Data Selectors & Multiplexers | Analog and Digital Electronics - Electrical Engineering (EE) PDF Download

Data Selectors & Multiplexers

Simple way to connect multiple sources of information in analogue electronic systems is by using mechanical switches, such as those illustrated in Fig. 4.2.1. In example (a) a single pole double throw switch is used to select either input A or input B to be connected to output X. Example (b) shows a rotary selector switch that can multiplex any one of eight inputs to a single output.

In digital electronics, selecting multiple data sources can be performed by combinational logic circuits. Logic signals applied to one or more data select inputs initiate the selection of data, which may be steady logic levels or whole streams of digital information. Switching digital signals in this way is much faster and more reliable than using mechanical switch contacts. Digital data selectors and multiplexers are therefore a vital part of many digital systems. The names ‘data selector’ and ‘multiplexer’ are commonly interchanged, with multiplexers called data selectors and vice versa. If there is any difference, a circuit selecting between two inputs may be called a data selector, and more complex circuits combining multiple inputs into a single output, using various methods and existing in both digital and analogue forms, would be called multiplexers.

 

   Data Selectors & Multiplexers | Analog and Digital Electronics - Electrical Engineering (EE)

 

Basic Data Select (Multiplexer) Circuits

A simple data selector consisting of a single XOR gate was used in the 8 Bit Adder/Subtractor circuit shown in Figs. 4.1.5 and 4.1.6 in Module 4.1 to change the function of the circuit from addition to subtraction, but this was only required to select data B or its inverse B. The circuit shown in Fig. 4.2.2 however can select either of two completely independent data inputs.

The operation of Fig. 4.2.2 is quite straightforward and relies on ‘enabling’ either of a pair of NAND gates (1 and 2), but not both.

                Data Selectors & Multiplexers | Analog and Digital Electronics - Electrical Engineering (EE)

 

From the truth table for a NAND gate shown in Table 4.2.1 it can be seen that if one of the inputs (e.g. input A) is kept at logic 1, then the output will be the inverse of the other input. The gate is said to be enabled. If however input A is kept at logic 0, then the output will always be logic 1 whatever the state of the second input. The gate is therefore disabled, and the input cannot reach the output, even in inverted form. Gate 3 in Fig. 4.2.2 is simply combining the inputs from the other two gates. Table 4.2.2 illustrates the operation of Fig.4.2.2.

 

Data Selectors & Multiplexers | Analog and Digital Electronics - Electrical Engineering (EE)

The document Data Selectors & Multiplexers | Analog and Digital Electronics - Electrical Engineering (EE) is a part of the Electrical Engineering (EE) Course Analog and Digital Electronics.
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FAQs on Data Selectors & Multiplexers - Analog and Digital Electronics - Electrical Engineering (EE)

1. What is a data selector and how does it work?
Ans. A data selector is a digital circuit that selects one of many input data signals and outputs it based on the control inputs. It functions like a switch, allowing only one input to pass through based on the control inputs.
2. What is the purpose of using a multiplexer in data selectors?
Ans. A multiplexer is used in data selectors to select and route multiple input data signals to a single output based on the control inputs. It acts as a data selector with multiple inputs and one output, allowing for efficient data routing and selection.
3. How are data selectors and multiplexers different from each other?
Ans. While both data selectors and multiplexers perform similar functions of selecting and routing data, the main difference lies in their configurations. Data selectors typically have multiple outputs and a single input, while multiplexers have multiple inputs and a single output.
4. Can data selectors and multiplexers be used in combination with other digital circuits?
Ans. Yes, data selectors and multiplexers can be used in combination with other digital circuits to create more complex systems. They are often used in conjunction with logic gates, registers, and memory units to build larger digital systems and processors.
5. What are some common applications of data selectors and multiplexers?
Ans. Data selectors and multiplexers find applications in various digital systems and devices. They are commonly used in communication systems, data multiplexing/demultiplexing, memory addressing, and control unit design in microprocessors.
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