Sequential logic design

Sequential logic design

• A sequential circuit is a digital circuit whose outputs are a function of the current as well as previous input values.
• Sequential logic possesses memory.
• One of the most basic sequential circuits is the flip-flop.
• A flip-flop stores a single bit.

D-Flip-Flop

• The simplest type  of  flip-flop  is  the  D  flip- flop.
• It has two inputs: D and clock.
• When clock is 1, the value of D is stored in the flip-flop output Q.
• When clock is 0, the value of D is ignored; the output Q maintains its value.

SR-Flip-Flop

• An SR flip-flop has threee inputs S,R,clk
• S stands for Set and R stands for Reset.
• When clock is  0,  the  previously  stored  bit  is maintained and appears at output Q.
• When clock is  1,  the  inputs  S  and  R  are examined.
• If S is 1, 1 is stored in Q.
• If R is 1 , 0 is stored in Q.
• If both are 0s there is no change
• If bothe are 1s behavior is undefined.

JK-Flip-Flop

• An JK flip-flop has three inputs J,K,clk
• JK flip-flop is same as  that  of  SR  flip-flop except that when J and K are 1, the stored bit toggles from 1 to 0 or 0 to 1.
• When clock is  1,  the  inputs  J  nad  K  are examined .
• If J is 1, 1 is stored in Q.
• If K is 1 , 0 is stored in Q.

• If both are 0s there is no change
• If bothe are 1s output toggles.

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