let's do a comparison between the combinational and sequential circuits so I am just doing this lecture before I start the combinational circuit and once we are completed with our combinational circuit we will move to these sequential circuits so I think it is a better way to start a combinational circuit by comparing it with the sequential circuit so let's move to our combinational circuit a combinational circuit is one in which the output the output is only dependent on the present input so let me write it down the output is only dependent on present input ok present input now the sequential circuit is just opposite to it the output depends upon the present input but also it depends upon the previous output or outputs so the sequential circuit is something in which the output depends on deed president input as well as previous output or how birds okay so this is the basic difference between the combination and sequential circuit but there are some more important things that we have to see in that so let's move to one of the example in the combinational circuit and it is the adder the error is a combinational circuit and after this lecture we will start our half adder and full adders so in adder it is very simple let's say if you are adding a single bit if you are adding one with zero then what you are going to get you are going to get one okay so is there any use of the previous output in this adder definitely not there is no need of the previous output in this particular Edition so it is satisfying our condition that the output is only dependent on the present input but if I are if I say about a counter a counter is a sequential circuit that we will complete at the end of this lecture series so in counter what actually happens in your stopwatch or in your devices like which counts the time what happens it just add 1 or increment 1 to the previous output it it increment 1 to the previous output for example if it is counting 5 then it means that the previous output was 4 it added 1 to it to make it 5 similarly if the previous input was 3 it added 1 to get 4 so for its operation it required the information of the previous output whereas in the combinational circuit we do not require any information about the previous of output okay so how this information the previous output is stored in the sequential circuit it is done by a memory element that we call as the flip-flops which is a very important thing in in this digital electronic course so if I make a combinational circuit like this and I say that there are three inputs to this combinational circuit and three outputs to it then it will be very simple the outputs these are our outputs and these are our inputs and this is our combinational circuit fine the output is only dependent upon this inputs but if I want to make a sequential circuit then what I have to do I have to first make a combinational circuit this is our combinational circuit in which there are three outputs same as in this case let us say three inputs okay this is our combinational circuit now to make it a sequential circuit we need we need a memory element this one is our memory element because we need to store the previous outputs and it is stored in this memory which is flip-flop actually so it goes the output goes into the memory element and from memory element it goes back as one of the inputs okay so depending upon this input and this inputs from the memory element the output is generated and again the output is stored in this memory element so there is a positive positive feedback this is the feedback okay this thing going from the memory element to the your sequential circuits is the feedback so there is a positive feedback in the sequential circuit which is very important thing and also there is a memory element involved so only difference between a combinational circuit and a sequential circuit is that there is a feedback involved which is positive and also a memory element to store the previous outputs and the next output is generated depending upon the feedback from the memory element and the present inputs so what we say let me revise it a gained the output is only dependent on the present input whereas in sequential circuit it depends upon the present input as well as the output from the previous inputs so this is all I think in the combinational and sequential circuits comparison and after this we will study our half adder which is one of the combinational circuit we will complete combinational circuit first then we will move to the sequential one so see you in the next presentation