L10-sequential-2009

# L10-sequential-2009 - Sequential Logic Circuits Trac D....

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1 Sequential Logic Circuits Sequential Logic Circuits Trac D. Tran ECE Department The Johns Hopkins University Baltimore, MD 21218 Outline Outline ± Sequential logic and memory elements ² Set-Reset flip-flop ² Toggle flip-flop or edge-triggered flip-flop ² Sequential circuits as finite state machine ± Applications ² Car Alarm ² Modulo-N binary counter ² Random access memory (RAM)

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2 Sequential Logic Sequential Logic ± Combinatorial logic circuits: current input values determine the output value ± Sequential logic circuits: output value also depends on past input values. Sequential logic circuits have memory ± Common memory elements ² Set-Reset Flip-Flop (SR-FF, RS Latch): basic computer memory cell ² Toggle Flip-Flop (T-FF): basic computer counting cell Set Set -Reset Flip Reset Flip -Flop Flop Q Q S R 1 1 1 1 0 1 0 1 1 0 1 0 Q Q 0 0 Q Q R S Comment hold reset set strange state Timing Diagram S R Q Q
3 SR SR -FF Analysis FF Analysis Q Q S R S R Q Q 0 1 1 0 0 1 0 1 0 1 0 0 Q Q S 0 1 1 0 0 1 0 1 0 1 0 0 Q R Q initial state set transition reset transition ± Q remembers which input, S or R, was 1 last ± If S then Q=1 ± If R then Q=0 Set Set -Reset Flip Reset Flip -Flop: On Hold Flop: On Hold Timing Diagram S R Q Q Q Q S R ± Initial state:

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## This note was uploaded on 02/02/2010 for the course ENGINEERIN 520.101 taught by Professor Tracdtran during the Winter '06 term at Johns Hopkins.

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L10-sequential-2009 - Sequential Logic Circuits Trac D....

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