Logic Circuits (Cambridge International IGCSE Computer Science)

Spec point — 6.3.2 · "3 (a) Use logic gates to create given logic circuits from a: (i) problem statement (ii) logic expression (iii) truth table"

Logic Circuits

What is a logic circuit?

• A logic circuit performs logical operations on binary information
• Logic gates are core components of logic circuits
• Based on the arrangement of logic gates and the input signals, the circuit performs a specific function
• A logic diagram is a visual representation of a combinations of logic gates within a logic circuit
• Brackets are used to clarify the order of operations
• An example logic diagram for the Boolean expression Q = NOT(A OR B) would be:

• In the logic diagram above, the inputs are represented by A and B
• P is the output of the OR gate on the left and becomes the input of the NOT gate
• Q is the final output of the logic circuit

Exam Hint You may be asked to draw a logic circuit from a logic statement or a Boolean expression OR write the logical expression that is expressed in the logic diagram using Boolean expression operators

Logic circuits will be limited to a maximum of three inputs and one output

Example of combining logic gates

• P = (A OR B) AND NOT C

Worked Example A sprinkler system switches on if it is not daytime (input A) and the temperature is greater than 40 (input B)

Draw a logic circuit to represent the problem statement above

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