Logic gates
In its most basic form, a computer is a collection of powered and unpowered A closed loop through which current moves - from a power source, through a series of components, and back into the power source. and Microscopic devices that open and close circuits to communicate electrical signals. CPUs contain millions of transistors.. A Circuit components which take several inputs, compare the inputs with each other, and provide a single output based on logical functions such as AND, OR and NOT. is a series of transistors connected together to give one or more Data which is sent out of a system., each output being based on the Data which is inserted into a system for processing and/or storage. or combination of inputs supplied to it. There are three types of gate to consider:
- AND gate
- OR gate
- NOT gate
Each type of gate can be represented either as a diagram, in algebraic form, or as a A table to list the output for all possible input combinations into a logic gate..
AND gates
An AND gate uses two inputs to generate one output. The output is 1 (TRUE) only if both of the inputs are 1 (TRUE).
AND gates are represented diagrammatically as:
A represents the first input. B represents the second input. Q represents the output.
A truth table shows, for each combination of inputs, what the output will be. Like logic gates, a 0 in the table represents FALSE, while 1 represents TRUE.
An AND gate is represented in the truth table below.
| A | B | Q |
| 0 | 0 | 0 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 1 |
| A | 0 |
|---|---|
| B | 0 |
| Q | 0 |
| A | 0 |
|---|---|
| B | 1 |
| Q | 0 |
| A | 1 |
|---|---|
| B | 0 |
| Q | 0 |
| A | 1 |
|---|---|
| B | 1 |
| Q | 1 |
OR gates
An OR gate uses two inputs to generate one output. The output is 1 (TRUE) only if either or both of the inputs are 1 (TRUE).
OR gates are represented diagrammatically as:
A represents the first input. B represents the second input. Q represents the output.
An OR gate is represented in the truth table as below.
| A | B | Q |
| 0 | 0 | 0 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 1 |
| A | 0 |
|---|---|
| B | 0 |
| Q | 0 |
| A | 0 |
|---|---|
| B | 1 |
| Q | 1 |
| A | 1 |
|---|---|
| B | 0 |
| Q | 1 |
| A | 1 |
|---|---|
| B | 1 |
| Q | 1 |
NOT gates
A NOT gate uses just one input to generate one output. A NOT gate inverts the input - the output is 1 (TRUE) if the input is 0 (FALSE), and the output is 0 (FALSE) if the input is 1 (TRUE).
NOT gates are represented diagrammatically as:
The NOT gate has what appears to be a nose at the front. When using more complex gates, this nose is added to other gates to show they have been combined with the NOT gate.
A NOT gate is represented in the truth table below.
| A | Q |
| 0 | 1 |
| 1 | 0 |
| A | 0 |
|---|---|
| Q | 1 |
| A | 1 |
|---|---|
| Q | 0 |