CSC 110  Intro. to Computing Lecture 5: Gates, Circuits, & Transistors.

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Transcript of CSC 110  Intro. to Computing Lecture 5: Gates, Circuits, & Transistors.

CSC 110 Intro. to ComputingLecture 5:Gates, Circuits, & Transistors

AnnouncementsHomework available on BlackboardHomework due Friday at 4:00PMHand to me or put in my box in Wehle 207Quiz on this material next ThursdayQuiz last week went fairly wellTop was 100; Mean was 77 ( = 20.7)Scores available on BlackboardCome to my office to pick up your quiz

AnnouncementsCSC tutors are now availableHours posted outside Wehle 208Also come to my office hours, make an appointment, or call/email me questions

Circuit DesignIn your group, complete work with circuitsCompute the truth tables for circuitsDraw the diagrams for these equations

Truth Table
Sheet1
abcc'a+bc'+b(a+b) * (c' + b)
0001010
0010000
0101111
0110111
1001111
1010100
1101111
1110111

Truth Table
Sheet1
abca'(a'+b)(a+c)'(a'+b) * (a+c)'
0001111
0011100
0101111
0111100
1000000
1010000
1100100
1110100

Circuit Design

Circuit Design

Algebraic PropertiesLaw of Double Negation: a = a
Sheet1
PropertyANDOR
Commutativeab = baa + b = b + a
Associative(ab)c = a(bc)(a + b) + c = a + (b + c)
Distributivea(b + c) = ab + aca + (bc) = (a + b)(a + c)
Identitya1 = aa + 0 = a
Complementa(a') = 0a + a' = 1
DeMorgan(ab)' = a' + b'(a + b)' = a'b'
Idempotencyaa = aa + a = a

Improving Circuit Design

Improving Circuit Design

Circuit Propagation DelayTime taken for signal to get through circuitImportant measure when building processorGate cannot generate results until it has all of its inputsEach gate starts at the time of the latest input Each gate requires a set amount of time to completeCould be specific amount of time (e.g., 10 ps)Or state result as multiple of gate delays

How are these improved?How long will this circuit need to complete?

How are these improved?How long will it take for the signal to propagate through?

Circuit Delay PropagationWhat is the propagation delay for this circuit?

Circuit Delay PropagationWhat about this circuit?

TransistorsTransistors used to implement gatesUses a semiconductive materialMaterial can serve as both conductor and insulatorSilicon is the preferred semiconductor because of cost. Why is it so cheap?

TransistorsOriginally invented by Bell Labs in 1947Have been improved since thenCan switch onandoff in nanosecondsEach transistor dissipates energyWhy is this be a problem?

My View of TransistorSource

My View of TransistorGround

My View of TransistorOutput

My View of CircuitInput: Franklin off flying a kite

My View of CircuitInput: Franklin on poking key

Engineers View of a CircuitSource connects system powerAlways at +5V (e.g. high state or 1)Ground drains transistors energyLeaves transistor at +1V (e.g. 0)When Vin controls baseActs like onoff switchWhen on, source drains into groundWhen off, source signal sent to Vout

Transistor DesignTurns out NOT, NAND, and NOR are easiest gates to turn into transistorsHow do these work?

Transistor DesignApple wanted NANDbased memory (rather than NORbased) for iPod Nano. Why?

Combinatorial CircuitsSo far, all circuits have been combinatorialOutput is determined only by input valuesWhy would we need other circuits?

Sequential CircuitsSequential circuits include another featureOutput determine by inputs AND current stateUsed when current state is important detailE.g., Memory

SR LatchSR latch stores single binary digit (1 or 0)Result is value of X
Inputs stand for Set and ResetCould also be implemented with NOR gatesAdapted from Computer Science Illuminated, Dale and Lewis, p. 112

SR LatchNormally, S & R = 1Maintains value of X
S = 1, R = 0 X = 0Called the set stateS = 0, R = 1 X = 1Called the reset state
Latches also called flipflops

For next lectureStart doing the homeworkStart reading Section 5Be ready to discuss:What Individual Computer Component Descriptions MeanSizesDisksSpeed