Contains material © Digilent, Inc. 11 pages Lab #1 Truth Tables, ICs, and Breadboards Revised 1_25_10 The three primary logic relationships, AND, OR, and NOT (or inversion) can be used to express any logical relationship between any number of variables. These simple logic functions form the basis for all digital electronic devices – from a simple microwave oven controller to a desktop PC. We can write logic equations of the form "F = A AND B" that use these three relationships to specify the behavior of any given digital system. Pause a moment and think about this: any digital system, up to and including a highly complex computer system, can be built entirely of devices that do no more than implement these three simple functions. As engineers, we must address two primary concerns: how to express a given requirement or problem statement in terms of these simple logic relationships; and how to build electronic devices (or circuits) that can be used to implement these relationships in real devices. This lab will begin to explore the second of these questions – how to arrange switching devices so that these relationships are realized. After completing this module, you should… -Be familiar with truth tables, understanding the row ordering used in ECE3714. - now the truth-table definitions of AND,OR, NOT, NAND, NOR, XOR, and XNOR (or EQV) logic relationships; -Understand how switching circuits can be used to implement basic logic functions;  - Be able to sketch a logic circuit from a logic equation, and be able to read a logic equation from a circuit. - Be able to create a logic circuit from a truth table definition; - Be able to construct a basic logic circuit on the breadboard, including the appropriate connection of power, ground, and signal pins. This module requires: -A solderless breadboard -The Digital chip kitLab #1 Truth Tables, ICs, and Breadboards Contains material © Digilent, Inc. 2 Truth Tables Logic equations are used to show how an output logic signal should be driven in response to changes on one or more input signals. The equal sign (“=”) is typically used as an assignment operator to indicate how information should flow through a logic circuit. For example, the simple logic equation “F = A” specifies that the output signal F should be assigned whatever voltage is currently on signal A. Note this does not imply that F and A are the same circuit node – in fact, the use of a logic equation to specify circuit behavior implies that the inputs and outputs (in the case, F and A) are separated by a circuit component. In digital circuits, circuit components act like one-way gates. Thus, the logic equation “F = A” dictates that a change on the signal A will result in a change on the signal F, but a change on F will not result in a change on A. Most useful logic equations specify an output signal that is some function of input signals. For example, the logic equation “F = A and B” specifies a logic circuit whose output will be driven to a high voltage only when both inputs are driven to a high voltage. Below are six common logical functions written as conventional logic equations. The AND relationship, F = AB, can be written without an operator between the A and B (but more properly, a dot () should be placed between the variables to make the relationship clear). The OR relationship uses the plus sign, and the NOT or inversion relationship is shown by placing a bar over the inverted variable or by placing a single quote character after the variable or quantity to be inverted (two possible notations are shown for several relationships). AND OR XOR NOT NAND NOR F=A‟B + AB‟ Compound logic expressions can be built from these basic functions. For example, an output might be driven to a high voltage if input signals A and B are both at a high voltage, or if input C is a low voltage, or if C is a high voltage at the same time that A is a low voltage. This relationship can be concisely written as “F = (AB + C’) + A’C .” A truth table is the primary tool for capturing logical relationships in a concise and universally understood format. All possible combinations of inputs are shown in rows on the left of a truth table. A truth table with N inputs requires 2N rows to list all possible input combinations. A „0‟ or „1‟ in the rightmost column indicates whether the logical relationship evaluates to a “true” for the combination of inputs shown in the adjacent row. For example, a truth table with two inputs, A and B, will require 22, or 4 rows to list all possible combinations: “0 0”, “0 1”, “1 0”, and “1 1”. For the ANDing operation, the output is “true” only when both inputs are true, so the rightmost column would have a „1‟ only in the last row. For “F = A’ and B”, the truth table would have a „1‟ only in the second row. Problem 1: Complete the truth tables in the lab exercise pages for the basic logic functions shown on the datasheet.Lab #1 Truth Tables, ICs, and Breadboards Contains material © Digilent, Inc. 3 Integrated Circuits (or “chips”) and chip packaging The terms chip and integrated circuit refer to circuits using microscopic transistors that are all co-located on the same small piece of silicon. Chips have been designed to do all sorts of functions, from very simple and basic logical switching functions to highly complex processing functions. Some chips contain just a handful of transistors, while others contain several million transistors. Some of the longest-surviving chips perform the most basic functions. These chips, denoted with the standard part numbers "74XXX", are simple small-scale integration (SSI) devices that house small collections of logic circuits. For example, a chip known as a 7400 contains four individual NAND gates, with each input and output available at an external pin. As shown in the figures below, the chips themselves are much smaller than their packages. During manufacturing, the small, fragile chips are glued (using epoxy) onto the bottom half of the package, bond-wires are attached to the chip and to the externally available pins, and then the top half of the chip package is permanently affixed. Smaller chips may only have a few pins, but larger chips can have more than 500 pins. Since the chips themselves are on the order of a