Hello dear Students,
Below are some notes on Logic Gates. We have covered this part in today's class. So please understand the notes and share your understanding with your peers.
Logic gates
Digital systems are said to be constructed by using logic gates which are the elementary building block of a digital circuit.
Logic gates process signals which represent true or false. Normally the positive supply voltage +5Vs represents true (1) i.e. the high state and 0V represents false (0) i.e. the low state.
The logic state of a terminal can, and generally does, change often, as the circuit processes data.
Most logic gates have at least two inputs and one output. At any given moment, every terminal is in one of the two binary conditions low (0) or high (1), represented by different voltage levels.
Truth tables
A truth table is a good way to show the function of a logic gate. It shows the output states for every possible combination of input states. The symbols 0 (false) and 1 (true) are usually used in truth tables.
The AND gate
The AND gate is an electronic circuit that gives a high output (1) only if all its inputs are high. The AND gate is so named because, if 0 is called "false" and 1 is called "true," the gate acts in the same way as the logical "and" operator.
A dot (.) is used to show the AND operation i.e. A.B (Bear in mind that this dot is sometimes omitted i.e. AB)
The OR gate
The OR gate is an electronic circuit that gives a high output (1) if one or more of its inputs are high (true). If all the inputs are low (false) then the output is low (false). A plus (+) is used to show the OR operation. The OR gate gets its name from the fact that it behaves after the fashion of the logical inclusive "or".
The NOT gate
The NOT gate is an electronic circuit that produces an inverted version of the input at its output. It is different from other electronic gates; it has only one input and one output. It is also known as an inverter. It reverses the logic state.
If the input variable is A, the inverted output is known as NOT A. This is also shown as A', or A with a bar over the top, as shown at the outputs.
