Levels of Abstraction
Transistors
CS 21 - Computer Organization and Assembly Language Programming Lecture 9 Levels of Abstraction: Transistors to Gates University of the Philippines - Diliman College of Engineering Department of Computer Science
Gates
Levels of Abstraction
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Levels of Abstraction
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Levels of Abstraction
hierarchical view of systems where details are made abstract, level by level used by people to avoid being overwhelmed by details the higher the level is, the less detail you see highest level is the system itself
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Levels of Abstraction
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Transistors
What are transistors? building blocks of modern electronic devices has three terminals: drain/sink, gate, source control device: input in one terminal controls flow of current in the other two made of semiconductors, usually silicon(why?)
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Levels of Abstraction
Transistors
Schematic symbol and parts
gate is input current which flows from source to sink is output
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Levels of Abstraction
Discrete component
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Layout
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Microscopic View
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Response Curve
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Levels of Abstraction
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Analogy: Tap
turning the tap induces water to flow applying current to gate causes current to flow what does this say about about the input and output of transistors? are they continuous or discrete?
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Levels of Abstraction
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Analogy: Light Switch
has only two states: on or off very convenient in modeling the transistor as a binary device
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Levels of Abstraction
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A switch in action
What would happen if we press the switch?
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Truth table Assuming that the the switch being pressed is ”1” and the light being turned on is ”1”, what is the truth table for the following diagram?
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Switches in action Our simple light bulb circuit could also feature multiple switches/inputs:
What is the truth table for this one?
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Levels of Abstraction
Switches in action
How about this one?
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From transistors to gates
What are logic gates? components that implement logic functions physically composed of interconnected switches
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Levels of Abstraction
From this...
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To this
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Gates
there are only a limited number of gate types, which could then be interconnected to perform more complicated logic functions the output of another gate could become the input of another with the exception of the INVERTER, all gates have 2 inputs or more
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Levels of Abstraction
NOT
inverts value of input operation symbol is overbar
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AND
to get output of ”1”, ALL inputs must be ”1” operation symbol is ”.” output could be negated to form operation NAND
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OR
to get output of ”1”, at least ONE input must be ”1” operation symbol is ”+” output could be negated to form operation NOR
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XOR
to get output of ”1”, number of inputs with value ”1” must be ODD operation symbol is ”+” with circle
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Basic Logic Operations
Levels of Abstraction
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Network of gates
Assuming A=1, B=1, C=0, and D=0, what would be the output of the following network of gates?
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Levels of Abstraction
Transistors
Network of gates
Assuming A=1, B=1, C=0, and D=0, what would be the output of the following network of gates?
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Levels of Abstraction
Transistors
Network of gates
Assuming A=1, B=1, C=0, and D=0, what would be the output of the following network of gates?
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Levels of Abstraction
Transistors
Network of gates
Assuming A=1, B=1, C=0, and D=0, what would be the output of the following network of gates?
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Levels of Abstraction
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Gate delay
after asserting input, the output does NOT become available immediately the amount of time between the assertion of input and the availability of output is called the gate delay
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