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

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 `D`

.
The JK flip-flop has output _{X}`Y`

. Its inputs also have no names so let's call them
`J`

, and _{Y}`K`

.
We can then give formulas for the combinational logic inputs of each flip-flop input as follows:
_{Y}

`D`

_{X}= A nand B`J`

_{Y}= X or Y`K`

_{Y}= A nand B

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

Copyright © 2014 Barry Watson. All rights reserved.