Truth Tables | Computer for GCSE/IGCSE - Year 11 PDF Download

NOT gate

• A NOT gate has one input and produces an opposite output by inverting it.
• A is the input
• Z is the output

AND gate

• An AND gate requires two inputs to produce an output.

• The AND gate's truth table demonstrates that only when both inputs are 1, a positive output is produced.

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OR Gate

• An OR gate requires two inputs to operate.

• The truth table illustrates that an OR gate generates a 1 output if any of its inputs are 1.

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NOR Gate

• A NOR gate also has two inputs.

• The truth table demonstrates that a NOR gate functions in the opposite manner to an OR gate; the only input combination that yields a 1 output is when both inputs are 0.

NAND Gate

• A NAND gate has two inputs 

• The truth table indicates that a NAND gate operates inversely to an AND gate; the only input combination that does not produce a 1 output is when both inputs are positive (1 +1).

The XOR Gate

• The XOR gate has two inputs.

• The truth table illustrates the functioning of an XOR gate: it only produces a 1 output when the two inputs are not identical.
• When constructing a truth table for multiple inputs, start by listing the potential input combinations in the leftmost columns.

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A truth table for a three input (A, B and C) logic gate

• The rightmost column displays the ultimate output of the logic circuit (Z).
• Intermediate columns situated between the inputs and the final output aid in determining the ultimate output by holding intermediary results.
• These intermediary results represent the outputs of gates present within the logic circuit.
• Within the given logic circuit diagram, D and E serve as intermediary outputs.

• The fourth column labelled D represents the output of NOT A
  
• The subsequent intermediary output, E, is determined by the logic expression ((NOT A) AND B). This notation is known as a logic expression. 
• The E intermediary output is calculated by executing the AND logical operation on columns B and D.
  
• The final output (Z) can be worked out by performing the OR logical operation on columns E and C