Transcript Logic Gates - KSU Web Home

CS 3501 - Chapter 3 (3A and 10.2.2)
Part 3 of 8
Dr. Clincy
Professor of CS
Will Review Exam 1
Dr. Clincy
Lecture
Slide 1
Logic Gates
• We have looked at Boolean functions in abstract
terms.
• In this section, we see that Boolean functions are
implemented in digital computer circuits called gates.
• A gate is an electronic device that produces a result
based on two or more input values.
– In reality, gates consist of one to six transistors, but digital
designers think of them as a single unit.
– Integrated circuits contain collections of gates suited to a
particular purpose.
Dr. Clincy
Lecture
2
Logic Gates
• The three simplest gates are the AND, OR, and NOT
gates.
• They correspond directly to their respective Boolean
operations, as you can see by their truth tables.
Dr. Clincy
Lecture
3
Logic Gates
• Another very useful gate is the exclusive OR (XOR)
gate.
• The output of the XOR operation is true only when the
values of the inputs differ.
Note the special symbol 
for the XOR operation.
Dr. Clincy
Lecture
4
Logic Gates
• NAND and NOR
are two very
important gates.
Their symbols and
truth tables are
shown at the right.
Dr. Clincy
Lecture
5
Logic Gates
• NAND and NOR
are known as
universal gates
because they are
inexpensive to
manufacture and
any Boolean
function can be
constructed using
only NAND or only
NOR gates.
Dr. Clincy
Lecture
6
Logic Gates
• Gates can have multiple inputs and more than
one output.
– A second output can be provided for the
complement of the operation.
– We’ll see more of this later.
Dr. Clincy
Lecture
7
Combinational Circuits
• We have designed a circuit that implements the
Boolean function:
• This circuit is an example of a combinational logic
circuit.
• Combinational logic circuits produce a specified output
(almost) at the instant when input values are applied.
– In a later section, we will explore circuits where this is not the
case (sequential circuits).
Dr. Clincy
Lecture
8
Combinational Circuits
• We have designed a circuit that implements the
Boolean function:
• This circuit is an example of a combinational logic
circuit.
• Combinational logic circuits produce a specified output
(almost) at the instant when input values are applied.
– In a later section, we will explore circuits where this is not the
case (sequential circuits).
Dr. Clincy
Lecture
9
CS3501 Exam 1 Results
REMINDERS:
• Per the course intro, the Professor has absolutely NO control of your final
grades – Professor doesn’t control the score average, score deviation or
grading scale for each exam
• Per the course intro, your grades are relative and not absolute – your grade is
relative to your classmates (and not on some scale set by the Prof)
• Per the course intro, everyone is graded using the same “standards” and
“rubric” and as a result, your scores are relative.
Average Score = 33 (Average Grade = 75)
Score Standard Deviation = 18 (Very large)
Grading Scaled Used:
• 78-61 A-grade (6 students)
• 60-43 B-grade (14 students)
• 42-25 C-grade (26 students)
• 24-7 D-grade (18 students)
• 6-0 F-grade (5 students)
Dr. Clincy
10