Flip-Flop Input Equation

The combinational logic circuit inputs to a flip-flop are described by a flip-flop input Boolean equation.

Example

Consider the following sequential logic circuit containing a JK flip-flop and a D flip-flop (not all connections are shown to keep the schematic simple):

The D flip-flop has output X. Its input has no name, so let's call its input DX. The JK flip-flop has output Y. Its inputs also have no names so let's call them JY, and KY. We can then give formulas for the combinational logic inputs of each flip-flop input as follows:

• DX = A nand B
• JY = X or Y
• KY = A nand B

References

Mano, M. Morris, and Kime, Charles R. Logic and Computer Design Fundamentals. 2nd Edition. Prentice Hall, 2000.