AND, OR, NOT Gates

AND, OR, NOT Gates

1. A NOT gate has one input and one output, it inputs binary and convert them to their opposite, for example it would turn a '0' into a '1' and vise versa.

2. An AND gate has two inputs and one output. Both inputs must be 1 if the AND gate is to output 1 otherwise it will output a 0 as show in the picture with the truth table.

   • An easier way to understand how AND gates work is to think of it as "If input A AND input B are 1 then output 1 otherwise output a 0."

3. An Or gate is like an AND gate in the sense of its inputs and outputs however what happens to the binary that goes through them is different. If both inputs are '0' then it will output a '0' otherwise it will output a '1' as shown by the truth table.

   • An easier way to understand how OR gates work is to think of it as "If input A OR input B are 1 then output 1 otherwise output 0."

4. The Inputs on AND,OR and NOT gates are usually labelled A,B,C,D and so on, whereas the outputs are labelled P,Q,R,S etc.

   • When writing truth tables, the best way of finding out all the possible outputs is to write the pattern of 0,1,0,1 on the Furthest collum, then on the collum next to that do the same pattern but double the 0's and 1's for example it would be 0,0,1,1. Then do the same pattern but double again so it would be 0,0,0,0,1,1,1,1 keep do this until the table is filled and you should have all the possible outcomes.

5. Gates can have outputs that lead directly into other gates. Using words, this is displayed in brackets. The gates in brackets come first. For example the expression for the picture above would be: P = (A AND B) OR C.

   • TIP: It's best when writing the equations to gates that you start from the end and work your way to the beginning.

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