22_sequential

# 22_sequential - Review of Combinational Circuits 6.3...

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4/21/08 Copyright 2000, Kevin Wayne 1 Introduction to Computer Science Robert Sedgewick and Kevin Wayne Copyright © 2005 http://www.cs.Princeton.EDU/IntroCS 6.3 Sequential Circuits 2 Review of Combinational Circuits Combinational circuits. Basic abstraction = switch. In principle, can build TOY computer with a combinational circuit. – 255 × 16 = 4,080 inputs 2 4080 rows in truth table! – no simple pattern – each circuit element used at most once Bottom line from last lecture. ALU. Sequential circuits. Reuse circuit elements by storing bits in "memory." Machine architecture. Wire components together to make computer. 3 B A Sequential vs. Combinational Circuits Combinational circuits. Output determined solely by inputs. Can draw with no loops. Ex: majority, adder, ALU. Sequential circuits. Output determined by inputs and previous outputs. Ex: memory, program counter, CPU. Ex. Simplest feedback loop. Two relays A and B, both connected to power, each blocked by the other. State determined by whichever switches first. Stable. 4

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22_sequential - Review of Combinational Circuits 6.3...

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