of two bits without accounting for theprevious carry is called half adder. It needs two binary inputs and two binary outputs. Theinput variables designate the augend and addend bits. The output variables produce thesum and carry. The simplified sum of product expressions for a half adder are: S = x. y + x. y = x ⊕ y C = x. y Figure 3.1: Circuit diagram for Half Adder 19
- 18. Logic Design & Switching Theory 1 Lab Session 03NED University of Engineering & Technology – Department of Computer & Information Systems EngineeringFull AdderA combinational circuit that performs the addition of three input bits. It consist of three inputsand two outputs. Two of the input variables, represent the two significant bits to be added. Thethird input, represents the carry from the previous lower significant position. The outputvariables produce the sum and carry. The simplified sum of product expressions for a half adderare: S = x. y.z + x. y.z + x. y.z + x. y.z = x ⊕ y ⊕ z C = y.x + x.z + y.z = ( x ⊕ y ).z + x. y Figure 3.2: Circuit diagram for Full AdderIMPLEMENTATION AND OBSERVATIONSImplement the half adder and full adder circuits on a bread board (prepare the pin diagram (useappendix A) and refer to laboratory session 01 for procedure) and record the observations in thefollowing tables: Half Adder Full Adder Inputs Outputs Inputs Outputs x y Carry Sum x y z Carry Sum 0 0 0 0 0 0 1 0 0 1 1 0 0 1 0 1 1 0 1 1 1 0 0 1 0 1 1 1 0 1 1 1 20
- 19. Logic Design & Switching Theory 1 Lab Session 03NED University of Engineering & Technology – Department of Computer & Information Systems Engineering ACTIVITY 1. Simulate half adder circuit using Electronics Workbench. Compare the results of simulation with that of your designed circuit. Attach hardcopy of the output form electronic workbench here. 2. Design a full subtractor circuit and simulate it using Electronics Workbench. Compare the results of simulation with that of your designed circuit. Attach hardcopy of the output form electronic workbench here. 21
- 20. Logic Design & Switching Theory 1 Lab Session 04NED University of Engineering & Technology – Department of Computer & Information Systems Engineering Lab Session 04OBJECT Use of Karnaugh Map (SOP-Expression) method.GIVEN LOGIC EXPRESSION F (A, B, C, D) = ∑ ( 0, 1, 2, 4, 5, 6, 8, 9, 12, 13, 14 )COMPONENTS AND APPARATUS REQUIRED1. Digital ICs and their Datasheets • 7408 Quad 2-input AND Gate • 7432 Quad 2-input OR Gate • 7404 Hex Inverter2. Digital Trainer DT-01 or the following components: Bread board, 5 V - Power Supply, Multimeter, Logic Probe, LEDs with Resistors, Connecting wires, SwitchesPROCEDURE1. Use Karnaugh map to reduce the given function.2. Draw the circuit diagram for the obtained reduced function.3. Implement the reduced circuit using digital ICs on a bread board (prepare the pin diagram (use appendix A) and refer to laboratory session 01 for procedure) and record the observations.REDUCTION OF LOGIC EXPRESSION USING KARNAUGH MAP F CD AB C.D C.D C.D C.D 0 1 3 2 A.B 4 5 7 6 A.B 12 13 15 14 A.B 8 9 11 10 A.BReduced form of the given logic expression is: __________________________________ 22
- 21. Logic Design & Switching Theory 1 Lab Session 04NED University of Engineering & Technology – Department of Computer & Information Systems EngineeringLOGIC DIAGRAM (REDUCED FORM)OBSERVATIONS A B C D Output 0 0 0 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 1 0 1 0 1 0 1 1 1 1 0 0 1 1 0 1 1 1 1 0 1 1 1 1RESULTThe reduced form (SOP Expression) of the given logic function is: ____________________________________________________________The observation table reflects the given logic function. 23
- 22. Logic Design & Switching Theory 1 Lab Session 04NED University of Engineering & Technology – Department of Computer & Information Systems EngineeringACTIVITY 1Using Electronics Workbench, derive a truth table and logic circuit for thefollowing logic expression: F = A + A.BProcedure1. From the Instruments Parts Bin, drag and drop Logic Converter on the design area.2. Double click the Logic Converter to reveal Logic Converter dialog box. This dialog box shows various conversion options between truth table, logic expression and logic circuit.3. Enter the given logic expression in the edit box found at the end of the dialog box. Use ‘ to represent invert of a variable. For example, A is written as A’.4. Click the Boolean Expression to Truth Table button. The truth table appears in the logic converters display.5. Now click the Boolean Expression to Circuit button. This creates the logic circuit for the given expression in the design area. Label the diagram if needed.Resulting Logic CircuitFor the given expression the final circuit will look like: Figure 4.1 24
- 23. Logic Design & Switching Theory 1 Lab Session 04NED University of Engineering & Technology – Department of Computer & Information Systems EngineeringACTIVITY 2Using Electronics Workbench, find a simplified logic expression and circuitfor the following truth table A B C Output 0 0 0 1 0 0 1 1 0 1 0 0 0 1 1 1 1 0 0 0 1 0 1 0 1 1 0 0 1 1 1 1Procedure1. Click three input channels from A to H, across the top of the logic converter. The display area below the terminals fills up with the necessary combinations of ones and zeros to fulfill the input conditions. The values in the output column on the right are initially set to 0.2. Edit the output column to specify the desired output for each input condition. To change an output value, select it and type a new value: 1, 0 or x. An x indicates a don’t care condition.3. To convert this truth table to a Boolean expression, click the Truth Table to Boolean Expression button. The Boolean expression will be displayed at the bottom of the logic converter.4. Simplify the expression by clicking the Simplify button.5. Now click the Boolean Expression to Circuit button. This creates the logic circuit for the given expression in the design area.Resulting Logic CircuitFor the given truth table the final simplified circuit will look like: Figure 4.2 25
- 24. Logic Design & Switching Theory 1 Lab Session 04NED University of Engineering & Technology – Department of Computer & Information Systems EngineeringACTIVITY 3Using Electronics Workbench, find the logic expression and truth table forthe following logic circuit Figure 4.3Procedure1. Attach the input terminals of the logic converter to up to four input points in the circuit.2. Connect the single output of the circuit to the output terminal on the logic converter icon.3. Click the Circuit to Truth Table button. The truth table appears in the logic converters display.4. To convert this truth table to a Boolean expression, click the Truth Table to Boolean Expression button. The Boolean expression will be displayed at the bottom of the logic converter.Resulting Logic ExpressionLogic Expression for the given circuit is found to be: _____________________________ 26
- 25. Logic Design & Switching Theory 1 Lab Session 04NED University of Engineering & Technology – Department of Computer & Information Systems EngineeringFor activities 1, 2 and 3, attach hardcopy of the output (truth table, logic expression andlogic circuit) form electronic workbench here. 27
- 26. Logic Design & Switching Theory 1 Lab Session 05NED University of Engineering & Technology – Department of Computer & Information Systems Engineering Lab Session 05OBJECT Designing a BCD AdderCOMPONENTS AND APPARATUS REQUIRED1. Following ICs and their Datasheets: • 7408 Quad 2-input AND Gate • 7432 Quad 2-input OR Gate • 7483 4-bit Binary Adder2. Digital Trainer DT-01 or the following components: Bread board, 5 V - Power Supply, Multimeter, Logic Probe, LEDs with Resistors (100 Ω), Connecting wires, SwitchesTHEORYA BCD Adder is a combinational circuit that adds two BCD digits in parallel andproduces a sum digit also in BCD. A4 A3 A2 A1 B4 B3 B2 B1 7483-BCD ADDER Cout(C4 ) Z4 Z3 Z2 Z1 Cin(C0) A4 A3 A2 A1 B4 B3 B2 B1 7483-BCD ADDER Cout(C4 ) Z4 Z3 Z2 Z1 Cin(C0) Figure 5.1: BCD Adder Circuit 28
- 27. Logic Design & Switching Theory 1 Lab Session 05NED University of Engineering & Technology – Department of Computer & Information Systems EngineeringA BCD adder must include the correction logic in its internal construction. The two BCDdigits, together with the input carry, are first added using a 4-bit binary adder to producethe binary sum. If no output carry is generated and the binary sum is less than or equal to9, then the corresponding BCD sum is identical, and therefore no conversion is needed.When the output carry is equal to 1, or the binary sum is greater than 9, then a binary0110 is added to the binary sum through another 4-bit binary adder. If Cout is the carryoutput and Z4Z3Z2Z1 is the binary sum form the first 4-bit binary adder, then thefollowing equation indicates the condition when a binary 0110 is to be added: C = COUT + Z4Z2 + Z4Z3IMPLEMENTATION AND OBSERVATIONSImplement the BCD adder circuit according to figure 5.1 on a bread board (prepare thepin diagram (use appendix A) and refer to laboratory session 01 for procedure). A BCDadder has nine input bits (two BCD digits and a carry bit), which can result in a total of512 combinations, of which 312 inputs are don’t care. Since it is a very lengthyprocedure to record results for 200 valid input combinations, therefore for simplicity justrecord results for any eight combinations in the following table: Input BCD Digit 1 BCD Digit 2 Carry BCD Sum Carry A4 A3 A2 A1 B4 B3 B2 B1 Output Z4 Z3 Z2 Z1 29
- 28. Logic Design & Switching Theory 1 lab Session 06NED University of Engineering & Technology – Department of Computer & Information Systems Engineering Lab Session 06OBJECT • Designing of a 4 x 1 Multiplexer • Experimenting with 74150 IC.COMPONENTS AND APPARATUS REQUIRED1. Following ICs and their Datasheets: • 7408 Quad 2-input AND Gates or 7411 Triple 3-input AND Gates • 7432 Quad 2-input OR Gates • 7404 Hex Inverter • 74150 16 x 1 MUX2. Digital Trainer DT-01 or the following components: Bread board, 5 V - Power Supply, Multimeter, Logic Probe, LEDs with Resistors, Connecting wires, SwitchesTHEORYMultiplexersA digital data Multiplexer (MUX) is a combinational circuit having several data inputsand a single output. A set of data-select inputs is used to control which of the data inputsis routed to the single output. A multiplexer is also called a data selector because of thisability to select which data input is connected o the output. Normally there are 2n inputlines and n selection lines whose bit combination determine which input is selected.DESIGN OF A 4 x 1 MULTIPLEXERA 4 x 1 multiplexer is capable of selecting one of four data inputs (see figure 6.1). The 2-bit binary number at the data select inputs, S1 and S0, specifies which of the four datainputs is to be routed to the output. Since there are two data select inputs, therefore theycan select 22 = 4 different data inputs lines. Data-select S0 Inputs S1 Output Data D0 Inputs D1 D2 D3 Figure 6.1: Block Diagram of a 4 x1 Multiplexer 30
- 29. Logic Design & Switching Theory 1 lab Session 06NED University of Engineering & Technology – Department of Computer & Information Systems Engineering Figure 6.2: Circuit Diagram for 4 x 1 MultiplexerImplementation and ObservationsImplement the 4 x 1 Multiplexer circuit (figure 6.2) on a bread board (prepare the pindiagram (use appendix A) and refer to laboratory session 01 for implementationprocedure) and record the observations in the following table. For each data selectcombination, specify the switch number as well as the binary value present on thatselected switch. S1 S0 Output 0 0 0 1 1 0 1 1TESTING OF 74150 - 16 x 1 MUXThe 74150 IC has sixteen data inputs and four data-selection lines. Function of variouspins of this IC is described below:• E0 through E15: Data input lines 31
- 30. Logic Design & Switching Theory 1 lab Session 06NED University of Engineering & Technology – Department of Computer & Information Systems Engineering• A, B, C, D: Data select lines with D being the MSB• W: Active low output line• G’: Active low enable line• VCC and GND: Supply connections linesCircuit Diagram Figure 6.3: Pin connections of 74150 for selecting E0Testing Procedure• Make connections as shown in the circuit diagram.• Apply different data (1 or 0) at data inputs that are labeled as E0 to E15. Only connection for E0 is shown is the figure for simplicity.• Select the data input E0 with the help of data selectors A, B, C, and D.• Observe the output, which shows the complement of the data from E0.• Select all the sixteen data inputs one by one and record your observations in the following table. 32
- 31. Logic Design & Switching Theory 1 lab Session 06NED University of Engineering & Technology – Department of Computer & Information Systems EngineeringObservations G’ D C B A W G’ D C B A W 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 1 0 0 1 0 0 0 1 0 0 1 0 1 0 0 0 0 1 1 0 1 0 1 1 0 0 1 0 0 0 1 1 0 0 0 0 1 0 1 0 1 1 0 1 0 0 1 1 0 0 1 1 1 0 0 0 1 1 1 0 1 1 1 1ACTIVITY1. Consider 4x1 Multiplexer. Draw the output wave-form for the following data inputs (E0, E1, E2, E3,) and select lines A, B (B being the MSB). Output is W. E3 E2 E1 E0 A B W2. Using the 4 x 1 MUX designed in this laboratory session, implement the following logical function: F (A, B, C) = Σ (0,1,4,7) Show your working and input connections in the following block diagram according to the circuit you have implemented. S0 S1 4x1 MUX Output D0 D1 D2 D3 33
- 32. Logic Design & Switching Theory 1 Lab Session 07NED University of Engineering & Technology – Department of Computer & Information Systems Engineering Lab Session 07OBJECT • Designing of a 2 x 4 Decoder / 1 x 4 Demultiplexer • Experimenting with 74138 IC.COMPONENTS AND APPARATUS REQUIRED1. Following ICs and their Datasheets: • 7408 Quad 2-input or 7411 Triple 3-input AND Gates • 7404 Hex Inverter • 74138 3 x 8 Decoder2. Digital Trainer DT-01 or the following components: Bread board, 5 V - Power Supply, Multimeter, Logic Probe, LEDs with Resistors, Connecting wires, SwitchesTHEORYDecoderA Decoder is a combinational circuit that converts binary information form n input linesto a maximum of 2n unique output lines. In practical applications, decoders are often usedfor selecting one of several devices.DemultiplexerA decoder with an enable input can function as a Demultiplexer. A Demultiplexer(DMUX) id a circuit that receives information on a single line and transmits thisinformation on one of 2n possible output lines. The selection of a specific output line iscontrolled by the bit values of n selection lines.DESIGN OF A 2 x 4 DECODER / 1 x 4 DEMULTIPLEXERA 2 x 4 decoder is capable of selecting one of four output lines (see figure 7.1 (a)). The 2-bit binary number at the data inputs, S1 and S0, specifies which of the four data inputs isto be selected. If we add an enable pin and use it as an input line, then this decoder can beconverted to a 1 x 4 Demultiplexer, where S1 and S0 will select a line to which data inputis to be routed (see figure 7.1 (b)). Inputs S0 Select S0 S1 D0 Inputs S1 D0 D1 D1 Enable D2 Data D2 D3 Input D3 (a): Block Diagram of a 2 x 4 Decoder (b): Block Diagram of a 1 x 4 Demulptiplexer Figure 7.1 34
- 33. Logic Design & Switching Theory 1 Lab Session 07NED University of Engineering & Technology – Department of Computer & Information Systems Engineering Figure 7.2: Circuit Diagram for 2 x 4 Decoder / 1 x 4 DemultiplexerImplementation and ObservationsImplement the 2 x 4 Decoder / 1 x 4 Demultiplexer circuit (figure 7.2) on a bread board(prepare the pin diagram (use appendix A) and refer to laboratory session 01 forimplementation procedure) and record the observations in the following table. Enable / Data Input S1 S0 D0 D1 D2 D3 0 0 0 0 0 1 0 1 0 0 1 1 1 0 0 1 0 1 1 1 0 1 1 1TESTING OF 74138 3 x 8 DecoderThe 74138 IC has three inputs and eight output lines. It has three enable inputs and forthe IC to function all three inputs need to be enabled. Function of various pins of this ICis described below: 35
- 34. Logic Design & Switching Theory 1 Lab Session 07NED University of Engineering & Technology – Department of Computer & Information Systems Engineering• Y0 through Y7: Active low data outputs• A, B, C: Input / select lines with C being the MSB• G1: Active high enable Input• G2A’ and G2B’: Active low enable Inputs• VCC and GND: Supply connections linesCircuit Diagram Figure 7.3: Pin connections of 74138Testing Procedure• Make connections as shown in the circuit diagram.• Apply different combinations of 1s and 0s at data inputs.• Observe the output and record your observations in the following table.Observations C B A Y0 Y1 Y2 Y3 Y4 Y5 Y6 Y7 0 0 0 0 0 1 0 1 0 0 1 1 1 0 0 1 0 1 1 1 0 1 1 1 36
- 35. Logic Design & Switching Theory 1 Lab Session 07NED University of Engineering & Technology – Department of Computer & Information Systems EngineeringACTIVITY1. What will be the binary values at the outputs, Y0 through Y7, of 74138 if: • All three enable pins are connected to ground? _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ • All three enable pins are connected to VCC? _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________2. Show connections for 74138 in order to use it as a 1 x 8 Demultiplexer.3. Consider a 2 x 4 Decoder with two enable inputs (one active high - G and one active low – G’). Draw the output wave-forms for D0, D1, D2 and D3, if the two select inputs are A and B (B being the MSB). All outputs are active low. G’ G A B D0 D1 D2 D3 37
- 36. Logic Design & Switching Theory 1 Lab Session 08NED University of Engineering & Technology – Department of Computer & Information Systems Engineering Lab Session 08OBJECT • Designing of a 4 x 2 Priority Encoder • Experimenting with 74148 IC.COMPONENTS AND APPARATUS REQUIRED1. Following ICs and their Datasheets: • 7408 Quad 2-input or 7421 Dual 4-input AND Gates • 7432 Quad 2-input OR Gates • 7404 Hex Inverter • 74148 Encoder2. Digital Trainer DT-01 or the following components: Bread board, 5 V - Power Supply, Multimeter, Logic Probe, LEDs with Resistors, Connecting wires, SwitchesTHEORYEncoderAn Encoder is a digital function that produces a reverse operation from that of a decoder.An Encoder has 2n (or less) input lines and n output lines. The output lines generate thebinary code for the 2n input variables.Priority EncoderA simple encoder may produce an erroneous output if more than one of its inputs is high.A Priority Encoder is one that responds to just one input among those that may besimultaneously high, in accordance with some priority system. The most commonpriority system is based on the relative magnitudes of the inputs: whichever decimal inputis largest is the one that is encoded.DESIGN OF A 4 x 2 Priority EncoderThe following equations represent the outputs of a 4 x 2 priority encoder: A = D 2 + D3 B = D1.D 2 + D3As can be seen from the equations that input D0, which has a binary code 00, is not usedin any equation. A binary code 00 at the output indicates two conditions: Either D0 isselected or no input is selected. In order to differentiate these two conditions, we willprovide an additional output, Z to indicate if at least one of the inputs is a 1. The equationfor Z will be: Z = D1.D 2.D3.D 4If Z is 0, then the binary code 00 at the output indicates that D0 is selected and if Z is 1,then it indicates that no input line is selected. 38
- 37. Logic Design & Switching Theory 1 Lab Session 08NED University of Engineering & Technology – Department of Computer & Information Systems Engineering Figure 8.1: Circuit Diagram for 4 x 2 Priority EncoderImplementation and ObservationsImplement the 4 x 2 Priority Encoder circuit (figure 8.1) on a bread board (prepare thepin diagram (use appendix A) and refer to laboratory session 01 for implementationprocedure) and record the observations in the following table. D3 D2 D1 D0 A B 0 0 0 1 0 0 1 x 0 1 x x 1 x x xTESTING OF 74148 8 x 3 Octal Priority EncoderThe 74148 is a priority encoder with active-Low input for decimal digits. There are nineinputs lines (including an enable input) and five output lines, of which three representsthe binary code for the octal digit. Function of various pins of this IC is described below:• 0 through 7: Active low data inputs representing the octal digits• A2, A1, A0: Active low output lines representing the binary code• E1: Active low enable Input• E0: Active low output indicating none of the inputs is high• GS: Active low output indicating any of the inputs is high• VCC and GND: Supply connections linesTherefore if GS, A2, A1, and A0 are all low, then it shows that line 0 is selected and ifE0, A2, A1, and A0 are all low, then it shows that none of the inputs selected. E0 and GScannot be in the same state provided that E1 is enabled. 39
- 38. Logic Design & Switching Theory 1 Lab Session 08NED University of Engineering & Technology – Department of Computer & Information Systems EngineeringCircuit Diagram Figure 8.2: Pin connections of 74148Testing Procedure• Make connections as shown in the circuit diagram.• Apply different combinations of 1s and 0s at data inputs.• Observe the output and record your observations in the following table.Observations 0 1 2 3 4 5 6 7 A2 A1 A0 GS E0 1 1 1 1 1 1 1 1 x x x x x x x 0 x x x x x x 0 1 x x x x x 0 1 1 x x x x 0 1 1 1 x x x 0 1 1 1 1 x x 0 1 1 1 1 1 x 0 1 1 1 1 1 1 0 1 1 1 1 1 1 1 40
- 39. Logic Design & Switching Theory 1 Lab Session 08NED University of Engineering & Technology – Department of Computer & Information Systems EngineeringACTIVITY1. Cascade the following two 74148 8 x 3 Priority Encoders to form 16 x 4 Priority Encoder. 41
- 40. Logic Design & Switching Theory 1 Lab Session 09NED University of Engineering & Technology – Department of Computer & Information Systems Engineering ` Lab Session 09OBJECT Designing an Odd Parity Generator and Checker for a 3-bit DataCOMPONENTS AND APPARATUS REQUIRED1. Following ICs and their Datasheets: • 7486 Quad 2-input Exclusive-OR Gates • 7404 Hex Inverter2. Digital Trainer DT-01 or the following components: Bread board, 5 V - Power Supply, Multimeter, Logic Probe, LEDs with Resistors, Connecting wires, SwitchesTHEORYParity GeneratorWhen binary data is transmitted and processed, it is – as are all electrical signals –susceptible to noise that can either alter or distort its contents. 1s may be effectively changedto 0s and 0s to 1s. To overcome this problem one or more bits are often added to the data asan aid in detecting errors caused by noise. The most common of these is a Parity bit thatsignifies whether the total number of 1s in a code group is odd or even. In an Odd Paritysystem, the parity bit is made 0 or 1 as necessary to make the total number 1s odd (countingthe parity bit itself). In an Even Parity system, the parity bit is chosen to make the totalnumber of 1s even. Table 9.1 shows how parity bits would be added to BCD code group inboth systems. Decimal BCD Value Parity Bit ABCD Odd Parity Even Parity 0 0000 1 0 1 0001 0 1 2 0010 0 1 3 0011 1 0 4 0100 0 1 5 0101 1 0 6 0110 1 0 7 0111 0 1 8 1000 0 1 9 1001 1 0 Table 9.1: Odd and Even Parity in BCDWhen digital data is received, a parity checking circuit generates an error signal if the totalnumber of 1s is odd in an even parity system or if it is even in an odd parity system. Paritycheck always detects a single error (one bit change from 0 to 1 or 1 to 0) but may not detect 42
- 41. Logic Design & Switching Theory 1 Lab Session 09NED University of Engineering & Technology – Department of Computer & Information Systems Engineering `two or more errors. Odd parity is used more often than even parity because even parity doesnot detect a situation where all 0s are created due to short circuit or other fault condition.DESIGN OF A 3-BIT ODD PARITY GENERATOR AND CHECKERLet x, y, and z be the three bits that constitute the message and are the input to the OddParity Generator Circuit. Since it is an odd parity system, the bit P is generated so as tomake the total number of 1s odd (including P). The function P can be expressed as follows: . . P = x ⊕ y Ο z or P = x Ο y ⊕ zSince the IC available is 7486, which is quad 2input XOR IC, therefore we will convertXNOR also to XOR. . P = x ⊕ y Ο z . P = ( x ⊕ y ) Ο zSince, for even number of variables, ______ XOR = XNORTherefore, ___________ _________ P=(x ⊕y)⊕z = x ⊕y⊕zThis logical expression can be implemented with two XOR gates and an inverter (see figure9.1). Figure 9.1: Circuit Diagram for a 3-bit Parity GeneratorThe 3-bit message and the parity bit are transmitted to their destination, where they areapplied to a Parity Checker Circuit. An error occurs during transmission if the parity of thefour bits received is even, since the binary information transmitted was originally odd. Theoutput C of the parity checker should be a 1 when an error occurs, i.e., when the number of1s in the four inputs is even. Therefore, the function C can be expressed as: . . . C = x Ο y Ο z Ο PUsing the same logic applied for the conversion of the equation of P: C = x⊕ y⊕z⊕PThis logical expression can be implemented with three XOR gates and an inverter (seefigure 9.2). 43
- 42. Logic Design & Switching Theory 1 Lab Session 09NED University of Engineering & Technology – Department of Computer & Information Systems Engineering ` Figure 9.2: Circuit Diagram for a 3-bit Parity CheckerImplementation and ObservationsImplement the 3-bit Parity Generator and Checker circuits (figure 9.1 and 9.2) on a breadboard (prepare the pin diagram (use appendix A) and refer to laboratory session 01 forimplementation procedure) and record the observations in the following table. x y z P x y z P C x y z P C 0 0 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 1 1 0 0 1 0 1 0 0 0 1 0 1 0 1 0 0 1 1 0 0 1 1 1 0 1 1 1 0 0 0 1 0 0 1 1 0 0 1 0 1 0 1 0 1 1 1 0 1 1 1 0 0 1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 1 1 1 Odd Parity Generation Odd Parity CheckACTIVITY1. Try using the parity checker of figure 9.2 as 3-bit parity generator. Write the details here: _______________________________________________________________________ _______________________________________________________________________ _______________________________________________________________________ _______________________________________________________________________ _______________________________________________________________________ _______________________________________________________________________ _______________________________________________________________________ _______________________________________________________________________ 44
- 43. Logic Design & Switching Theory 1 Lab Session 10NED University of Engineering & Technology – Department of Computer & Information Systems Engineering Lab Session 10OBJECT Driving a seven segment display using 7447 / 7448 driver IC.COMPONENTS AND APPARATUS REQUIRED1. Following ICs and their Datasheets: • Seven Segment Displays (Common Anode / Common Cathode) • 7447 / 7448 BCD to Seven Segment Driver2. Digital Trainer DT-01 or the following components: Bread board, 5 V - Power Supply, Multimeter, Logic Probe, LEDs with Resistors, Connecting wires, SwitchesTHEORYSeven Segment Displays A Seven Segment Display consists of seven light-emitting segments. The segments aredesignated by letters a through g (see figure 10.1). By illuminating various combinations ofsegments, the numerals 0 through 9 can be displayed. Seven Segment Displays are commonlyconstructed with light-emitting diodes (LEDs) and with liquid-crystal displays (LCDs). LEDsgenerally provide greater illumination levels but require much greater power than LCDs.An LED display can be a common-anode type or common cathode type. In common anode type,a high voltage is applied at the common terminal of the display and low voltage is applied at asegment’s terminal for illumination. In the common-cathode type, a low voltage is applied at thecommon terminal of the display and high voltage is applied at a segment’s terminal forillumination. a f b g e c d Figure 10.1: Seven Segment Display7447 / 7448 BCD to Seven Segment Driver7447 / 7448 IC is particularly used to drive Seven Segment. Its input is a BCD numberand output drives a seven segment display. 7447 is used to drive common-anode displayswhereas 7448 is used to drive common cathode displays. 7447 / 7448 is a 16 pin IC.Function of various pins of these ICs is described below:• A, B, C, D: Inputs representing BCD digits (D being the MSB). 45
- 44. Logic Design & Switching Theory 1 Lab Session 10NED University of Engineering & Technology – Department of Computer & Information Systems Engineering• OA through OG: Outputs to drive segments a through g of the display. (Active low in 7447 and active high in 7448).• RBI: Ripple Blanking Input. Turns off all the segments if kept low, provided that LT is kept high and all other inputs (A, B, C, D, BI) are kept low. Should be kept high otherwise.• BI / RBO: Wire-AND logic serving as a Blanking Input and / or Ripple Blanking Output. o BI: Turns off all the segments if low. o RBO: Goes to a low level (response condition) along with other outputs, when RBI and inputs A, B, C, and D are low with LT input at high level.• LT: Lamp Test input. Tests whether all segments are working or not. Illuminates all segments if kept low, provided that BI is kept high. Should be kept high otherwise.• VCC and GND: Supply connections linesCIRCUIT DIAGRAM Figure 10.2: Circuit diagram for 7447driving a common-anode displayIMPLEMENTATION AND OBSERVATIONS• Make connections as shown in the circuit diagram (refer to laboratory session 01 for implementation procedure).• Apply different combinations of 1s and 0s at data inputs.• Observe the output and record your observations in the following table. 46
- 45. Logic Design & Switching Theory 1 Lab Session 10NED University of Engineering & Technology – Department of Computer & Information Systems Engineering Decimal BCD Inputs Seven Segment Outputs Digit D C B A a b c d e f g 0 0 0 0 0 1 0 0 0 1 2 0 0 1 0 3 0 0 1 1 4 0 1 0 0 5 0 1 0 1 6 0 1 1 0 7 0 1 1 1 8 1 0 0 0 9 1 0 0 1ACTIVITY1. Perform the Lamp Test for the designed circuit and write your observations. _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________2. How can you use 7447 IC to drive a common-cathode display? _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________3. What symbols appear in the seven segment display if inputs DCBA are: DCBA Symbol 1010 1011 1100 1101 1110 1111 47
- 46. Logic Design & Switching Theory 1 Lab Session 11NED University of Engineering & Technology – Department of Computer & Information Systems Engineering Lab Session 11OBJECT Testing different modes of JK-FFCOMPONENTS AND APPARATUS REQUIRED1. Following ICs and their Datasheets: • 7473 / 7476 JK Flip-Flop2. Digital Trainer DT-01 or the following components: Bread board, 5 V - Power Supply, Multimeter, Logic Probe, LEDs with Resistors, Connecting wires, SwitchesTHEORYFlip-FlopA flip-flop circuit can maintain a binary state indefinitely (as long as the power isdelivered to the circuit) until directed by an input signal to switch states. The majordifferences among various types of flip-flops are in the number of inputs they possess andin the manner in which the inputs affect the binary state.JK Flip-FlopJK flip flop is an edge triggered device. A typical JK flip flop has three inputs: J, K and aclock input. The flip-flop can be either positive or negative edge triggered. The output Qis available in complemented form as well.Beside the usual inputs and output, most of the flip-flop IC also possess twoasynchronous inputs, namely Preset and Clear. These inputs are usually active low. Ifused Preset and Clear inputs keep the flip-flop in set and reset state respectively,irrespective of the other inputs. Both of these inputs cannot be used simultaneously,otherwise they will bring the flip-flop in unstable state. Figure 11.1: Symbol for JK flip-flop (a) positive-edge triggering (b) active low Preset (PR) and Clear (CLR) with positive-edge triggering (c) active low Preset (PR) and Clear (CLR) with negative-edge triggering 48
- 47. Logic Design & Switching Theory 1 Lab Session 11NED University of Engineering & Technology – Department of Computer & Information Systems EngineeringTESTING OF 7473 / 7476 DUAL JK FLIP-FLOPBoth the ICs 7473 and 7476 are similar in functionality except for one difference. Theflip-flops in 7473 have only one type of active low asynchronous input, which is theClear input, whereas the flip-flops in 7476 have both Preset and Clear inputs. Both theseICs have negative edge triggered flip-flops.Circuit Diagram Figure 11.2: Pin connections of 7476Testing Procedure• Make connections as shown in the circuit diagram (figure 11.2).• Apply different combinations of 1s and 0s at J and K inputs.• Observe the output and record your observations in the following table.Observations J Q K 0 0 0 1 1 0 1 1ACTIVITY1. Observe the output, Q of JK flip-flop if the clock input is connected to VCC or GND instead of a clock source. Write your observations here: _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ 49
- 48. Logic Design & Switching Theory 1 Lab Session 12NED University of Engineering & Technology – Department of Computer & Information Systems Engineering Lab Session 12OBJECT Designing sequential circuit for the given state diagram using D flip-flop.GIVEN STATE DIAGRAM 0/0 00 1/1 1/0 0/0 11 01 0/0 1/1 1/0 10 0/0 Figure 12.1: State DiagramCOMPONENTS AND APPARATUS REQUIRED1. Following ICs and their Datasheets: • 7474 D Flip-Flop • ICs of basic gates (AND, OR, NOT, XOR, etc) as required2. Digital Trainer DT-01 or the following components: Bread board, 5 V - Power Supply, Multimeter, Logic Probe, LEDs with Resistors, Connecting wires, SwitchesTHEORYSequential CircuitsIn Sequential Circuits, the output not only depends on the present inputs, but also onprevious states of the circuit. These circuits use memory elements (latches, flip-flops) andthe binary information stored in the memory elements at any given time defines the stateof the sequential circuit.Analysis of a Sequential CircuitThe behavior of a sequential circuit is determined from the inputs, the outputs, and thestates of its flip-flops. Both the outputs and next state are a function of the inputs and the 50
- 49. Logic Design & Switching Theory 1 Lab Session 12NED University of Engineering & Technology – Department of Computer & Information Systems Engineeringpresent state. The analysis of a sequential circuit form a state diagram comprises of thefollowing:• Selecting a particular flip-flop to design the circuit• Obtaining state table from the state diagram• Finding input equations for the selected flip-flop• Finding state equations (not required for the construction of circuit)• Implementing the circuit using selected flip-flops and their input equationsANALYZING THE GIVEN STATE DIAGRAMD Flip-FlopD flip-flop is also called transparent flip-flop as it simply transfers the input data to theoutput. For our design, we require the graphical symbol and excitation table of D flip-flop(see figure 12.2). Qt Qt+1 T 0 0 0 0 1 1 1 0 0 1 1 1 (a): Graphical Symbol (b): Excitation table of D Flip-Flop Figure 12.2Characteristic equation of D flip-flop is: Q(t+1) = DState TableThe given state diagram has four states, so we will need two D flip-flops (FF-0, FF-1).Form state table form the given state diagram and record the results in the followingtable: Present State Input Next State Output Input to Input to Q1t Q0t x Q1(t+1) Q0(t+1) z FF-0, D0 FF-1, D1 51
- 50. Logic Design & Switching Theory 1 Lab Session 12NED University of Engineering & Technology – Department of Computer & Information Systems EngineeringInput EquationsUsing Karnaugh map, the input equations, D0 and D1, for the two flip-flops can be found. D0 D1 Q0x _ _ _ _ Q0x _ _ _ _ Q1 Q0x Q0x Q0x Q 0x Q1 Q0x Q0x Q0x Q0x _ _ Q1 Q1 Q1 Q1 D0 = _________________ D1 = _________________State EquationsUsing the characteristic equation of D flip-flop, we can find the state equations, Q0(t+1)and Q1(t+1), for the to flip flops.Q0(t+1) = _______________________ Q1(t+1) = _______________________ _______________________ _______________________ _______________________ _______________________Circuit Diagram 52
- 51. Logic Design & Switching Theory 1 Lab Session 12NED University of Engineering & Technology – Department of Computer & Information Systems EngineeringImplementation Procedure and Observations1. Implement the circuit using digital ICs on a bread board (prepare the pin diagram (use appendix A) and refer to laboratory session 01 for procedure).2. Make the clear inputs of the flip-flops low (to clear the flip-flops). The flip-flops will remain in clear state as long as the clear inputs are connected to low level.3. Connect output Q0 and the clock pulse to an oscilloscope.4. Apply 0 to the input x.5. Now make the clear inputs to high.6. Observe the waveform for the first 5 clock pulses and record it.7. Repeat steps 2 to 6, keeping x=1 in step 4 this time.8. Repeat steps 2 to 7, this time connecting Q1 instead of Q0 to the oscilloscope in step 3. Record your observations. (Keep frequency of the clock pulse low (e.g.1Hz) so that the output waveforms can be observed easily) 1 2 3 4 5 Clock Pulse Output Waveform for Q0 when x=0 Output Waveform for Q0 when x=1 Output Waveform for Q1 when x=0 Output Waveform for Q1 when x=1 53
- 52. Logic Design & Switching Theory 1 Lab Session 13NED University of Engineering & Technology – Department of Computer & Information Systems Engineering Lab Session 13OBJECT Designing a modulo-5 asynchronous up-counter using JK-FFCOMPONENTS AND APPARATUS REQUIRED1. Following ICs and their Datasheets: • 7400 Quad 2-input or 7410 Triple 3-input NAND Gates • 7476 / 7473 JK Flip-Flop2. Digital Trainer DT-01 or the following components: Bread board, 5 V - Power Supply, Multimeter, Logic Probe, LEDs with Resistors, Connecting wires, SwitchesTHEORYDigital CountersA digital counter is a set of flip-flops whose states change in response to pulses applied atthe input to the counter. The flip-flops are interconnected so that their combined state atany time is the binary equivalent of the total number of pulses that have occurred up tothat time. Every counter resets after a certain number of clock pulses. Thus, as it nameimplies, a counter is used to count pulses. An n stage counter can count up to a maximumof 2n states. n is equal to the number of flip-flops required for the construction of counter.Modulus CountersThe number of input pulses that causes a counter to reset to its initial count is called themodulus of the counter. Thus, the modulus equals to total number of distinct states(counts), including zero that a counter can store. A binary counter with n stages is amodulo-2n (or mod-2n) counter. The largest count a mod-N counter can achieve is N-1, i.e.a mod-N counter never reaches the binary number equal to its modulus. N is always equalto or less than 2n.Counters can be classified as:• Synchronous Counters, which are clock driven. All the flip-flops are driven by a single clock.• Asynchronous Counters, which are event driven. Clock input is given to the first flip-flop only. Rest of the flip-flops are driven by their preceding flip-flops.DESIGN OF A MOD-5 ASYNCHRONOUS UP COUNTERThe number of flip-flops required to construct a mod-5 counter is 3, because 5 should beless than or equal to 2n. This counter will count from 0 to 4, a total of 5 distinct states.Since a 3-stage counter can count up to 8 states at maximum, a NAND gate is used toreset it after 5 clock pulses. Figure 13.1 shows the logic diagram. 54
- 53. Logic Design & Switching Theory 1 Lab Session 13NED University of Engineering & Technology – Department of Computer & Information Systems Engineering Figure 13.1: A Mod-5 Asynchronous Up CounterImplementation and ObservationsImplement the mod-5 counter circuit (figure 13.1) on a bread board (prepare the pindiagram (use appendix A) and refer to laboratory session 01 for implementationprocedure) and record the observations in the following table. Clock Pulse Q2 Q1 Q0 0 1 2 3 4 5 6 7ACTIVITYDraw the timing diagram for mod-5 counter designed in this laboratory session. 55
- 54. Logic Design & Switching Theory 1 Lab Session 14NED University of Engineering & Technology – Department of Computer & Information Systems Engineering Lab Session 14OBJECT Experimenting with 74194 4-bit bidirectional universal shift registerCOMPONENTS AND APPARATUS REQUIRED1. Following ICs and their Datasheets: • 74194 4-bit bidirectional universal shift register2. Digital Trainer DT-01 or the following components: Bread board, 5 V - Power Supply, Multimeter, Logic Probe, LEDs with Resistors, Connecting wires, SwitchesTHEORYShift RegistersA Register is a set of flip-flops used to store binary data. A register, which is capable ofshifting its binary information either to the right or left, is called a shift register. Thelogical configuration of a register consists of a chain of flip-flops connected in cascade,with the output of one flip-flop connected to the input of next flip-flop. All flip-flopsreceive a common clock pulse, which causes the shift from one stage to the next.Bidirectional Shift RegistersA bi-directional shift register is one whose bits can be shifted from left to right or fromright to left.Universal Shift RegistersA universal shift register is a bi-directional register whose input can be in either serial orparallel form and whose output can be in either serial or parallel form.74194 4-BIT BIDIRECTIONAL UNIVERSAL SHIFT REGISTERThe 74194 register provides parallel as well as serial loading in both directions. Functionof various pins of this IC is described below:• A, B, C and D: Active high inputs for parallel loading.• QA, QB, QC and QD: Active high outputs.• S0 and S1: Active high mode control inputs. The following table shows combinations of S1 and S0 to enable various modes. S1 S0 Clock Action 0 0 x No change 0 1 ↑ Shift right 1 0 ↑ Shift left 1 1 ↑ Parallel load↑ shows the rising edge of the clock pulse 56
- 55. Logic Design & Switching Theory 1 Lab Session 14NED University of Engineering & Technology – Department of Computer & Information Systems Engineering• SR: Active high serial input for right shifting.• SL: Active high serial input for left shifting.• CLR: Active low input. Clears all the flip-flops of the register if set to 0, should be kept high otherwise.• CLK: Clock input.• VCC and GND: Supply connections lines.Thus, A, B, C, and D are inputs for parallel loading, whereas SR and SL are inputs forserial loading with right or left shifting respectively. S1 and S0 are used to select theloading mode.Circuit Diagram Figure 14.1: Pin connections of 74194Testing Procedure• Make connections as shown in the circuit diagram.• Observe the output for the input combinations given in the following table. 57
- 56. Logic Design & Switching Theory 1 Lab Session 14NED University of Engineering & Technology – Department of Computer & Information Systems EngineeringObservations S1 S0 SL SR A B C D QA QB QC QD 0 0 0 1 0 0 0 0 0 1 1 0 0 0 0 1 1 0 0 0 0 0 1 0 1 1 0 0 0 0 1 1 0 0 1 1 0 1 0 0 0 1 1 1 0 1 0 1 1 0 1 0 0 1 1 0 1 1 1 0 0 1 1 1 1 1 0 0 1 1 1 1ACTIVITY1. Show connections of 74194 to convert it into a ring counter with right shifting. 58
- 57. Logic Design & Switching Theory 1 Lab Session 15NED University of Engineering & Technology – Department of Computer & Information Systems Engineering Lab Session 15OBJECT Experimenting with 74245 octal bus transceivers using parallel port PC interfacingCOMPONENTS AND APPARATUS REQUIRED1. Parallel Port Connectors (DB-25) with Cable2. Personal Computer with Windows 98 and TurboC Compiler Installed3. Following ICs and their Datasheets: • 74245 Octal Bus Transceivers with 3-State Outputs4. Digital Trainer DT-01 or the following components: Bread board, 5 V - Power Supply, Multimeter, Logic Probe, LEDs with Resistors, Connecting wires, SwitchesTHEORY3-State LogicSometimes it is necessary to isolate one part of circuit from the other part. For thispurpose some TTL ICs are designed with 3-state logic. Such devices have three possibleoutput states: high, low and high impedance. The device can be put into high impedancestate by a control signal applied to an appropriate pin. When such a device is in highimpedance state, there is very high impedance at its output, effectively isolating thedevice from whatever circuitry the output normally drives.74245 Octal Bus TransceiversA bus is any conducting path or set of paths having electrical connections to one or moredevices. 74245 octal bus transceivers are mainly used to control connectivity betweentwo devices or circuits. It also provides direction control for signal flow. Function ofvarious pin of this IC is given below:• A1 through A8: Bus A.• B1 through B8: Bus B.• G΄: Active low enable input. When high, sets all the bus pins to high impedance state.• DIR: Direction control for signal flow. When set to high logic level, transfers bus A data to B bus. When set to low logic level, transfers bus B data to A bus.• VCC and GND: Supply connections lines.Serial and Parallel Port ConnectorsA Parallel Port can consist of only 25 pin port adapter called a DB-25 and a serial portcan consist of either a 25 pin port adapter called a DB-25 or 9 pin adapter called a DB-9port adapter. Whether the port is a 9 pin or 25 pin it can accomplish all of the same tasksthat serial port communications have been designed for. 59
- 58. Logic Design & Switching Theory 1 Lab Session 15NED University of Engineering & Technology – Department of Computer & Information Systems EngineeringEach adapter can be a male type connector with pins or a female type adapter with tinyholes. Generally a PRINTER port (called LPT1) on the back of a computer is female typeadapter and we need to use MALE DB-25 pin cable on it for PRINTER connection or forparallel LAPLINK cable. And a COM port on the back of a computer is male for theserial ports but it may not necessarily be.Parallel Port Connector – DB-25The DB-25 connector (named for its "B"-size "D"-shaped shell and 25 pins) is practicallyubiquitous in the electronics industry. The DB-25 connector is used for a variety ofpurposes. Two common applications are RS-232/EIA-232 (serial) connections, and theparallel printer interface on the IBM PC. The DB-25 connector is also used for SCSIconnections.Normally the parallel port is used for output to a printer or other device. It sends data 8-bits or one byte at a time in parallel. The other lines available on the DB-25 connector area combination of status lines, control lines, and ground lines. The status and control linesare used for handshaking, commands, and feedback when we are talking to a printer. Figure 15.1: DB-25 Male Figure 15.2: DB-25 Female Figure 15.3: Pin Layout for DB-25As can be seen form figure 15.3, there are four types of pins in this connector:• Data pins (8 pins - D0 to D7): Active high bidirectional lines. 60

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