Assignment : Digital Logic

Assignment : Digital Logic

Definitions Of Digital Logic

• Combinational logic : a digital logic circuit in which logical decisions are made based only on combinations of the inputs. e.g. an adder.
• Sequential logic : a circuit in which decisions are made based on
combinations of the current inputs as well as the past history of
inputs. e.g. a memory unit.
• Finite state machine : a circuit which has an internal state, and
whose outputs are functions of both current inputs and its internal state. e.g. a vending machine controller.

A Truth Table

• Developed in 1854 by George Boole.
• Further developed by Claude Shannon (Bell Labs).
• Outputs are computed for all possible input combinations (how many input combinations are there?)
• Consider a room with two light switches. How must they work?

Logic Gates and Their Symbols

• Logic symbols shown for AND, OR, buffer, and NOT Boolean functions.
• Note the use of the “inversion bubble.”
• (Be careful about the “nose” of the gate when drawing AND vs. OR.)

Variations of Logic Gate Symbols

The above table is a summary truth table of the input/output combinations for the NOT gate together with all possible input/output combinations for the other gate functions. Also note that a truth table with 'n' inputs has 2ⁿ rows. You can compare the outputs of different gates.