CH 03 : Logic Gates And Logic Circuits

Logic Gates

• ==Logic Gates==: They take binary inputs and give binary outputs in an electronic circuit.

• ==Truth Table:== A table used to check the outputs from a logic gate or logic circuit.

  • All possible combinations of binary inputs are considered in a Truth Table.

• The six different types of Logic Gates are as follows:

• ==NOT Gate==: Has only one input and output is 1 only if input is 0.

  

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  • Truth Table:

• ==AND Gate==: Two inputs. Output is 1 if both inputs are 1s.

  

  • Truth Table:

• ^^Tip: Multiply the inputs.^^

  

• ==OR Gate==: Two inputs. Output is 1 when any of the inputs is 1.

  

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  • Truth Table:

• ^^Tip: Add the inputs.^^

  

• ==NAND (NOT AND) Gate==: Two Inputs. Output is 1 if both inputs are not 1.

  

  • Truth Table:

• ^^Tip: Calculate for AND and write opposite output.^^

  

• ==NOR (NOT OR) Gate:== Two inputs. Output is 1 if neither input is 1

  

  • Truth Table:

• ^^Tip: Calculate for OR and write opposite.^^

  

• ==XOR Gate==: Two inputs. Output is 1 if inputs are not same.

  

  • Truth Table:

Logic Circuits

• Multiple Logic gates make up a ==Logic Circuit.==

• Complex operations are performed through them.

• Truth tables are made to check outputs, and all inputs are considered.

• To make a truth table, it is easier to divide the circuit into parts and name all the outputs at each stage.Example:

  

• In order to make a Logic Circuit from a Logic statement, mark all the gates in the statement, and always mind the brackets.

• To make a logic circuit from Boolean or Logic statements, make different parts of the circuit and then join them using gates which connect the brackets.

• Some logic gates can make a whole logic circuit and any other logic gate. They are known as ==Building Blocks==. NAND gate, for example, can make an AND gate:

  

• Logic circuit can also be simplified. Just like the circuit above can be simplified to just one AND gate.

• Note: When one input branches into two before entering a gate, the two branched inputs will ^^always^^ be same. 1,1 or 0,0.

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