EE101 - Digital Electronics Laboratory

Laboratory Exercise 2. The NOT, NAND and NOR Gates

Objectives:

	To investigate NOT, NAND and NOR gate operation.
	To study some the laws associated with the NOT, NAND and NOR operations.
	To investigate De Morgan's Theorem

Introduction

This is the second laboratory session, to allow you to become familiar with some more gates and the rules associated with them.

The demonstrator may quiz you on your knowledge of the Laboratory Manual.

Equipment

The equipment you require is as follows:

	Your lab notebook
	Your own lab kit (bought from the technicians).
	Minilab set, including Digital voltmeter (available at the desks)
	Collect hook-up wire and ICs from demonstrator. (NOT gate, NAND gate, NOR gate, AND gate, OR gate)

Pre-Laboratory

There are several tasks that you must perform prior to sitting this laboratory:

	Read the laboratory assignment in full.
	What is the relationship between the input and output of a NOT gate?
	Describe the NAND and NOR operation in your own words.
	Can any logic operation be performed using NAND gates? How?
	Can any logic operation be performed using NOT gates? How?
	State De Morgan's Theorem
	Draw up the truth table for a 2-input Exclusive-OR gate.

Useful Chip Diagrams:

7404(NOT) 7400(NAND) 7402(NOR)

The Laboratory:

Section 1. NOT Gate Implementation

(a) Connect one of the NOT gates (74LS04) as shown in Figure 1. Remember to power the Vcc and GND terminals of the chip. Remember also to leave the MiniLab turned off, until you are sure that your circuit is wired correctly.

Figure 1. The NOT gate

(b) Vary the input A (i.e. 0 and +5V) to obtain all the possible combinations and complete the Truth table for the NOT gate. Measure the output F using a Digital Voltmeter. Give the exact voltages that you obtained for each state of the gate.

(d) Connect an AND gate and inverter as shown in Figure 2 to generate A./A.

Figure 2. Circuit of equation A./A

Change the states of A to note the effects. Describe what happens.

(e) Create a logic diagram to prove /A + A = 1. Implement this circuit and prove the law. Describe what happens in your circuit.

Section 2. De Morgan's Theorem

(a) Connect inputs A and B and their complements /A and /B to AND, OR gates as shown in Figure 3. You will have to use NOT gates to obtain these states.

Figure 3. Proving De Morgan's Theorem.

(b) Vary inputs A and B and enter the output values into a truth table as show below. Also, what is the Boolean equation for F and G in terms of A and B?

A	B	F	G
0	0
0	1
1	0
1	1

What is the minimised equation. Implement the equation above and compare it to your minimised version.

Section 3. The implementation of the NAND gate.

(a) Connect one of the 2-input NAND gates as shown in Figure 4.

Figure 4. The NAND gate.

Enter the output values into a truth table as show below. Vary the inputs and record the output of the gate F and the actual voltage V. Examine the output of the NAND gate when one of the inputs is left floating (not connected). How can a NAND gate be used as an inverter?

A	B	F	V (actual voltage)
0	0
0	1
1	0
1	1

Section 4. The implementation of the NOR gate.

(a) Connect the NOR gate as shown in Figure 5.

Figure 5. The NOR gate.Enter the output values into a truth table as show below. Vary the inputs and record the output of the gate F and the actual voltage V. Examine the output of the NOR gate when one of the inputs is left floating (not connected). How can a NOR gate be used as an inverter? Check your last answer on the breadboard.

A	B	F	V (actual voltage)
0	0
0	1
1	0
1	1

Section 5. Basic NAND gate operations

(a) Connect up NAND gates to perform the AND operation. Connect up NAND gates to perform the OR operation. How did you do this? Describe your outputs. Can any gate be created using NAND gates?

Section 6. Analysis of Results

(a) A./A equals

         1
         0
         Don't Know

(b) The internal circuitry of the AND gate interprets an open input as a:

         1
         0
         Don't Know

         F = A
         F = B
         F = /(A.B)
         Other answer.

(d) OR gates interpret disconnected inputs as a:

         1
         0
         Don't Know

(e) A.(/A+B) equals:

         AB
         A+B
         A
         B
         Something else

(f) (A+B).(A+/B) equals

         AB
         A+B
         A
         Something else

(g) A.B + B./A + A.C equals:

         B + A.C
         A.B + A.C + /B.A
         /B./C + A
         Something else

(h) A.B + A./B equals:

         AB
         A+B
         A
         Something else

Section 7. Conclusions

(a) State briefly, but clearly, what you have gained from this laboratory. Outline aspects that you have noted within the experiment outside of the questions asked. Make comments on the procedure of the lab - Is there anything that you could have done differently? How did you split the work between group members? Did you have a plan of action? What else would you suggest that should be added to this lab session?

(b) Comments: Please write any comments that you may have here. Did you enjoy the lab? State one thing you would change? State one thing that you liked? Were there any problems during the laboratory session?

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