Combinational Logic Systems

• Pull up / down resistors ensure that an output is either completely positive or negative, as without a straight connection to the +V or 0V, the output voltage will not be 100% on or off.
• The data sheet of a particular logic gate package shows how the pins are connected to the logic gates inside it.
• There is a shorthand way of writing down the function of logic gates, using a special type of algebra called Boolean algebra.

  • A dot ‘.’ between two input labels is read as AND.
  • A plus ‘+’ between two input labels is read as OR.
  • A bar ‘-’ over the top of an input label is read as NOT.
• NAND gate implementation is used to save space and cost when building a circuit, as only one type of gate is used.
• NAND gate equivalents:

  A) NOT

  B) AND

  C) OR

  D) NOR