ECE216 | Exp3 | Understanding the combinational logic using Multiplexer

Aim:

To design a circuit to implement Boolean functions using Multiplexers.

Apparatus required:

Multiplexer ICs (dual 4:1 mux 74153),7404, Chords. 

Learning objectives:

1. How to realize the functionality of Dual 4 Line to 1 Line Multiplexer using 74153 IC. 
2. How Dual 4 Line to 1 Line Multiplexer selects the particular input to be sent to the output. 

Theory:

It quite often happens, in the design of large-scale digital systems, that a single line is required to carry two or more different digital signals. Of course, only one signal at a time can be placed on one line. What is required is a device that will allow us to select, at different instants, the signal we wish to place on this common line. Such a circuit is referred to as a Multiplexer. A multiplexer performs the function of selecting the input on any one of 'n' input lines and feeding this input to one output line.

 Multiplexers are used as one method of reducing the number of integrated circuit packages required by a particular circuit design. This in turn reduces the cost of the system. Assume that we have four lines, C0, C1, C2, and C3, which are to be multiplexed on a single line, Output (Y). The four input lines are also known as the Data Inputs. Since there are four inputs, we will need two additional inputs to the multiplexer, known as the Select Inputs, to select which of the C inputs is to appear at the output. Call these select lines A and B. The gate implementation of a 4-line to 1-line multiplexer is shown below:

Implementation of a Boolean function using 4:1 mux:

Consider the function: In this example, we could have picked any variable to be the data variable and the other two as select variables. Suppose one were to take A as the data variable. The corresponding Karnaugh map is then:

Alternate method:

Implementation of a following function using 4:1 mux: F(A,B,C)=E(1,3,5,6) The given function has three variables. Hence, it can be implemented using a multiplexer with two select inputs and four data inputs. The implementation table of the given function is shown in the table below:

+---+----+-----+-----+-----+
|   | D0 | D1  | D2  | D3  |
+---+----+-----+-----+-----+
| Ā | 0  | (1) |  2  | (3) |
+---+----+-----+-----+-----+
| A | 4  | (5) | (6) |  7  |
+---+----+-----+-----+-----+
|   | 0  |  1  |  A  |  Ā  |
+---+----+-----+-----+-----+

PROCEDURE

1. At first, go through the structure of 74153. Then apply high-level voltage to Vcc and low-level voltage to GND. If Vcc and ground are not connected properly then an error message will be shown and no output will be generated.
2. Next, apply high-level voltage to Strobe1G or strobe 2G. If STROBE 1G is low, 1st Multiplexer is activated. If STROBE 2G is low, then the 2nd Multiplexer is activated.
3. Next, apply low-level voltage to the select inputs A and B (A Most Significant Bit, B Less significant bit). Then apply a high-level voltage to 2C0. Now check that how Dual 4 Line to 1 Line Multiplexer select the particular input to be multiplexed and to be applied to the output IY {1 = 1, 2}.
4. For all the combinations of the select inputs A, B verify that both the LEDs are glowing or not glowing. If the LED glows, it indicates that the corresponding output has reached logic1 level. Similarly, a dark LED indicates a low-level output voltage.
5. If both the Strobe inputs are low then both Multiplexers are activate

Observations:

Results:

Learning Outcomes:

Students will be able to understand the analysis and synthesis of logic

functions with the help of multiplexers.

Cautions:

• Do not press the IC on the breadboard until pins are aligned with pours.
• Make connection properly.
• There should not be any short circuit in the circuit.
• Avoid the heating of IC

. .