2.4.2

Boolean Logic

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Evaluating Expressions

Logic gates can be combined to form logic circuits that process complex logical statements such as A AND (B OR C).

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Evaluating boolean expressions

  • To evaluate a boolean expression, you should substitute all of the values in for the variables and then use the definitions of the different boolean functions to simplify it one step at a time.
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Order of evaluation

  • You should evaluate any expression in brackets first, for example:
    • NOT(True OR False).
    • NOT(True).
    • False.
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Truth tables

  • Another method of evaluating an expression is using a truth table.
  • A truth table shows every possible combination of inputs and the resulting output.
  • The truth table shows the input and output state for each combination.
  • The table can then be used to look up the output.

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