Computer Science
Topic 3. Fundamentals of
Logic Circuit Design
1)Introduction to Logic Design:
Logic Gates
● Logic gates are the basic building blocks that all of logic is built up
from.
● It is important to be familiar with which logic gates are which, their
appearance and how they work.
Truth Tables and Logic Circuits
● Truth tables are a way of writing down what a circuit does.
● Logic circuits are a way of visualizing how to connect up the gates
to do the truth table.
,Karnaugh Maps
● Karnaugh maps are a way to convert truth tables into efficient logic
circuits.
● Computers are better than humans at this task, so not much time
will be spent on it.
Important Logic Blocks
● This is the level of complexity that should be focused on for logic
design.
● When talking about how the processor is built, these kinds of logic
blocks will be used.
Memory Arrays
● Logic blocks can be put together to build a memory array.
Counter
● A counter needs to keep track of the current count, which is its
state, and also needs a clock to determine how fast it counts.
● This is the same clock that determines how fast a processor runs.
, 2)Basic Logic Gates:
What are logic gates?
● Logic gates are the smallest unit of logic circuits used to build up
logic.
● They are the basic stuff used when constructing logic circuits.
● The standard basic gates are the not gate (inverts the input), and
gate (true if both inputs are true), or gate (true if either input is
true), NAND gate (not a and b), XOR gate (true if inputs are
different), and XNOR gate (true if inputs are the same).
Truth table definition
● A truth table defines the output of a gate for all possible input
combinations.
● It specifies the inputs (a and b) and the output, based on the gate
type.
● For an and gate, the output will be true only if both a and b are
true.
● For an or gate, the output will be true if either a or b is true.
● For an XOR gate, the output will be true if a and b are different,
and false if they are the same.
● For an XNOR gate, the output will be true if a and b are the same,
and false if they are different.
Logic sim demo
● Logic sim is the simulator used in the class.
● To create an and gate, click on the and gate and set the number of
inputs to two.
● Add two inputs (a and b) and an output (x).
● Connect the inputs to the gate and the output to the output.
● Reset the simulation and adjust the inputs (a and b) to see the
output (x).
● If both inputs are true, the output will be true.
Topic 3. Fundamentals of
Logic Circuit Design
1)Introduction to Logic Design:
Logic Gates
● Logic gates are the basic building blocks that all of logic is built up
from.
● It is important to be familiar with which logic gates are which, their
appearance and how they work.
Truth Tables and Logic Circuits
● Truth tables are a way of writing down what a circuit does.
● Logic circuits are a way of visualizing how to connect up the gates
to do the truth table.
,Karnaugh Maps
● Karnaugh maps are a way to convert truth tables into efficient logic
circuits.
● Computers are better than humans at this task, so not much time
will be spent on it.
Important Logic Blocks
● This is the level of complexity that should be focused on for logic
design.
● When talking about how the processor is built, these kinds of logic
blocks will be used.
Memory Arrays
● Logic blocks can be put together to build a memory array.
Counter
● A counter needs to keep track of the current count, which is its
state, and also needs a clock to determine how fast it counts.
● This is the same clock that determines how fast a processor runs.
, 2)Basic Logic Gates:
What are logic gates?
● Logic gates are the smallest unit of logic circuits used to build up
logic.
● They are the basic stuff used when constructing logic circuits.
● The standard basic gates are the not gate (inverts the input), and
gate (true if both inputs are true), or gate (true if either input is
true), NAND gate (not a and b), XOR gate (true if inputs are
different), and XNOR gate (true if inputs are the same).
Truth table definition
● A truth table defines the output of a gate for all possible input
combinations.
● It specifies the inputs (a and b) and the output, based on the gate
type.
● For an and gate, the output will be true only if both a and b are
true.
● For an or gate, the output will be true if either a or b is true.
● For an XOR gate, the output will be true if a and b are different,
and false if they are the same.
● For an XNOR gate, the output will be true if a and b are the same,
and false if they are different.
Logic sim demo
● Logic sim is the simulator used in the class.
● To create an and gate, click on the and gate and set the number of
inputs to two.
● Add two inputs (a and b) and an output (x).
● Connect the inputs to the gate and the output to the output.
● Reset the simulation and adjust the inputs (a and b) to see the
output (x).
● If both inputs are true, the output will be true.
