Logic Circuits (Cambridge (CIE) O Level Computer Science)
Revision Note
Written by: James Woodhouse
Reviewed by: Lucy Kirkham
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
Examiner Tips and Tricks
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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