1. The problem statement, all variables and given/known data I'm working on this problem but everytime I tried to walk through my answer it doesn't seem right. I wanted to built a ripple counter, up counter with mod 13 using D flip flop. 2. Relevant equations present state ABCD - 0000-->1101 next state ABCD - 0001-->0000 Q(t+1) = Dq 3. The attempt at a solution I first built the state diagram going from 0000 to 1101 then back to 0000. Now the text book said to use take the compliments of the output from the D flip flop. So what I did I took the compliment of the output(next state) and the unused state (14 and 15 as don't care) and by k-map i constructed a formula for the 4 D-FF. However as soon as I hit 13(1101) it will not go back to 0000. The other approach is: I took the output from the next state and the unsued state(1110 and 1111 as don't care states), using k-map again i constructed a formula for the sum of product of the 4 D-FF. But agian it will not go from 1101 to 0000. Then I redo it by using complements output of the next state with k-map to built the formula for the FFs without the unused state and it still doesn't work. I redo it agian by using output of the next state with k-map to built the formula for the FFs without the unused state and still doesn't work. I know that I'm doing something wrong during the process, however I'm not sure howelse to built this FFs.