es4_lab1 - Tufts University School of Engineering...

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Tufts University School of Engineering Department of Electrical and Computer Engineering ES4 - Introduction to Digital Circuits Spring 2008 Lab Section: Tuesday 3:00-6:00pm Experiment 1 Introduction to Breadboard Prototypes Name: Teddy Portney [email protected] Submitted to: James Pringle Experiment Performed: February 5, 2008 Experiment Due: February 7, 2008
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I. PURPOSE The purpose of this lab experiment was to serve as an introduction to physical logic gates, used in this lab in the form of integrated circuit chips. This experiment served as an introduction to equipment used for testing these integrated circuits, a rather complicated-looking circuit with various switches, light bulbs, and wire connections. This lab also introduced a program, Xilinx ISE, and along with that a hardware description programming language, VHDL. I. INTRODUCTION Logic gates are the basis of the heart of a computer, the processor, as well as most other computer components. These gates are specific circuit elements, consisting mostly of transistors. These elements perform all kinds of Boolean functions when arranged correctly. Logic gates only function with Boolean inputs. They work on the idea that each input can only assume one of two possible values, a yes or a no, 1 or 0, true or false, high or low, etcetera, depending on the context of the problem. Usually, in the basic schematic of a logic gate, only a finite number of inputs and outputs are shown. For example, in the logic gates shown in figure 1 of the Appendix section of this report, each logic gate shows two inputs and one output. In the physical implementation, however, there must be connections to each of an eternal voltage source and ground, so that the logic gate can increase or decrease the current traversing the gate to the output according to the function it serves. Simple and complex circuits can both be modeled by forming a truth table, or a chart showing the Boolean input variables, never more than three in this lab, as well as the Boolean outputs of the resultant combination of logic gates. All the truth tables formed in this lab were fairly simple, the most complex of which used three Boolean variables and three logic gates. The inputs of a truth table are determined by first counting the number of Boolean variables present at the input. From this, it is easy to calculate the total number of possible values for the inputs, using the fact that the number of rows in a truth table is equal to 2 n , where n is the number of Boolean input variables. Therefore, if A and B are Boolean input variables, there will be four total possible combinations, and four rows in a truth table for a Boolean function of A and B. Physically, these logic gates appear as integrated circuit (IC) chips, usually with
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es4_lab1 - Tufts University School of Engineering...

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