The document discusses NOR gates and their universality. NOR gates are universal gates, meaning they can be combined to form any other logic gate. For example, an AND gate can be implemented using four NOR gates in series, and an OR gate can be implemented using three NOR gates. The document describes an experiment using NOR gates with LED outputs to verify the truth table for a NOR gate circuit. It summarizes that the LED outputs matched the expected outputs in the truth table, demonstrating the functionality of the NOR gate.

1. Experiment No 4
INTRODUCTION TO UNIVERSALITY OF GATES
Objective:
To study the Characteristics and Universality of NOR gate.
Apparatus:
 DC power supply
 Breadboard
 Connecting wires
 LED
 Resistor
Theory:
A logic gate is just a simple Boolean function, which means that it has only either of two outputs. Either 1 or
0, high or low, true or false, whatever you can call it. It is the most elementary tool in building a circuit. A
logic gate performs a logical operation on an input and gives the appropriate output for it.
A NOR gate is a logic gate which gives a positive output only when both inputs are negative. Like NAND
gate, NOR gates are so-called "universal gates" that can be combined to form any other kind of logic gate. For
example, the first embedded system, Apollo Guidance Computer, was built exclusively from NOR gates,
about 5,600 in total for the later versions. Today, integrated circuits are not constructed exclusively from a
single type of gate
Fig 4.1
NORis a combination of OR gate and NOTgate are the output of the OR gate. It is represented as 𝐀 + 𝐁̅̅̅̅̅̅̅̅. The
figure 4.1 is of a two input NOR gate. The first part is an OR gate and second part is a dot after it represents a
NOT gate. So it is clear that during the operation of NORgate, the inputs are first going through OR gate and
after that, the output gets reversed, and we get the final output.
The three main ways of specifying the function of combinational logic circuits are:
1. BooleanAlgebra – This forms the algebraic expression showing the operation of logic circuit for
each input variable either TRUE or FALSE the results in a logic “1” output.
2. Truth Table – A truth table defines the function of logic gate by providing a concise list that shows
all the output states in tabular form for each possible combination of output variable that the gate could
encounter.
3. Logic Diagram – This is a graphical representation of a logic circuit that shows the wiring and
connection of each individual logic gate, represented by a specific graphical symbol that implements
the logic circuit.

2. Universal Gate:
A universal gate is a gate which can implement any Boolean function without need to use any other gate type.
The NAND and NOR gates are universal gates. In practice, this is advantageous since NOR gates is
economical and easier to fabricate and is the basic gate used in all IC digital logic families.
2-input NOR Gate
Input Output
Fig 4.2
Inputs Output
A B 𝐀 + 𝐁̅̅̅̅̅̅̅̅
0 0 0
0 1 1
1 0 1
1 1 1
Table 4.1
As combinational logic circuits are made up from individual logic gates only, they can also be considered as
“decision making circuits” and combinational logic is about combining logic gates together to process two or
more signals in order to produce at least one output signal according to the logical function of each logic gate.
Solid state switches come in a variety of different types and ratings, and there are many different applications
for using solid state switches.
Fig 4.3

3. Implementing AND using only NOR Gates
AND gate can be replaced by using four NOR gates in series as shown in figure 4.4
Fig 4.4
Implementing OR Gate only using NOR Gates
The OR gate can be replaced by using three NOR gates as shown in figure 3.4.
Fig 4.5
Thus the NOR gate is a universal gate since it can implement the AND, OR and NOT functions.
Circuit Diagram:
Fig 4.6
Procedure:
1. We issued apparatus from lab instructor. We connected the circuit and DC power supply.
2. We biased the ICs e.g; Vcc and GRD, and do necessary connections for input and output.
3. We provided it Vcc at 14 and GRD on pin 7.

4. 4. We make the combine circuits of two basic gates.
5. Turn ON the circuit and give various combination of inputs with the help of switches.
6. Note output with the help of LED, we verified our output from the Table 4.2.
Truth Table:
A B C D 𝐴̅ 𝐵̅ 𝐶̅ D̅ 𝐴̅ + 𝐵̅ 𝐶̅+ 𝐷̅ 𝐴̅ + 𝐵̅̅̅̅̅̅̅̅̅ 𝐶̅ + 𝐷̅̅̅̅̅̅̅̅̅ 𝐴̅ + 𝐵̅̅̅̅̅̅̅̅̅ + 𝐶̅ + 𝐷̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅
0 0 0 0 1 1 1 1 1 1 0 0 0
0 0 0 1 1 1 1 0 1 1 0 0 0
0 0 1 0 1 1 0 1 1 1 0 0 0
0 0 1 1 1 1 0 0 1 0 0 1 1
0 1 0 0 1 0 1 1 1 1 0 0 0
0 1 0 1 1 0 1 0 1 1 0 0 0
0 1 1 0 1 0 0 1 1 1 0 0 0
0 1 1 1 1 0 0 0 1 0 0 1 1
1 0 0 0 0 1 1 1 1 1 0 0 0
1 0 0 1 0 1 1 0 1 1 0 0 0
1 0 1 0 0 1 0 1 1 1 0 0 0
1 0 1 1 0 1 0 0 1 0 0 1 1
1 1 0 0 0 0 1 1 0 1 1 0 1
1 1 0 1 0 0 1 0 0 1 1 0 1
1 1 1 0 0 0 0 1 0 1 1 0 1
1 1 1 1 0 0 0 0 0 0 1 1 1
Table 4.2
Conclusion:
The above table is verified and at output “1” the LED goes to lighten otherwise it shows no light.
Precautions:
 Ground and potential positions should be adjusted the accurately
 When disassembling a circuit, first remove the source of power.
 When unplugging a power cord, pull on the plug, not on the cable.
 When making measurements, form the habit of using only one hand at a time. No part of a live circuit
should be touched by the bare hand.