Chapter 3- Logic Circuits

Chapter 3- Logic Circuits

1. Logic Gates

   • Take binary inputs and produce a binary output
     • Control sensory electronic circuits
   • NOT Gate
     • Output is the opposite of the input
   • AND Gate
     • Output is 1 if both Inputs are 1
   • OR Gate
     • Output is 1 if either or both inputs are 1
   • NOR Gate
     • Output is 1 if neither input is 1
   • NAND Gate
     • Output is 1 if not both inputs are 1
   • XOR Gate
     • Output is 1 if inputs are opposites
   • Number of possible outputs is equal to 2^The number of inputs
     • 1 input has 2 outputs
     • 4 inputs has 16 outputs

2. Logic Circuits

   • Several logic gates combine to create a logic circuit
     • These circuits are designed to carry out specific functions
       • Opening a window in a greenhouse depending on the humidity
       • Turning off the lights in a house when the natural light intensity reaches a threshold value
       • Conrolling a robot depending on the surroundings
       • Turns on a heater if the temperature drops below a threshold value
   • Checking of the output from a logic circuit is done using a truth table
     • Truth tables trace the output from a logic gate or circuit by listing all possible inputs
   • Electronic circuits work on making decisions
     • Need logic gates to make decisions based on inputs

3. Companies will decide between using

   • Off the shelf logic gates and building up a circuit eg just using the NAND gate we could create the AND, OR and the NOT gate
   • Simplifying the logic circuit by using more advanced gates eg using XOR, XAND and XOR gates to reduce size of the logic circuit

4. Use

   • We can design a logic circuit given a logic statement
     • Create the logic statement and then construct the circuit in parts and then create the truth table
   • We can design a logic circuit to carry out a function
     • Convert information given into logic statements, produce circuits and then produce the truth table
   • Produce a truth table from a logic circuit
     • Split the logic circuit into parts and follow the output from part 1 to the end and then create a truth table

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