IC 74151 PDF

IC Necessity of multiplexers:. Types of MUX:. It has eight data inputs D0 to D7, three select inputs S0 to S2, an enable input and one output. Fig: MUX using gates. Ex: Implement the following Boolean function using multiplexer.

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Multiplexing is the property of combining one or more signals and transmitting on a single channel. This is achieved by the device multiplexer.

A multiplexer is the most frequently used combinational circuits and important building block in many in digital systems. These are mostly used to form a selected path between multiple sources and a single destination. A basic multiplexer has various data input lines and a single output line.

These are found in many digital system applications such as data selection and data routing, logic function generators, digital counters with multiplexed displays, telephone network, communication systems, waveform generators, etc.

In this article we are going to discuss about types of multiplexers and its design. The multiplexer or MUX is a digital switch, also called as data selector.

It is a combinational circuit with more than one input line, one output line and more than one select line. It allows the binary information from several input lines or sources and depending on the set of select lines , particular input line , is routed onto a single output line.

The basic idea of multiplexing is shown in figure below in which data from several sources are routed to the single output line when the enable switch is ON. The below figure shows the block diagram of a multiplexer consisting of n input lines, m selection lines and one output line. If there are m selection lines, then the number of possible input lines is 2m. For example, if one of the 4 input lines has to be selected, then two select lines are required.

Similarly, to select one of 8 input lines, three select lines are required. Generally the number of data inputs to a multiplexer is a power of two such as 2, 4, 8, 16, etc. Some of the mostly used multiplexers include 2-to-1, 4-to-1, 8-to-1 and to-1 multiplexers. These multiplexers are available in IC forms with different input and select line configurations. Depends on the select signal, the output is connected to either of the inputs.

Since there are two input signals only two ways are possible to connect the inputs to the outputs, so one select is needed to do these operations. If the select line is low, then the output will be switched to D0 input, whereas if select line is high, then the output will be switched to D1 input. The figure below shows the block diagram of a 2-to-1 multiplexer which connects two 1-bit inputs to a common destination.

The truth table of the 2-to-1 multiplexer is shown below. Depending on the selector switching the inputs are produced at outputs , i. From the above output expression, the logic circuit of 2-to-1 multiplexer can be implemented using logic gates as shown in figure. Thus, the output generated by the OR gate is equal to D0. Therefore, the output of the OR gate is D1. Thus, the above given Boolean expression is satisfied by this circuit.

In some cases, two or more multiplexers are fabricated on a single IC because simple logic gates can implement the multiplexer. Generally four 2 line to 1 line multiplexers are fabricated in a single IC as shown in figure below. The selection line controls the input lines to the output in all four multiplexers. The control input E enables and disables all the multiplexers, i.

The select lines S1 and S2 select one of the four input lines to connect the output line. The particular input combination on select lines selects one of input D0 through D3 to the output. The figure below shows the block diagram of a 4-to-1 multiplexer in which the multiplexer decodes the input through select line. The truth table of a 4-to-1 multiplexer is shown below in which four input combinations 00, 10, 01 and 11 on the select lines respectively switches the inputs D0, D2, D1 and D3 to the output.

To get the total data output from the multiplexer, all these product terms are to be summed and then the final Boolean expression of this multiplexer is given as. From the above expression of the output, a 4-to-1 multiplexer can be implemented by using basic logic gates. In this circuit, each data input line is connected as input to an AND gate and two select lines are connected as other two inputs to it.

Generally, this type of multiplexers is available in dual IC forms and most common type is IC which is a dual 4-to-1 line multiplexer. It consists of two identical and independent 4-to-1 multiplexers.

Usually, the enable input or strobe can be used to cascade two or more multiplexer ICs to construct a multiplexer with large number of inputs. Each multiplier is supplied with separate inputs. The figure below shows the pin diagram of IC An 8-to-1 multiplexer consists of eight data inputs D0 through D7, three input select lines S2 through S0 and a single output line Y.

Depending on the select lines combinations, multiplexer decodes the inputs. The below figure shows the block diagram of an 8-to-1 multiplexer with enable input that enable or disable the multiplexer. The truth table for an 8-to1 multiplexer is given below with eight combinations of inputs so as to generate each output corresponds to input. Similarly the data outputs D0 to D7 will be selected through the combinations of S2, S1 and S0 as shown in below figure.

From the above Boolean equation, the logic circuit diagram of an 8-to-1 multiplexer can be implemented by using 8 AND gates, 1 OR gate and 7 NOT gates as shown in below figure. In the circuit, when enable pin is set to one, the multiplexer will be disabled and if it is zero then select lines will select the corresponding data input to pass through the output.

A typical IC is an 8-to-1 multiplexer with eight inputs and two outputs. The two outputs are active low and active high outputs. It has three select lines A, B and C and one active low enable input. The pinout of this IC is given below. In all types of digital system applications, multiplexers find its immense usage.

Since these allows multiple inputs to be connected independently to a single output, these are found in variety of applications including data routing, logic function generators, control sequencers, parallel-to-serial converters, etc.

Multiplexers are extensively used in data routing applications to route the data to a one particular destination from one of several sources. One of the applications includes the displaying of two multidigit BCD counters, one at a time. In such application, multiplexer ICs are used to select and display the content of either of two BCD counters using a set of decoder and LED displays. In place of logic gates, a logical expression can be generated by using a multiplexer.

It is possible to connect the multiplexer such that it duplicates the logic of any truth table. In such cases it can generate the Boolean algebraic function of a set of input variables. This abruptly reduces the number of logic gates or integrated circuits to perform the logic function since the multiplexer is a single integrated circuit.

In this kind of applications, multiplexers are viewed as logic function generators. For example consider the below logic diagram to implement the ex-OR function of three inputs. A A 8-to-1 multiplexer is used in this logic generator. This multiplexer works exactly similar to the set of logic gates implementing the same function. The output F is 1 for data inputs D1, D2, D5 and D6 which are selected by making selection lines to , , and respectively.

A multiplexer circuit can be used to convert the parallel data to serial data , so as to reduce parallel buses to serial signals. In digital systems, mostly data processed in parallel for achieving higher speeds. But for transmission of the data signals over long distances need more number of lines to process the data.

In such cases parallel data is converted into serial form using multiplexers. The figure below shows the parallel to serial data conversion using an 8 input multiplexer.

Parallel data from the data in or some other register is applied to the 8 input lines of the multiplexer. The selection codes for the multiplexer are generated by a 3-bit counter. With the application of each clock pulse to the counter the data is serially out from the multiplexer. Other applications of multiplexers include control sequencers, pulse train generators, encoders, register to register data transfer, waveform generators, etc. Your email address will not be published.

Table of Contents. Comments can u explain 16 to 1 multiplexer. Great explanation! Finally i understand this logic gate in depth. Leave a Reply Cancel reply Your email address will not be published.


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