IGNOU BCA Study-WHAT IS LOGIC GATES CIRCUIT SIMULATION PROGRAM

WHAT IS LOGIC GATES CIRCUIT SIMULATION PROGRAM

This program has been developed by "Alun Davies" as a simple window application
primarily for Windows 3.1 but works mostly under Windows 95 and later. This was

     

freely downloaded from the Website: www.pontybrenin.freeserve.co.uk/ logic/. If you
	have any comments or ideas for future enhancements of the software then please send
them at the e-mail given on the Website.
You need to download the file logic zip and install it at your computer. On execution a
simple screen appears having a two-menu option: File and Help. Select the "New
Project" option of the File Menu to get the project window abeled "Logic Gates
Construction" having a grid on the screen. It also includes a Gate and Connection Tool
Bar. (Please refer to the Figure) In this package, a lot of projects and circuits are given, so if you want to study the functionality of any given circuit, please open it from the file menu. On right click of the circuit you will get options: Where Test Circuit is find that circuit having any error or not, if not you can proceed in execution of the circuit. Like in the given in Figure we have chosen MULTIPLEX.CRC from the projects. On clicking Execute circuit it displays the Truth table of circuit. Please note that this Package cannot be used for making SEQUENTIAL Circuits, those can be made and tested on paper. MAKING A LOGIC CIRCUIT USING LOGIC Let us try to create the logic circuit given in the Figure using LOGIC: To create a logic circuit as above you need to perform the following steps: Step 1:     Create a new project using "File/ New Project" Menu options. Step 2:     Locate find AND gate symbol in the toolbox. Step 3:     Click on the AND gate button. Step 4:     Place the AND gate at desired locations by just clicking at that location. Step 5:     Similarly place OR gate on the desired location. Note: (1) You can place as many gates as you like by just selecting and then clicking on screen. (2) To delete any extra Gate Object, Right Click on that Object and select "Delete" from the menu that will get displayed. (3) If you want to change the position of any gate then first deselect the Gate button on the tool bar by clicking on the selected button again. Now click on the desired object whose position you want to change and drag the pointer wherever you want to place it. Step 6:     Now add labels input 'a' 'b' 'c' 'd' and 'e' by first clicking on                the label button of the tool bar. The names are given as                      you place the label on the project grid through the text                         dialog box. Step 7:      Linking Gates: To link a label and a gate (or gate to                    gate) select "Link" button from the toolbar. Press and                      hold mouse on the source gate/label and move the                      mouse to the destination connection object and release                  the mouse button.               A line should appear. You can remove a connection by                 selecting the Break connection button on the toolbar. Step 8:        Testing a Circuit : Once you have made all the                              connections test your circuit for correctness by pressing                    the Test button on the toolbar. Step 9:         Executing a Circuit : If testing is successful then                           execute the circuit to get the truth table. You can do it by                    selecting Execute button, which is labelled as a truth table                 in the tool bar. Step 10:    Saving the Project : Select File/ Save Project option to                 save with a suitable name with CRC for future use.   A REVISIT OF STEPS OF LOGIC CIRCUIT DESIGN The MCS 012 course has discussed in detail about the procedure of making logic circuits. However, let us revisit the process. This design procedure results in a reliable and economical combinational logic circuit, if correctly applied. Whenever, you design a digital circuit you should follow the systematic steps given below for efficient design and write all the steps in your file. 1.            Write precise circuit specification you understand. 2.            Develop truth table on paper for circuit. 3.            Identify the minterms corresponding to each row in the table. 4.      Draw Karnaugh maps & forming groups of 1's on the Karnaugh map.  Digital Logic Circuits 5.            Write the reduced expression. 6.            Convert the reduced expression into a realizable expression. 7.            Draw the circuit diagram using software. 8.            Test the Digital Circuits using given software. A Complete Example One of our objectives is that you should be able to design your very own combinational logic circuit. Here we are explaining you one example of Full Adder circuit. Step 1: Write precise circuit specification you understand Full-adder is a combinational circuit that forms the arithmetic sum of 3 input bits. Let us assume the 3 inputs are a1, a2, a3 and 2 outputs are S, C. Inputs:        3 input bits to be added (A1, A2, A3) Outputs:     Two output bits ( S (sum bit) ,  C (carry bit) ) Step 2: Development of a truth table on paper for circuit Step 3: Identifying the minterms corresponding to each row in the table S = F1 (1,2,4,7) C = F2 (3,5,6,7) Step 4: Draw Karnaugh maps & forming groups of 1's on the Karnaugh map Step 5: Write the reduced expression S= A1 A2  A3 + A1  A2  A3 + A1  A2  A3 + A1  A2  A3 C= A1  A2 + A1  A3 + A2  A3 Step 6: Convert the reduced expression into a realizable expression S= A1 A2 A3 + A1 A2 A3 + A1 A2 A3 + A1 A2 A3 S= A1 "A2 A3 + A2 A3 # + A1 "A2 A3 + A2  A3 # S= A1 XOR A2 XOR A3 (Refer to de Morgan's theorem) C= A1 A2 + A1 A3 + A2 A3 C= A2 A3 + A1 "A2 XOR A3 # Step 7: Draw the circuit diagram using software Step 8: Test the Digital Circuits using given software Some Additional Tips                                                                                                                         !      Highlighting Inputs and Outputs: In a complex circuit, you would like to         highlight the connections. You can do it by selecting show output () or           show input () buttons. The output is shown in red colour and input is             shown in blue colour. !       Editing Circuits: You can use options for copy, paste, or reposition gates etc. !       Printing Circuits and Truth Tables: To print a logic circuit or a truth table       simply select the window containing the data and then select "File /                 Print...",    option. !       Clocks are not used for any purpose in the circuit at present. !       Sample Circuits are available, use them for better understanding. Trouble Shooting Tips Trouble Probable Solution Circuit cannot be executed. The circuit may be incorrect. Please check connections are made in right direction. This can be checked through right clicking on a gate for selecting the statistics button. Circuit or Truth Table does Ensure proper printer is set up and check printer to be not print. online. On some high-resolution printers circuits and truth tables will be printed smaller. Clock does not work when The clock is not there for execution purposes. It is not circuit is executed. supported by this version of "Logic Gates." File does not load. Please check that the file you are trying to load is a valid ".CRC" file and it exists. File cannot be saved. Check for the storage device, whether full? Tool Box does not appear. It has probably been closed. To open it again select "Window / Show" Menu option. SESSION WISE PROBLEMS We have allotted two practical sessions for you to draw the circuits using Logic Software. You must only draw the combinational circuits using this package, as it is not capable of drawing the sequential circuits. Design the following digital circuits and make a document in the file including all the steps defined in sub-section 1.3. You must come prepared with your design of the following problems on paper in order to take maximum advantage of the Lab session. We hope that with a little design preparation, you will be gaining a lot in these two sessions. Session 1: 1.      Design and implement the Exclusive-OR gate using AND, OR & NOT gates. 2.      Design an "Alarm circuit" using only OR gate in which, if 'doors' OR 'windows' OR 'fire alarm' is         activated, and then alarm sound should start.     (Hint: Alarm is sounded if the output of the above circuit is 1. The Output will be 1 only if any of        the OR conditions given above is true.) 3.     We know NAND gate is universal gate but we need proof, so Design other gates like NOT, OR,          AND & NOR using only NAND gates which will prove that NAND is universal gate. 4.      Design a digital circuit whose output is equal to 1 if the majority of inputs are 1's. The output        is 0 otherwise. 5.      Design the following digital circuit. i)            Half Adder ii)          Half Subtractor iii)        Full Subtractor 6.      Design a logical circuit that will calculate the following function: Inputs Output A B C D 0 0 0 0 0 0 1 1 0 1 0 0 0 1 1 1 1 0 0 1 1 0 1 0 1 1 0 1 1 1 1 1 Explain why your circuit is correct 7.      Design a combinational circuit that takes a 3-bit number and the output of that circuit should be      the square of the input Number. 8.      Design a combinational circuit where input is a 4 bit number and whose output is the 2's                   complement of the input number. 9.      Design the Encoder Circuit, which will convert decimal number to binary number. Session 2: 10.  Design Sequential Circuit, of clocked RS flip flop with 4 NAND gates.     11.  Design Sequential Circuit of clocked D flip flop with AND and NOR gates       12. Design a 8-bit counter using two 4-bit counters.   13.   Design Linear Feed-Back Shift Register. 14.   Design a logical circuit that will calculate the less-than (<) function for         two 2-bit inputs. That is, if the inputs are A and B, each of whose               values can be in the range 0-3 (i.e., 00-11 in binary), then the output         should be 1 whenever A < B, and 0 otherwise. This circuit requires             four inputs, referred to as a1, a2, b1, and b2. a1 and a2 represent a         2-bit number, as do b1 and b2. The output will be true if the decimal           number represented by the pair a1a2 is less than the decimal number       represented by b1b2. Design this circuit with an optimal number of             gates. 15.   A multiplexer circuit accepts N inputs and outputs the value of one of those inputs.      The selection of which input goes out on the output is determined         by a set of M control inputs. A multiplexer with M control inputs can       steer up to 2M inputs to a single output. Design 2-to-1 multiplexer. 16.   A decoder has M inputs and up to 2M outputs. If the logic values on        the M inputs are interpreted as a binary number of value P, then the         Pth output will be at logic 1 while all the others are at logic 0. Design 2-       to-4 decoder.