A Multiplexer (MUX) is a device that can receive multiple input signals and synthesize a single output signal in a recoverable manner for each input signal. It is also an integrated system that usually contains a certain number of data inputs and a single output. Here, as a beginner, what multiplexer really is in CPU?
1 Multiplexer Definition
The very first thing of knowing Multiplexer is clearly understanding its definition by simple description. Multiplexer means many into one. In electronics, a multiplexer (MUX) is a logic gates circuit that employed to fetch a bit of data from computer memory at a given address. What’s more, a computer processor has several multiplexers to control the data and address buses.
In other words, it is a special circuit device that selects one of n inputs and provides it on output. That is, a mutliplexer (Mux) is a device used to select a single output line. In computer architecture, a input comes from multiple input lines using control signals.
2 Reference Note
Multiplexer technology may follow one of the following principles, such as: TDM, FDM, CDM or WDM. For example, Multipexing TDM is a trick. It uses a single link (e.g. pair of wires or radio link) for more than one thing. That’s the Multi bit of multiplexing. It is also common in software operations, such as: simultaneous transmission of multi-threaded information streams to equipment or programs.
The multiplexer follows the following principles. Remember not all have to be obeyed.
Time division Multiplexing:
you allocate timeslots to the individual things you want to send, then send them in turn. There is some sort of synchronising mechansim to let you decode them at the other end.
Frequency division multiplexing
You send each thing as a separate tone on a broad band link, and filter them out separately at the other end.
Phase division multiplexing
Similar to FDM but with some sort of carrier and deteciton of phase distortion of it.
Amplitude division multiplexing
You make a series of logritnmically related levels, and sum them 1V, 2V, 4V. If you recieve 7V you know that all 3 input bits were high.
Circuit division multiplexing (very old fashioned)
Use the same link for different things at different times of day or week. When I world on merchant ships in the 1960s, sending morse code might use a single HF frequency, or for telephony, or for faxing weather maps or “wire image” pictures, at different times during the hour.
3 What is Multiplexer with Example?
1) A Concept
As a beginner, study the multiplexers is not easy. You’ll have questions like this what they do in a CPU or ALU? Here give you an proper description about Multiplexers.
Using a multiplexer is to make full use of the capacity of the communication channel. And you can greatly reduce the cost of the system.
2) An Example
Giving a really simple example:
Like fetch a data bit from computer memory. A multiplexer allows you to specify an address (the input code). And the memory bit will connecte to the other pin.
You have 256 bits of memory, and want to connect this to an output pin. In addition, the multiplexer has 8 bits for input codes. You proved a code say n, which is connected through the logic gates to the output of the multiplexer. This multiplexer would have a total of 256 + 8 input lines.
That is, when the data stream on the multiplexed line is continuous, this sharing method can achieve good results. Obviously, this is more economical than using a communication line for each terminal. Multiplexers are always in pairs during operation. One continuous terminal, the other near the host. Its function is to separate the received composite data stream according to the channel. Finally send them to the corresponding output line. That is a Multiplexer.
The major purpose of a mux shows a construct where selecting lines pick one out of many input signals. In a word, Multiplexer is a selection device.
4 Multiplexer Question
A big question covered in as to where this may be useful? Generally, multiplexers appear everywhere in computer architecture and ASIC design to help pick between multiple signals. In your computer processor, predicting a branch uses multiplexers( when running a loop. Branch is the assembly instruction and the processor needs to guess. Whether it should take the branch or not to get data from caches. Given an index in the cache muxes should pick the correct data out of many. Then select control signals for the processor according to the instruction that comes in. Finally select one out of the many ALU calculations. It is based on the operation needed, and more.
5 Multiplexer Applications
Various applications use a multiplexer wherein multiple data can be transmitted using a single line.
1) Communication System
In communication systems, a multiplexer has a transmission system and also a communication network. It is used to increase the efficiency of the communication system by allowing the transmission of data, such as audio & video data from different channels via cables and single lines.
2) Computer Memory
In computer memory, multiplexer keeps up a vast amount of memory in the computers, and also to decrease the number of copper lines necessary to connect the memory to other parts of the computer.
3) Telephone Network
In telephone networks, a multiplexer integrates the multiple audio signals on a single line of transmission.
4) Transmission from the Computer System of a Satellite
A Multiplexer transmits the data signals from the computer system. It is from a satellite to the ground system by using a GSM communication.
The purpose of using a multiplexer is to make full use of the capacity of the communication channel and greatly reduce the system cost. For example, for a pair of telephone lines, its communication frequency band is generally above 100kHz, and the frequency band of each telephone signal is generally limited to below 4kHz. At this time, the capacity of the channel is far greater than the information transmission volume of a phone.
Using multiplexers, multiple channels of data information can share one channel. When the data stream on the multiplexed line is continuous, this sharing method can achieve good results. Obviously, this is more economical.
Multiplexers are always used in pairs. One continuous terminal, the other near the host. In short, multiplexer plays an important role that help put together a processor, without it, you would have nothing.
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