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 viceversa. 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  2input AND Gate (7408)
1  2input 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. 21a,
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. 21b.
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. 21 2—1 ...
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 Fall '05
 Myer,B

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