Name– Study of basic gates.
Aim – to study the working of basic gates like AND gate, OR gate and NOT gate.
Apparatus – IC 7404, IC 7408, IC 7432, circuit board, power supply +5V DC, LED, connecting wires, soldering iron, cutter etc.
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Procedure –
1) You are given IC 7404, IC 7408 and IC 7432. Identify the ICs by reading their numbers and details from above given pin configurations and specifications.
2) Solder the circuit as shown in the circuit diagram.
3) Connect final output of the circuit to the anode of the LED.
4) Verify the truth table for each type of logic gate by giving different logic inputs.
5) Write the observed truth tables of each gate and hence, write the logic equation of output of each gate.
Brief theory –
1) Definition of AND gate – an AND gate is a logic circuit, whose output becomes high ONLY WHEN ALL ITS INPUTS ARE HIGH. Its logic equation is given by –
Y = A.B
This equation shows that inputs A & B are related to each other with AND mathematical operator. Thus, when A AND B both are high, then only Y is high, otherwise LOW. In this way, the AND multiplication rules for all possible inputs combinations are as follows –
a) When A = B = 0, then Y = A.B = 0.0 = 0
b) When A = 0, B = 1, then Y = A.B = 0.1 = 0
c) When A = 1, B = 0, then Y = A.B = 1.0 = 0
d) When A = B = 1, then only Y = A.B = 1.1 = 1
2) Definition of OR gate – an OR gate is a logic circuit whose output becomes high WHEN ANY ONE OF ITS INPUTS IS HIGH. Its logic equation is –
Y = A + B
This equation shows that inputs A and B are related with OR mathematical operator. Thus, when A OR B is high, Y is high. The OR addition rules for all possible inputs combinations are –
a) When A = B = 0, Y = A + B = 0 + 0 = 0
b) When A = 0, B = 1, Y = A + B = 0 + 1 = 1
c) When A = 1, B = 0, Y = A + B = 1 + 0 = 1
d) When A = B = 1, Y = A + B = 1 + 1 = 1
3) Definition: a NOT gate has only one input and one output. It gives high output WHEN ITS INPUT IS LOW. Its logic equation is –
Y =
Thus, it shows that Y is complement of A. The rules of NOT operations are –
a) When A = 0, then Y = = = 1
b) When A = 1, then Y = = = 0
Note – write observed truth tables on left page of practical record book with pencil only.
Conclusion – it is found that –
1) For an AND gate, when its both inputs = 1, then only its output = 1.
2) For an OR gate, when any one of its inputs = 1, then its output = 1.
3) For a NOT gate, when its input = 1, then its output = 0 and vice versa. Since it inverts the input signal at output, it is also called as inverter.