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What is Multiplexer?
A multiplexer is a combinational circuit that obtains binary data from one of 2" input data lines and manages it to an individual output line. The selection of a specific input data line for the output is decided by a collection of selection inputs. A 2"-to-1 multiplexer has 2" input data lines and n input selection lines whose bit combinations decide which input data are chosen for the output.
A 4-to-1-line multiplexer is demonstrated in the figure. Each of the four data inputs I0 through I3 is used to one input of an AND gate. The two selection inputs S1 and S0 are decoded to choose a specific AND gate. The outputs of the AND gates are used to a single OR gate to offer the single output. It can show the circuit operation, suppose the case when S1S0 = 10.
The AND gate related to input I2 has two of its inputs similar to 1. The third input of the gate is linked to I2. The other three AND gates have a minimum of one input similar to 0. It can create outputs similar to 0. The OR gate output is now similar to the value of I2. It can be supporting a direction from the selected input to the output.
The 4-to-1 line multiplexer of the diagram has six inputs and one output. A truth table representing the circuit requires 64 rows during six input variables that can have 26 binary combinations. This is an extremely long table and will not be demonstrated here. A more efficient method to define the operation of multiplexers is using a function table.
The function table for the multiplexer is demonstrated in the table. The table shows the relationship between the four data inputs and the single output as a function of the selection inputs S1 and S0.
When the selection inputs are similar to 00, output Y is similar to input I0 When the selection inputs are similar to 01, input I1 has a direction to output Y, and equally for the other two combinations. The multiplexer is also known as a data selector. It can choose one of many data inputs and drive the binary data to the output.
The function table for a 4 * 1 Multiplexer can be represented as −
| S1 | S0 | Y |
|---|---|---|
| 0 | 0 | I0 |
| 0 | 1 | I1 |
| 1 | 0 | I2 |
| 1 | 1 | I3 |
The AND gates and inverters in the multiplexer simulate a decoder circuit, and certainly, they decode the input selection lines. In common, a 2"-to-1- line multiplexer is produced from an n-to-2" decoder by inserting to it 2" input lines, one from each data input. The size of the multiplexer is determined by the number 2" of its data inputs and the single output. It is then implicit that it also includes n input selection lines.
As in decoders, multiplexers can have an allowed input to control the services of the unit. When the allowed input is in the inactive state, the outputs are disabled, and when it is in the active state, the circuit functions as a normal multiplexer. The allowed input is beneficial for developing two or more multiplexers to a multiplexer with a higher number of inputs.
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