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Electronic Labs_66

# Electronic Labs_66 - Laboratory Exercise 2 AND/OR LOGIC...

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Unformatted text preview: Laboratory Exercise 2 AND/OR LOGIC GATES; Performance Objectives A. Identify and demonstrate the digital logic AND gate and verify its logic function. B. Identify and demonstrate the digital logic OR gate and verify its logic function. C. Identify and demonstrate the digital logic NOT circuit (INVERTER) and verify its logic function. D. Demonstrate how, using INVERTERS, an AND gate can be made to function as an OR gate and vice versa. Basic Concepts 1. In a positive logic system, the HI level, or state is assigned the number 1. The L0 level is assigned the number 0. 2. A logic gate is the electronic equivalent of an electromechanical switch. 3. The logic AND gate is the equivalent of switches in series. Only when all switches (inputs) are closed (1 logic level) does current flow (output = 1). 4. The logic OR gate is the equivalent of switches in parallel. If any one or com- bination of switches is closed (1 logic level) current flows (output = 1). 5. The NOT circuit inverts a logic level so that a 1 input will become a 0 output and vice-versa. 6. AND and OR gates can be made using OR and AND gates, respectively, by using INVERTERS at the gate inputs and out- puts. Introductory Information In the previous lesson we stated that there are only two states (voltage levels) in a binary system. These states are referred to as the H1 and LO states and in a positive logic system that is used on this trainer, a HI = +2.0 to 5V and L0 = 0 to 0.4V. We also assign numbers to the logic states. In a positive logic system then, a H1 is the logic 1 state and a L0 is the logic 0 state. The logic gate is the basic building block of any digital system. There are three basic logic circuits. They are the AND gate, the OR gate, and the NOT NOT CIRCUIT circuit (INVERTER). All other logic circuits can be obtained from these basic logic circuits. Additional Reading See the bibliography at the back of this manual for additional reading material related to basic logic concepts and gates. Equipment and Materials The Model A818145 Digital Logic Trainer with: 3 - Hex Inverter (7404) 1 - 2-input AND Gate (7408) 1 - 2-input OR Gate (7432) 1 - LED Display 2 - Switches Objective A. Identify and demonstrate the digital logic AND gate and verify its logic function. Preparatory Information. A logic gate is the elec- tronic equivalent of one or more switches that permit a signal to pass when the switch circuit is complete and not to pass when the switch circuit is not complete. The AND gate, shown in Fig. 2-1a, has two inputs. When one or both inputs are L0 (logic 0) the output will be LO. Only when both inputs are HI (logic 1) will the output be HI. We can say that it operates in the same manner as two switches in series, as shown in Fig. 2-1b. Only when switches SA and SB are closed (1 position) will the lamp light (1). In the two circuits shown then, it can be said that only when inputs A AND B are HI will the output (Y) be HI, hence the name AND gate. If either A INPUTS { B :D-—Y 2 AB} OUTPUT fa} 0 D S A 01 0/5“ I 'I= LIT ‘f 0— UNLJT (b) Fig. 2-1 2—1 ...
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