in the last presentation we saw what is deep flip flop and how to get a d flip flop using the SR flip flop that I made here I have complemented the inputs the reason for this I explained in the last presentation that you can follow at the end of that presentation we deduce the truth table for the D flip flop that I made here you're having your clock whenever the clock is low whatever be the value of D your output is not going to be affected it will have the previous value stored in it similarly
when your clock is high D is low D output will be low clock is high D is high the output will be high a very simple truth table to follow Now by using this truth table we are going to have our characteristic table like we did in the SR flip flop you already know in characteristic table we have our output as the next state so let's make this characteristic table the next state will depend on the input as well as the pre previous state so our previous state is qn and the input is D and
my output is qn + 1 next state two inputs four possible combinations so let us first write down the combinations 0 0 1 1 0 1 0 1 okay now let's try to find out the value for Q and + 1 by using this truth table when D is zero it means your qn + 1 is zero so it is simply zero when D is 1 it means qn + 1 is 1 so it's simply one again when D is 0o it's zero and when D is 1 it's one so one thing that you can
see from this characteristic table is that your q n + 1 next state is going to be same as your D the data input so that's what we have evaluated from our character itic table now it's time to move to our excitation table in excitation table the two inputs are qn and qn + 1 okay and the output is D Now by this characteristic table you can directly write the value for D but I'm not going to do that I will tell you at the end that how you could have written the values directly but
we will try to find out so 0 0 1 1 1 0 1 0 1 when qn and qn + 1 both are zero it means this case your D is zero and uh when qn is z q + 1 is 1 which means let me change the color which means this case your D is one and when your qn is 1 Q + 1 is 0 which means this case again your D is zero and till now you have seen that D is equal to qn + 1 that I have already evaluated and for
the last case also your D is equal to qn + 1 so 1 so this is all that you need to know about the characteristic table and the exitation table for the D flip flop it's better to remember that qn + 1 is same as D and uh I'm telling you this thing because when you do the flip-flop conversions and the designing of your counters you're going to require this knowledge very frequently every time you cannot make your characteristic table and excitation table by using the truth table you don't have that much time if they
ask in question you have to convert JK flipflop to D flip flop then you must know these values in the next presentation we are going to do a very important topic that is your JK flipflop in this JK flipflop we will discuss the Master Slave operation as well as the race around condition a very important question for your exam as well as your interviews so see you in the next presentation
