23 October – Day 17
Wassn7 due
Chapter 13 – (goes together well with chapter 3)
Read first page and a half
note: talking about the CU of a CPU
A multiplexer is a device which accepts multiple inputs and produces a
single output. Simple example: an AND gate
Think of figure 13.1 as a “black box” which behaves as specified in the
truth table.
What should the black box do? (what’s it function?) Specify via truth
table.
Note that input “s” is a select input. If s is a 0, then the value of x0 is
passed to the output, f. If s is a 1, then the value of x1 is passed to the
output f.
Q: How do I construct the circuit which performs f (what’s inside the
black box?) Remember that the circuit is some combination of gates
(and, or, not, etc)
The Boolean function f can be defined by a Boolean expression
Q: How do I create a Boolean expression
To create the Boolean expression,
0.) Generate the truth table (given in example) – may have to test the
black box and determine outputs if not given!
1.) at each row where f = 1, create a product (and) of terms. That is,
for each term with a 1 value, use it directly; if the term has a 0 value,
use its complement (not)
2.) sum (or) all of the products together from step 1
Example 13.1
step 1.)
Row 3 = S’ X0 X1’
Row 4 = S’ X0 X1
CSC 490 Course Notes and Outline, © Dr. Gary Locklair, Fall 2006
