L08-TransistorsLogic - Transistors and Logic A 1) 2) 3) 4)...

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L08 – Transistors and Logic 1 Comp 411 – Fall 2009 9/30/09 Transistors and Logic A B Comp 411 Box-o-Tricks F = A xor B 1) The digital contract 2) Encoding bits with voltages 3) Processing bits with transistors 4) Gates 5) Truth-table SOP Realizations 6) Multiplexer Logic
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L08 – Transistors and Logic 2 Comp 411 – Fall 2009 9/30/09 Where Are We? Things we know so far - 1) Computers process information 2) Information is measured in bits 3) Data can be represented as groups of bits 4) Computer instructions are encoded as bits 5) Computer instructions are just data 6) We, humans, don’t want to deal with bits… So we invent ASSEMBLY Language even that is too low-level so we invent COMPILERs, and they are too rigid so … But, what PROCESSES all these bits?
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L08 – Transistors and Logic 3 Comp 411 – Fall 2009 9/30/09 A Substrate for Computation We can build devices for processing and representing bits using almost any physical phenomenon neutrino flux trained elephants engraved stone tablets orbits of planets sequences of amino acids polarization of a photon Wait! Those last ones might have potential. .. 1 0 1 0 0 1 1 0 1 0 0 1
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L08 – Transistors and Logic 4 Comp 411 – Fall 2009 9/30/09 Using Electromagnetic Phenomena Things like: voltages phase currents frequency For today let’s discuss using voltages to encode information. Voltage pros: easy generation, detection voltage changes can be very fast lots of engineering knowledge Voltage cons: easily affected by environment need wires everywhere
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L08 – Transistors and Logic 5 Comp 411 – Fall 2009 9/30/09 Representing Information with Voltage Representation of each point (x, y) on a B&W Picture: 0 volts: BLACK 1 volt: WHITE 0.37 volts: 37% Gray etc. Representation of a picture: Scan points in some prescribed raster order… generate voltage waveform How much information at each point?
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L08 – Transistors and Logic 6 Comp 411 – Fall 2009 9/30/09 Information Processing = Computation First, let’s introduce some processing blocks: (say, using a fancy photocopier/scanner/printer) v Copy v INV v 1-v
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L08 – Transistors and Logic 7 Comp 411 – Fall 2009 9/30/09 Let’s build a system! ? Copy INV Copy INV Copy INV Copy INV output (In Theory) (Reality) input
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L08 – Transistors and Logic 8 Comp 411 – Fall 2009 9/30/09 Why Did Our System Fail? Why doesn’t reality match theory? 1. COPY Operator doesn’t work right 2. INVERSION Operator doesn’t work right 3. Theory is imperfect 4. Reality is imperfect 5. Our system architecture stinks ANSWER: all of the above! Noise and inaccuracy are inevitable; we can’t reliably reproduce infinite information-- we must design our system to tolerate some amount of error if it is to process information reliably .
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L08 – Transistors and Logic 9 Comp 411 – Fall 2009 9/30/09 The Key to System Design A SYSTEM is a structure that is guaranteed to exhibit a specified behavior, assuming all of its components obey their specified behaviors.
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L08-TransistorsLogic - Transistors and Logic A 1) 2) 3) 4)...

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