Welcome to this new section.
I'm here and in our previous lectures we have explored the computer's most basic building block, which
was the logic gates.
Now we are ready to move on one step forward, which is logic circuits.
So computers are not built from an individual gates alone, as you have seen so far.
They are constructed from carefully organized groups of logic gates called logic circuits.
Which makes up essential part of computer which works together to process digital information.
And in this and the next lectures, we will dive into how to build some of the fundamental logic circuits
that make up essential parts of a computer like CPU, memory units and other devices.
However, we will not attempt to describe these complex systems in full.
Instead, we will carefully examine a few small but crucial parts of.
Logic circuits and focus on understanding the concepts behind them.
And our main objective is to provide you with a clear and approachable introduction to the principles
that underlie these important circuits.
Logic circuits can be broadly classified into two types the combinational.
And the sequential.
Now let's focus on understanding the difference here.
A combinational logic circuit is one where the output depends only the current inputs at that specific
moment, so there's no memory or dependency on what happened before.
So this system forgets any previous inputs.
In contrast the sequential logic circuit is different.
Here the output depends both on the current input and the past inputs.
And this means the circuit has some form of memory to remember previous states.
Now let's use a similar or familiar example your TV remote control.
Now suppose you enter a number directly like five.
The television immediately switches to channel five.
The output, which is the selected channel, depends only on your current input, which is the number
you typed.
And it does not matter which channel you are watching before you're watching.
You may maybe watching the, uh, 10th.
Channel 15th.
Channel 500th channel on your television.
No matter where.
What are you watching?
If you press the five button, the channel will switch to fifth channel.
Right.
But the sequential logic circuits does not work like that when you press the channel up or channel down
button.
The television needs to know the current channel to decide the next one.
So if we are on the channel fifth, if you press the channel down button, the television needs to know
which channel we are in and add one.
So it will move us to sixth channel.
And if we press the channel up button, the television again needs to know which channel we are in.
So it will, uh, add one on our current channel and switch to channel six.
But yeah.
Or five.
Yeah, it doesn't matter.
You get the logic here.
Now in this, uh, section we will work with the combinational logic circuits in next lectures however.
We will explore sequential logic circuits in depth.
Now, before we get into designing logic circuits, it is very important to understand how digital zeros
and ones are physically represented in electronic circuits.
Now, digital circuits use two different voltage levels to represent the two binary states, as you
have learned so far in this previous lectures.
So a high voltage represents state one and the low voltage represents another state, which is in this
case state law.
So usually uh the higher voltage represents a Presents binary one and the lower voltage represents binary
zero.
But sometimes it can be the other way around, depending on the circuit design.
But in the 99%, 99.99% of the time you will see this same.
So upper voltage represents one.
The zero or lower voltage represents basically zero.
So terminology you must know is in an active high signal.
The one is represented by a high voltage and the zero is represented by the low voltage.
But the actor in an active low signal which is very rare, one is represented by a low voltage and the
zero is represented by the high voltage.
So this one is very rare.
So I'm just explaining it.
So you know that it is not an obligation to use one as a higher volt.
Right.
Or zero as a volt.
So.
An active high input can be connected to active low input.
But the designer must make sure to adapt the signal correctly.
So imagine a device expects a logical one to be a low voltage in this case active volt.
But your signal is active high where one is high voltage.
In this case, you need to invert.
Which also also you can call that complement the signal before connecting these each other to it.
Now this is important in real world electronics because misunderstanding active high low connections
can cause logic errors in circuits.
And the key point for this course is for simplicity.
In this course we will always discuss only in terms of logic levels, zeros and ones without mentioning
their actual values.
But in real design work or data sheets you will often encounter this voltage level terms.
Knowing them helps you communicate professionally with hardware engineers and read technical documents.
Now here we will draw a quick diagrams.
Um, you can on your draw, on your notepad, on your board during this lecture to practice on your
own.
And you may ask here how we can defer defer this combinational logic circuits in a real circuit design
is basically combinational logic circuits gets the outputs.
Gets the inputs, which is basically in n vars and which is variables.
And gives us the basically outputs.
So this is what this is basically a combinational logic circuit.
But here we will have one.
It will have the sequential logic circuit where it will have an input.
Yes it will also have an output but it will also have the memory elements.
So how the memory elements work is you will basically here just will get here.
And yeah that is memory elements.
And here this is basically.
The combinational logic circuit.
But since it has.
So as I said the main difference is here between the combinational and sequential.
The combinational logic circuits is also a logic circuit.
But it it is it also has the memory elements which will practice in this lecture.
So the summary of this lectures is computers are built from logic circuits.
Logic circuits are two types the combinational and sequential Which combination means current inputs
only and the sequential is current plus past inputs plus past inputs.
And in this section we will focus on combinational circuits.
And also you learned that binary ones and zeros are physically represented using different voltage levels.
And it is crucial to understand active high and active low signaling.
And in the next lecture we'll start designing and analyzing basic combinational logic circuits such
as adders multiplexers, decoders.
So prepare your notes and ready to sketch diagrams.
Because visual thinking is a powerful tool when working with low level digital systems.
Now, thank you for watching.
I'm typhoon.
And I'm waiting you in next lecture.