Unformatted text preview: Laboratory Exercise 2 7 SIM ULA TING PROBLEMS
WITH LOGIC CIRCUITS Performance Objectives A. Discuss the technique for designing a com
binationlogic decision making circuit and
implement the circuit to verify the results. B. Use Boolean simplification techniques to
design, implement, and verify A VOTE
SYSTEM that will indicate a majority
“YES”, majority “NO”, and a “TIE”
vote. Basic Concepts 1. Problem simulation with combinationlogic
circuits requires that all variables first be
determined and identiﬁed. 2. A truth table is then constructed which
includes all variables, all possible state
combinations of these variables, and the
desired output conditions for these com
binations. 3. A Boolean equation can then be written
for each variable necessary to simulate
the problem. 4. Boolean equation simplification techniques
can then be utilized to allow implemen
tation of a simpler logic circuit configur
ation. 5. The logic circuit can then be constructed
from the simplified Boolean equation. Introductory Information In this Laboratory Exercise we will discuss the
technique of designing combinationlogic circuits
to simulate real problems. Although the problems
presented in this Laboratory Exercise are compara
tively simple, the technique used to simulate them
could apply as easily to more compex problems.
The logic circuit solution, of course, may also be
more complex. The use of combinationlogic cir—
cuits in problem simulation affords the user the
opportunity of working with circuit inputs he
can control, observing circuit outputs that are the
result of known inputs, and realizing circuit
solutions applicable to the real problem without
the necessity of manipulating or controlling real
variables. Additional Reading See bibliography at the back of this manual for
additional reading material related to simulating
problems with combinationlogic circuits and logic
simplification techniques. Review Laboratory Exer
cise 26 on Boolean algebra, identities, laws, and
theorems. Equipment and Materials The Model ASl8145 Digital Logic Trainer with:
 4input NAND Gates (7420)  2input AND Gates (7408)  2input OR Gates (7432) 2input NAND Gates (7400)  2input NOR Gates (7402)  Hex Inverters (7404)  Switches  LED Displays cornmcoihupmun Objective A. Discuss the technique for designing
a combinationlogic decision making circuit and
implement the circuit to verify the results. Preparatory Information. Simulation of a prob
lem with combinationlogic circuitry requires a
series of operations as discussed in the basic con
cepts. To illustrate the technique, we will simulate
the problem of the farmer, the hen, the fox,
and the corn. The problem is that the farmer
wants to get to the other side of a river with the
hen, fox, and corn all intact. Ordinarily this
would not be a problem but the farmer notices
that the only boat available is very small; it can
only hold himself and any one of the items at a
time. If he leaves the hen and the corn, the hen will
eat the corn. If he leaves the fox and the hen, the
fox will eat the hen. TheSe same restrictions apply
when the farmer has to leave more than one item
on the other side of the river after each crossing. The first step in our simulation is to identify each
input variable, the desired number of output
conditions,and assign letter designations to them.
The letter designations are arbitrary. Hence, we
will let the farmer be A, the hen will be B, the
fox will be C, and the corn will be D. We can 2 71 ...
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 Fall '05
 Myer,B

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