Circuit

• A bunch of logic gates combined
  • Output of one gate --> input of another
  • Flow of electricity is controlled by the interacting gates
• Equivalent when they produce the same output for identical input

Combinational Circuits

• Circuit whose output is solely determined by its input values

Sequential Circuits

• Circuit whose output is a function of its input values and the current state of the circuit

Adders

• Performs addition operation on binary values

Half Adder

• Computes the sum of two bits and produces the appropriate carry bit
• An XOR and an AND gate
• Doesn't allow a possible carry coming in the calculation

Full Adder

• Computes the sum of two bits, taking an input carry bit into account

Multiplexers

• Input control signals determine which input is routed to its output
  • Many input lines
• Often called a mux
• Values on $n$ input control lines determine which of $2^n$ other data lines are selected for output
• Demultiplexer (demux) is the opposite of a mux
  • Single input --> one of $2^n$ outputs depending on values of $n$ control lines

Circuits as Memory

• Can store information
• Sequential circuit
  • Output serves as input
  • Existing state of circuit is used to determine next state

S-R Latch

• Stores single bit
• Guarantees two outputs ($X$ and $Y$) are always complements of each other

Integrated Circuits

• A chip
• Piece of silicon on which multiple logic gates have been embedded
• Classified by the number of logic gates contained in them

Electricity Computer Science