 Today we will discuss about multiplexer and demultiplexer. At the end of this session student will be able to design multiplexers and demultiplexers using gates. What is multiplexer? A multiplexer is digital switch that has multiple inputs or sources and single destination that is output. Here the select line determines which input is to be connected to the output. We can see in the block diagram four inputs are there, one input, one output and one select line is there. We will take idea about what is the multiplexer with general example. If we want to watch one new channel we are having many options in our TV like NDTV, CNN, Starnews, IBM, ABP. And if I want to choose one of that that is Starnews then I require remote to choose that. So here remote is working as a switch to select that Starnews. So same that remote work will be work into the multiplexer. Multiplexer are many types 2 to 1, 4 to 1, 8 to 1 and 16 to 1 as per our requirement. So this is the first circuit diagram of 4 to 1 multiplexer or MUX. We are having D0, D1, D2 and D3 inputs and Y output. Now when we want to select one of this we need two select lines as four options are there. So A and B both are select lines. So the combination of A and B we will see one by one, 0 and 0 it will select D0 line. When B is 0 and A is 1 it will select D1 line. When B is 1 and A is 0 the input D2 will be selected for output display and B is 1 and A is 1 will be selected for D3 input as output. So we will see how the multiplexer waveforms are there for 4 to 1. As we have already seen that there are four inputs D0, D1, D2 and D3 and select line here again we are showing with A and B waveform, D0, D1, D2, D3 whatever the data is there it will not be considered only A and B waveforms will be considered for selection of the input. So when A is 0 and B is 0 at that time D0 is selected in this diagram we are showing that as a red line. Then A is high and B is low that time D1 is going to be selected D1 is showing with red line and third option as in the waveform we have seen that A is low B is high at that time D2 is selected and that both are high A and B high that time D3 is get selected. So same we are having 1 to 8 D multiplexer where we can see D0, D1, D2, D3, D4, D5, D6 and D7, 7 inputs are there now here 7 combinations of inputs are there. So we need 3 select line so that we can reproduce that input for 1 output. So here we are using AND gates and 1 OR gate is there AND gate is helping all the select line and 1 input line. So for example when D0 we want to select D0 is D0, D1 all data lines will be high always so D0 will be high and then we can see that A, B, C whatever the select lines are there 3 lines are there they are going through the NOT gate so all will be 1 at 0 0 0 combination. So that AND gate will reproduce that output 1 so D0 is going to be selected for output. Now D multiplexer it is exactly opposite to the multiplexer in multiplexer we have seen there are many input and one output but in D multiplexer we are having one input and many output many output means one of the output is going to be selected to transfer that data. So what is D multiplexer? A D multiplexer is a digital switch with a single input that is source and a multiple output that is the destination and again we are having select line to determine which output is getting selected for displaying the output. Now here again the block diagram we can see that one input is there and 4 outputs are there and one select line is there. In D multiplexer again we are having different types 1 to 2, 1 to 4, 1 to 8 and 1 to 16. So for example we are just checking here 1 to 4 D multiplexer here input is X that is the single input for this and outputs are D0, D1, D2, D3. Before going to this multiplexer circuit diagram I will show one example for this which we are using in daily basis that is whatever our PC is there whatever the data is on our PC. Then we are transferring that data to either printer or fax machine or color printer or paint plotter. So when I want to use one of this now for example fax machine then the PC data will be connected to the fax machine with the help of Demux. Now when I want to select fax machine you can see that B should be 0, A should be 1 that is the select lines and then it will be selected fax line and the data on the PC will be transferred to the fax line. So this is the example of the Demux. Now here we will again see 1 to 4 D multiplexer circuit diagram. X is input D0, D1, D2, D3 are output and the truth table is given over there. Now when 00 both select lines are there that time only D0 is getting selected as they are inverting A and B and giving to the AND gate. So AND gate is getting 1, 1 and input is 1. So it will be given to the D0. Then 0 when B is 0 A is 1 that time D1 is going to be selected, B is 1 A is 0 that time D2 is selected and when both inputs are 1, 1 D3 is going to be selected. So here we will see the waveforms X is input and here S0 and S1 are select lines. So as we have seen in this example S0 and S1 when both are low, D0 is getting selected and when S0 is 1, S1 is low that time D1 is selected. When both are high that time D3 is selected and S0 is low, S1 is high that time D2 is getting to be selected. So one question that is can you find more example for the multiplexer? So answer there are many answers but I have choose two answers here that is any communication channel like radio in the radio you are having many channels and you can select one of the channel using this multiplexer circuit or in the telephone system when you want to select one of the number in the telephone system then you have to use the switching system that is multiplexer. The references for this thank you.