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# Lab2_2 - OrCAD Logic Simulation - THE HONG KONG UNIVERSITY...

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Page 1 of 12 THE HONG KONG UNIVERSITY OF SCIENCE AND TECHNOLOGY Department of Electronic and Computer Engineering ELEC 151 Laboratory 2-2 OrCAD Logic Simulation Grading square4 This lab accounts for 3% of your overall grade. A) Objectives: 1. To learn how to use a Circuit Simulator (OrCAD PSpice A/D) to test circuit design. 2. To study the flow of circuit simulation using the Adder-Subtractor circuit captured in Lab 2-1. 3. To design and simulate a Magnitud Comparator based on the Adder–Subtractor circuit used in Lab 2-1. B) Pre-lab Assignments: 1. Read through this lab outline and the summary sheet. 2. Based on the Adder–Subtractor circuit used in Lab 2-1, design a Magnitud Comparator circuit that compares the two 4-bit binary numbers A and B. The circuit must provide 3 outputs: x, y and z. If A=B, then the output x=1. If A<B, then the output y=1. If A>B, then the output z will become 1. Note that only one of the outputs will become 1 at a time. Tips: For details about how to design the circuit, you can read Section 4.8 of the course textbook (4th edition). 3. Follow the same procedures used in Lab 2-1 to create the circuit schematics and generate the netlist files for your “Magnitud Comparator”. Remember to use a new project name for this circuit and save all the files on a diskette. You will have to load the project into the computer and show the schematic to the TA at the beginning of this lab session. C) Experiment Procedures: C1. Introduction After designing a circuit and entering the schematics, how can you know that the design is correct or you have entered everything correctly? In the past, people used to build the circuit using hardware prototype to test it. However, this method of testing has disadvantages such as: The possibility of errors introduced by connecting a wire to a wrong location. Wiring up a circuit is time consuming especially when the design is usually complex in real life applications. The difficulty in probing a single wire in a large array of wires. Circuit simulation provides a method of predicting circuit performance, which is more effective, less costly, and less time-consuming than building hardware prototypes. NOTE : If a design works during simulation, it does NOT necessarily work in real hardware, although the chance is much higher. The reasons are: Your test vectors may not provide sufficient coverage of all the different cases. Simulation is limited by the accuracy of simulation models. E.g., if the simulation model of a gate has 0ns delay, it is unrealistic to assume that 10 levels of gates will have the same delay.

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Page 2 of 12 In the previous lab, you have prepared the design for simulation by choosing the " Analog or Mixed Signal Circuit Wizard " when creating the project at the beginning. OrCAD Capture generates a circuit file set containing the circuit netlist and analysis commands , which are read by PSpice A/D for simulation. It then formulates the file set into meaningful graphical plots, which can be marked for display from the SCHEMATIC page. The output appears is much the same way that it would appear
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Lab2_2 - OrCAD Logic Simulation - THE HONG KONG UNIVERSITY...

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