Truth Tables – A Level Electronics WJEC Revision

A truth table is used in logic and mathematics to depict all the possibilities of input and output for a specific logic gate or a logic circuit.
The inputs and outputs are represented as binary values 0 (false) and 1 (true).
Each row of the truth table represents a specific combination of inputs and the resulting output for that combination.

The fundamental logic gates include: AND, OR, NOT, NAND, NOR, XOR, and XNOR; each with a distinct truth table.
The AND gate gives an output of 1 only when all its inputs are 1.
The OR gate gives an output of 1 if at least one of its inputs is 1.
The NOT gate, also known as an inverter, flips the input; if the input is 1, output is 0 and vice versa.
The NAND (NOT AND) gate produces an inverted AND gate output.
The NOR (NOT OR) gate gives an inverted OR gate output.
The XOR (Exclusive OR) gate only produces a 1 output when its inputs are different.
The XNOR (Exclusive NOR) gate only gives a 1 output when its inputs are the same.

Combinational logic circuits are digital circuits that use the basic logic gates to achieve a specific function, such as binary adders or decoders.
A complex logic problem can be broken down and solved using a combinational logic circuit.
The behavior of a combinational logic circuit can be fully expressed using a truth table, mapping all possible inputs to their corresponding outputs.

De Morgan’s Law is a principle in Boolean algebra that simplifies complex logic expressions and reduces the number of logic gates in a circuit.
The two specific laws are: the complement of the sum of two variables is equal to the product of their complements, and the complement of the product of two variables is equal to the sum of their complements.
De Morgan’s Law can be easily verified using truth tables.