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Sequential Circuits By : Ali Mustafa

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By : Ali Mustafa Sequential Logic Example Sequential Circuit Sequential Circuit Sequential Circuit Storage elements

• What’s required from storage element?

–Store data (hold)–Accept writing a new data (write) Types of storage (memory) elements

Memory Elements Clock Signal• Each sequential circuit has timing signal.

• Clock is a rectangular signal– Duty cycle of 50 %

• Clock signal repeat itself after T seconds

• So the clock frequency is F = 1 / T

1 Clock Time Clock Delay(Skew)

• Defined as a difference in time between the clock edges arriving at a pair of clock input.

• In real time ,the edges do not arrive at exactly the same time & there is some skew.

• The MAX allowable skew for the system is the difference between the longest & the smallest skew.

• The major reason for skew are– Different length of wires used

– Multiples gate levels What’s the Clock Basic memory element• Basic memory element consists of two inverters

cascaded and the output of the last inverter is fed back to the input of the first inverter.

• Q and Q‟ are the outputs of the memory element.

– Set State Q=1 , Q’=0

– Reset State Q=0 , Q’=1

– Invalid State Q=Q’

• This memory element will always store one bit. Sequential Logic : Asynchronous Sequential Logic : Asynchronous Sequential Logic : Synchronous Sequential Logic : Synchronous Sequential Logic : Synchronous Sequential Logic : Memory Element SR Latch SR Latch S’R’ Latch : NAND gate latch Sequential Logic : Flip Flop Sequential Logic : Flip Flop Sequential Logic : Flip Flop Sequential Logic : Flip Flop Sequential Logic : Flip Flop Sequential Logic : Flip Flop Sequential Logic : Flip Flop Sequential Logic : Flip Flop Sequential Logic : Flip Flop Sequential Logic : Flip Flop Sequential Logic : Flip Flop Sequential Logic : Flip Flop Sequential Logic : Flip Flop Sequential Logic : Flip Flop Sequential Logic : Flip Flop Sequential Logic : Flip Flop D Flip Flop D Flip Flop D Flip Flop D Flip Flop D Flip Flop JK Flip Flop JK Flip Flop JK Flip Flop T Flip Flop Master slave using SR Latch Master-Slave using D Flip-Flop Comparing Flip Flop and Latch Standard Symbols for Storage Elements