Decoders and Multiplexers

Digital Logic for Computers

(ACOE161)

Experiment #7

Decoders and Multiplexers

Student’s Name:	Reg. no.:
Semester: Spring 2015	Date: 14 November 2015

Assessment:

Assessment Point	Weight	Grade
Methodology and correctness of results
Discussion of results
Participation
Assessment Points’ Grade:

Comments:

Experiment #7:

Decoders and Multiplexers

Objectives:

The objectives of this experiment are to:

1. use decoders and multiplexers, and

2. to implement larger decoders/multiplexers from smaller ones.

Exercise 1:

(a) Complete Table 1 for a 2-to-4 decoder truth table with the outputs (L0-L3) and enable (E) are active low (0).

Table 1. 2-to-4 decoder truth table with Enable (~G). Active: Low.

E	A	B	L0	L1	L2	L3

(b) The 74LS139 IC contains two (2) 2-to-4 decoders with VCC and GND as shown in Figure 1.

Figure 1. 74LS139 IC contains two (2) 2-to-4 decoders.

(c) Connect the 74LS139 IC on the breadboard and use switches S3/P2, S2/P1, S1/P0 for one set of inputs (~1G, 1A, 1B) and LEDs L0, L1, L2, and L3 to one set of outputs (1Y0, 1Y1, 1Y2, 1Y3). Draw all necessary connections on Figure 2.

Figure 2. 74LS139 IC Dual 2-to-4 decoders.

(d) Using the circuit in Figure 2 go through all the possible states and complete Table 2 below.

Table 2. 74LS139D IC truth table with Enable (E)

E /S3/P2	A /S2/P1	B /S1/P0	L0	L1	L2	L3

(e) Design and draw all the necessary connections to create a 3-to-8 decoder using both 2-to-4 decoders available on the 74LS139 IC and a 7404 IC on Figure 3.

Figure 3. 3-to-8 decoder using 74LS139 IC and 7404 IC.

(f) Complete Table 3 below based on the results of the circuit in Figure 3 for the 3-to-8 decoder.

Table 3. 3-to-8 decoder truth table with Enable (E). Active: Low.

E /S3/P2	A /S2/P1	B /S1/P0	L0	L1	L2	L3	L4	L5	L6	L7

Questions:

1. What is the purpose of the 7404 IC in the implementation of the 3-to-8 decoder in Figure 3?

2. Explain how a 4-to-16 decoder could be implemented using the 74LS139 IC. How many ICs would be required in this case?

Дата добавления: 2015-11-14