Digital Logic for Computers

ACOE161: / Digital Logic for Computers / Experiment # 1

Digital Logic for Computers

(ACOE161)

Experiment #1

Basic Logic Gates

Student’s Name:
Semester: / Date:

Assessment:

Assessment Point / Weight / Grade
Methodology and correctness of results
Discussion of results
Participation

Assessment Points’ Grade:

Comments:

Experiment #1:

Basic Logic Gates

Objectives:

The objectives of this experiment are to:

introduce students in the tools, facilities and components needed for the experiments in digital electronics,
relate voltage levels and electrical connections to digital logic levels, and
verify the operation of the basic logic gates.

Discussion:

Digital electronics are built using logic gates. Each logic gate implements a logic function such as the NOT (also known as the inverter), the AND, the OR and the Exclusive OR (also known as the EX-OR gate). In some cases the output of a gate is internally inverted. The AND gate with the output inverted is called the NAND gate. The OR gate with the output inverted is called the NOR gate. The EX-OR gate with
the output inverted is called the EX-NOR gate.

Figure 1: Basic Logic Gates

Figure 1 shows the basic logic gates. Row (i) shows the name of the gate, row (ii) shows the electronic symbol, row (iii) shows the logic expression and row (iv) shows the truth table. A truth table is a table showing all possible values at the inputs of a digital circuit and the corresponding value of the output.

Procedure:

Exercise 1:

(a)Place the 7404 and the 7408 ICs on the breadboard and make the connections shown in figure 2. Turn on the Digital Lab Trainer power.

Figure 2.

(b)With the aid of a voltmeter, a logic probe and the LED monitors on the Digital Lab Trainer, record the state of the pins 1, 2, 3, 4, 12 and 13 of the 7404, and hence fill up table 1.

Pin 1 / Pin 2 / Pin 3 / Pin 4 / Pin 12 / Pin 13
Voltage (volts)
Logic Probe (H,L, Z)
Led (ON, OFF) / L6: / L7: / L5:

Table 1.

(c)Move the switch S7 to positions “0” and “1” and record the state of pins 10 and 11 of the 7408 in table 2.

Pin 10 / Pin 11 / S6 / S5 / L3
S7 = “0” / S7 = “1” / S7 = “0” / S7 = “1” / 0 / 0
Voltage (volts) / 0 / 1
Logic Probe (H,L,Z) / 1 / 0
Led (ON, OFF) / L4: / L4: / 1 / 1
Table 2. / Table 3.

(c)Go through all possible states of the switches S6 and S5 and fill up table 3.

Exercise 2:

(a)Turn off the Digital Lab Trainer power. Place the 7432 and the 7486 ICs on the breadboard and make the connections shown in Figure 3. Turn on the Digital Lab Trainer power.

Figure 3.

(b)Go through all possible states of the switches S7, S6, S5 and S4 and fill up table 4. Use number 1 to represent the ON state of the LEDs and number 0 to represent the OFF state.

S7 / S6 / L7 / S5 / S4 / L6
0 / 0 / 0 / 0
0 / 1 / 0 / 1
1 / 0 / 1 / 0
1 / 1 / 1 / 1
(a) / (b)

Table 4.

Exercise 3:

(a)Turn off the Digital Lab Trainer power. Place the 7400 and the 7402 ICs on the breadboard and make the connections shown in Figure 4. Turn on the Digital Lab Trainer power.

Figure 4.

(b)Go through all possible states of the switches S7, S6, S5 and S4 and fill up table 5. Use number 1 to represent the ON state of the LEDs and number 0 to represent the OFF state.

S7 / S6 / L7 / S5 / S4 / L6
0 / 0 / 0 / 0
0 / 1 / 0 / 1
1 / 0 / 1 / 0
1 / 1 / 1 / 1
(a) / (b)

Table 5.

Questions

Discuss the results of exercise 1 (Table 1, Table 2 and Table 3)

What is the voltage and logic level at pin 8 of the 7408 (pins 9 and 10 are open).

Discuss the results of exercise 2 (Table 4)

Discuss the results of exercise 3 (Table 5)