Lecture 4 Flashcards
Circuit
A network that processes discrete-values variables
Can be viewed as a black box
Black box representation
> 1 discrete-valued input terminals
>1 discrete-valued output terminals
Functional specification
Describes relationship between inputs and outputs
Timing specification
Describes delay between inputs changing and outputs responding
Inside the black box, circuits are composed of
Nodes and elements
Element
Itself a circuit with inputs, outputs, and a specification
Node
A wire, whose voltage conveys a discrete-valued variable
Classified as input, output, or internal
Inputs
Receive values from the external world
Outputs
Deliver values to the external world
Internal nodes
Wires that are not inputs or outputs
Combinational circuit’s outputs
Depend only on the current values of the inputs
Combines the current input values to compute the output
Logic gate
Memoryless
Sequential circuit’s outputs
Depend on both current and previous values of the inputs
Depends on the input sequence
Has memory
Functional specification of a combinational circuit
Expresses the output values in terms of the current input values
Timing specification of a combinational circuit
Consists of lower and upper bounds on the delay from input to output
Design constraints
Area, speed power, and design time
Best way to build an OR gate using CMOS transistors
To use a NOR followed by a NOT
Full adder
Combinational circuit with multiple outputs
Bus
Bundle of multiple signals
Combinational composition rules
Every circuit element is itself combinational
Every node of the circuit is either designated as an input to the circuit or connects to exactly 1 output terminal of a circuit element
Circuit contains no cyclic paths: every path through the circuit visits each node at most once
Complement of a variable
It’s inverse
Literal
The variable or its complement
True form of the variable
A
Complementary form of the variable
It’s inverse
Product or an implication
The AND of >= 1 literals