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Unformatted text preview: 10/8/09 1 1 ECE2030 Introduction to Computer Engineering Lecture 14: Sequential Logic Circuits 2 Sequential Logic Circuits Sequential circuits Combinational logic circuits State information (stored in memory) using Latches/Flip-Flops Output is a function of inputs and present state Combinational circuits inputs outputs Storage Element Control er by a periodic clock or an event trigger 3 Types of Sequential Circuits Synchronous Behavior defined from knowledge of signals at discrete instances of time Storage elements observe inputs and can change state only in relation to a timing signal (clock pulses from a clock ) Asynchronous Behavior defined from knowledge of inputs at any instant of time and the order in continuous time in which inputs change If clock just regarded as another input, all circuits are asynchronous! Depends on the time s at which: storage elements observe their inputs, and storage elements change their state 4 Time Behavior Example: A 2-Input NAND gate with a 0.5 ns. delay: Assume A and B have been 1 for a long time At time t=0, A changes to a 0 at t= 0.8 ns, back to 1. F A B DELAY 0.5 ns . F(Instantaneous) t (ns) A B F(I) F Comment 1 1 A=B=1 for a long time 1 1 1 F(I) changes to 1 0.5 1 1 1 F changes to 1 after a 0.5 ns delay 0.8 1 1 1 1 F(Instantaneous) changes to 0 0.13 1 1 1 F changes to 0 after a 0.5 ns delay 10/8/09...
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This note was uploaded on 11/24/2009 for the course ENGINEERIN 4283 taught by Professor Smith during the Spring '09 term at American InterContinental University Dunwoody.
- Spring '09