There are 5 basic elements Logic elements: And, Or, Not, Nand and Nor.

There is a short Summary and Test at the end
This is how they operate.... The lamp indicates the output.

Close both Sw1 and Sw2 to light lamp		An And element is called an AND Gate. InputsOutputs
Close Sw1 or Sw2 to light lamp		An Or element is called an OR Gate. Inputs Outputs
Closing Sw1 does NOT light the lamp IE: close Sw1 to turn the lamp off		A Not function is called an INVERTER. call the small circle a Knot to remember it.

How And, Or and Not Gates work

no voltage at inputs no voltage at outputs AND Gate	voltage at either input no voltage out	voltage at both inputs voltage out
voltage at lower input voltage out OR Gate	voltage at upper input voltage out	voltage at both gates voltage out
no voltage here voltage out INVERTER	voltage here no voltage out	The 2 logic numbers 0 = no voltage 1 = voltage The function of the three gates can be expressed in logic numbers

0 0 0	0 1 0	1 0 0	1 1 1
0 0 0	1 0 1	0 1 1	1 1 1
0 1	1 0

The numbers 0 and 1 are called logic values. Each gate can have 2 possible values. TRUE for logic level 1 and FALSE for logic level 0. THUS we can make a TRUTH table for each of the gates.
 

Truth Table	Translates to	Truth Table	Translates to
AND Gate Inputs Output 0 0 0 0 1 0 1 0 0 1 1 1	Inputs Outputs 1 1 1 any other input 0	OR Gate Inputs Output 0 0 0 0 1 1 1 0 1 1 1 1	Inputs Outputs 0 0 0 any other input 1

 

Truth Table	Translates to
NOT Gate Input Output 0 1 1 0	Cannot be simplified further!

Truth Table	Translates to	Truth Table	Translates to
Nand Gate Inputs Output 0 0 1 0 1 1 1 0 1 1 1 0	Inputs Outputs 1 1 0 any other input 1	Nor Gate Inputs Output 0 0 1 0 1 0 1 0 0 1 1 0	Inputs Outputs 0 0 1 any other input 0

For an OR gate:

A voltage at one input will change the output and the other input will have no effect.

For an INVERTER:

The output is of opposite logic level to the input.

For A NAND gate:

A voltage on one input will have no effect but a voltage at both inputs will change the state of the output.

For a NOR gate;

A voltage at either input will change the output.

TEST

Answer these questions:

1. Name the 4 commonly used types of gates:

2. What is the common name for a NOT gate?

3. What are the two TRUTH values?

4. Look at the four TRUTH tables to answer these...

   A: With one gate of an AND GATE at logic 1 will the other gate alter the output?
   B: With one gate of an OR GATE at logic 1 will the other gate alter the output?
   C: With one gate or a NAND GATE at logic level 1 will the other gate alter the output?
   D: With one gate of a NOR GATE at logic level 1 will the other gate alter the output?

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