A PN flip$-$flop has four operations: set to $1$complement, no change, and clear to $0$ when inputs P and N are $00,01,10,$ and $11,.$

The excitation table is

Oa$.0$ X$1$X$,$ X $0$ and X $1$ when Q$($t$)$ and Q$($t$+1)$ are $00,01,10,$ and $11,$ respectively.

bx $0$x $10$ X and $1$ X when Q$($t$)$ and Q$($t$+1)$ are $00,01,10$and $11$respectively.

C$.1$X$,0$ XX $1$ and X $0$ when Q$($t$)$ and Q$($t$+1)$ are $00,01,10,$ and $11,$ respectively.