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DIET-Dept of ECE Logic gates

Experiment No:

Date:1. LOGIC GATESAIM:To Verify the truth tables of AND, OR, NOT, NAND, NOR, EX-OR logic gates using ICS.APPARATUS:1. Bread board Digital IC trainer kit

1 No.

2. IC 74LS08 (AND)

1 No.3. IC 74LS32 (OR)

1 No.4. IC 74LS04 (NOT)

1 No.5. IC 74LS00 (NAND)

1 No.6. IC 74LS02 (NOR)

1 No.7. IC 74LS86 (EX-OR)

1 No.8. Connecting wires

THEORY:

AND gate: If two or more operands are ANDed, then the result will be logic 1 only if all the operands are 1.A . Sign is used to represent the AND operation. If A and B are the logic operands and Y is the result of the AND operation, then Y is 1(TRUE) only if both A AND B are 1(TRUE). For all other combinations of the inputs, Y is 0(FALSE). The expression for AND operation is given as Y=A. B.

OR gate: If two or more operands are ORed, then the result will be logic 1 if any of the operands is a logic1. A + Sign is used to represent the OR operation. If A and B are the logic operands and Y is the result of the OR operation, then Y is 1(TRUE) if either A OR B is 1 (TRUE). Y is 0 (FALSE) only when both A and B are 0. The expression for OR operation is given as Y=A + B.

NOT gate: The NOT operation corresponds to complementing the input variable. In this there could be only one input and one output and the output is NOT the input. If the input is 1 (TRUE) then the output is 0 (FALSE) and if the input is 0, the output is 1. The NOT operation is given by the expression Y = .

NAND gate: NAND gate is the gate indicating NOT AND i.e., the output of the NAND gate will be the complement of the output of the AND gate. This is shown in the table 1.1. In the table, A and B are the inputs, Y corresponds to the output of an AND gate and Y corresponds to the output of a NAND gate. It can be seen that the output of the NAND gate is the complement of that of the AND gate. The NAND operation is given by the expression NOR gate: NOR gate is the gate indicating NOT OR i.e., the output of the NOR gate will be the complement of the output of the OR gate. This is shown in the table 1.1. In the table, A and B are the inputs, Y corresponds to the output of an NOR gate. It can be seen that the output of the NOR gate is the complement of that of the OR gate. The NOR operation is given by the expression

X-OR gate: The X-OR logic is different from other gates whose output is one, only when the applied inputs are different i.e., it is an odd function and is one when it contains odd number of ones.

So, at A=0, B=1 or A=1, B=0 the output of X-OR is 1.CIRCUIT DIAGRAMS:

TRUTH TABLES AND OBSERVATION TABLES:

Table 1.1: Truth tables and observation tables for logic gatesPROCEDURE:1. +5V DC is applied at Vcc (pin no 14) of each IC w.r.t ground (pin no7).

2. I/Ps are applied (at pin nos l&2) and output is taken from (pin no 3).

3. I/Ps are applied from toggle switches and o/p is observed at o/p indicators.PRECAUTIONS:1. The open circuit voltage of the power supply must be stable and close to 5V.

2. Correct components should be connected on the bread board with proper polarities.

3. A multimeter reading greater than VDD indicates an open connection in the circuit. Verify the circuit before proceeding.

4. Use multimeter probe tip to gently ease the IC out of breadboard. The mid-section groove of the breadboard can be used to gently lift the IC. Using bare hands might cause IC pins to break.

5. In case the logic gate outputs do not make sense, check your circuit thoroughly. If the problem is still not resolved, get the IC tested by the technician.

RESULT:Verified the truth tables of AND, OR, NOT, NAND, NOR, EX-OR gates using ICS.VIVA QUESTIONS1) What changes should be made in the above circuits for negative logic?

2) Explain how NOT gate acts as inverter?

3) Draw IEEE rectangular shape symbols for logic gates.

4) How is average power dissipation in a logic gate calculated?

5) Define noise margin. Draw a visual representation of noise margin idea.* * * * *

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