Hi Mentees! I welcome you on behalf of The Engineering Projects. In this section of this DLD Logic gates series, we are discussing different applications of logic gates. We have discussed DLD Adders and Subtractors in our previous lectures and now it's time to have a look at DLD Multiplexers.
When I heard the word Multiplexer, I thought that as Adder adds numbers, Subtractor subtracts numbers, similarly, the Multiplexer will multiply binary numbers but that's not the case. Multiplexer is defined as:
A Multiplexer is also called Data Selector, Universal Logic Selector, Many-to-one Logic converter and Parallel-to-Serial Convertor because it has the ability to select a single input from multiple inputs.
Let's understand the working principle of Multiplexer in detail:
Let's take the example of the simplest multiplexer i.e. 2-to-1 MUX. It has 2 normal inputs(A1 , A2 ) and 1 Select Input(S) and it generates single Output(Y). Here's the block diagram of a simple 2-to-1 Multiplexer:
As discussed above, the selection of inputs is controlled by the Select Pin(S). So, if S = 0, the output will be A1 and if S = 1, the output will be A2. The relation between Select Input and Output is shown in the below truth table:
Select Input(S) | Output(Y) |
0 | A1 |
1 | A2 |
We can understand from the above truth table that we can control maximum 2 inputs from a single Select Input. So, in order to control more than 2 inputs, we need to increase the number of Select Inputs. For example, 2 Select Inputs can control a maximum of 4 Normal Inputs. So, the relation between Select and Normal Inputs can be described by the following formula:
Normal Inputs = 2n
where, n represents the Select Inputs.
So, if we have 5 Select Inputs, we can easily control 25 = 32 Normal Inputs.
Considering the expression above we get the Truth Table of 2-to-1 Multiplexer as follow:Y=D0S' + D1S
S | D0 | D1 | Y |
0 | 0 | 0 | 0 |
0 | 0 | 1 | 0 |
0 | 1 | 0 | 1 |
0 | 1 | 1 | 0 |
1 | 0 | 0 | 0 |
1 | 0 | 1 | 1 |
1 | 1 | 0 | 1 |
1 | 1 | 1 | 1 |
"An OR Gate is a two input Logical Gate that give the output LOW only when both the outputs are LOW."
S | D0 | D1 | Y |
0 | 0 | 0 | 0 |
0 | 0 | 1 | 1 |
1 | 0 | 0 | 1 |
1 | 0 | 1 | 1 |
" The AND Gate is the one that consist of two inputs and gives the input HIGH only when both the Inputs are HIGH."Follow the simple steps to use 2-to 1 MUX as an AND Gate.
S | D0 | D1 | Y |
0 | 0 | 0 | 0 |
0 | 1 | 0 | 0 |
1 | 0 | 0 | 0 |
1 | 1 | 0 | 1 |
"The NOT Gate is a 1 input invertor Logic Gate that gives the output 1 when input is zero and vice versa."To use the 2 to 1 MUX as NOT Gate, just follow the steps:
You can check our website for the XNOR, XOR and NOR Gate from 2 to 1 MUX in our Tutorials. Consequently, today we leaned interesting Circuits. We saw what are 2 to 1 Multiplexers. We made a circuit of the 2 to 1 MUX and from the circuit, we found how can we use them as OR, AND and NOT logic Gates along with the truth tables of each.
- Set the D0 input as 0.
- Set D1 as 1.
- Change the value of S as 1 and zero one after the other.
- You will Observe that when S=1 the output is 0 and vice versa.
- Hence this is our required result.
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