|
|
| (One intermediate revision by one other user not shown) |
| Line 1: |
Line 1: |
| {{About|electronic switching|telecommunications|multiplexing}}
| | My name: Monique Moris<br>My age: 37 years old<br>Country: France<br>Town: Taverny <br>ZIP: 95150<br>Street: 17 Rue Du Faubourg National<br><br>my web-site; home renovations before and after - [http://www.homeimprovementdaily.com Read This method], |
| [[File:Multiplexer2.png|thumb|300px|right|Schematic of a 2-to-1 Multiplexer. It can be equated to a controlled switch.]]
| |
| [[File:Demultiplexer.png|thumb|270px|right|Schematic of a 1-to-2 Demultiplexer. Like a multiplexer, it can be equated to a controlled switch.]]
| |
| In [[electronics]], a '''multiplexer''' (or '''mux''') is a device that selects one of several [[Analog signal|analog]] or [[Digital signal|digital]] input signals and forwards the selected input into a single line.<ref name="Network+ Guide to Networks">{{cite book | last = Dean | first = Tamara | title = Network+ Guide to Networks | publisher = Delmar | year = 2010 | location = | pages = 82–85 | url = http://books.google.com/books?id=UD0h_GqgbHgC&printsec=frontcover&dq=network%2B+guide+to+networks&src=bmrr#v=onepage&q&f=false}}</ref> A multiplexer of 2<sup>''n''</sup> inputs has ''n'' select lines, which are used to select which input line to send to the output.<ref>{{cite book | last = Debashis | first = De | title = Basic Electronics | publisher = Dorling Kindersley | year = 2010 | location = | pages = 557 | url = http://books.google.com/books?id=mT_j4F1bJx4C&printsec=frontcover&dq=Basic+Electronics+By+De+Debashis#v=onepage&q&f=false}}</ref> Multiplexers are mainly used to increase the amount of data that can be sent over the [[Computer network|network]] within a certain amount of time and [[Bandwidth (signal processing)|bandwidth]].<ref name="Network+ Guide to Networks"/> A multiplexer is also called a '''data selector'''.
| |
| | |
| An electronic multiplexer makes it possible for several signals to share one device or resource, for example one [[A/D converter]] or one communication line, instead of having one device per input signal.
| |
| | |
| Conversely, a '''demultiplexer''' (or '''demux''') is a device taking a single input signal and selecting one of many data-output-lines, which is connected to the single input. A multiplexer is often used with a complementary demultiplexer on the receiving end.<ref name="Network+ Guide to Networks"/>
| |
| | |
| An electronic multiplexer can be considered as a [[MISO#Characterization_of_systems|multiple-input, single-output]] switch, and a demultiplexer as a [[MISO#Characterization_of_systems|single-input, multiple-output]] switch.<ref>{{cite book | last = Lipták | first = Béla | title = Instrument engineers' handbook: Process software and digital networks | publisher = CRC Press | year = 2002 | location = | pages = 343 | url = http://books.google.com/books?id=KPjLAyA7HgoC&printsec=frontcover&dq=instrument+engineers'+handbook:+Process+software+and+digital+networks+By+B%C3%A9la+G.+Lipt%C3%A1k#v=onepage&q&f=false}}</ref> The schematic symbol for a multiplexer is an [[isosceles trapezoid]] with the longer parallel side containing the input pins and the short parallel side containing the output pin.<ref>{{cite book | last = Harris | first = David | title = Digital Design and Computer Architecture | publisher = Penrose | year = 2007 | location = | pages = 79 | url = http://books.google.com/books?id=5X7JV5-n0FIC&printsec=frontcover&dq=Digital+design+and+computer+architecture+By+David+Money+Harris,+Sarah+L.+Harris#v=onepage&q&f=false}}</ref> The schematic on the right shows a 2-to-1 multiplexer on the left and an equivalent switch on the right. The <math>sel</math> wire connects the desired input to the output.
| |
| | |
| ==Telecommunications==
| |
| {{Main|Multiplexing}}
| |
| In [[telecommunications]], a multiplexer is a device that combines several input information signals into one output signal, which carries several [[communication channel]]s, by means of some [[multiplexing|multiplex technique]]. A '''demultiplexer''' is, in this context, a device taking a single input signal that carries many channels and separates those over multiple output signals.
| |
| {{Multiplex techniques}}
| |
| | |
| In telecommunications and [[signal processing]], an analog [[time division multiplexing|time division multiplexer]] (TDM) may take several samples of separate analogue signals and combine them into one wide-band analog signal. Alternatively, a digital TDM may combine a limited number of constant [[bit rate]] digital [[data stream]]s into one data stream of a higher data rate, by forming [[Frame (networking)|data frames]] consisting of one timeslot per channel.
| |
| | |
| In telecommunications, [[computer networks]] and [[digital video]], a [[statistical multiplexer]] may combine several variable bit rate data streams into one constant bandwidth signal, for example by means of [[packet mode]] communication. An [[inverse multiplexer]] may utilize several communication channels for transferring one signal.Multipliexer has many inputs and limited outputs on the other hand demultipliexer has many outputs and limited inputs.
| |
| | |
| ==Cost saving==
| |
| [[File:Telephony multiplexer system.gif|thumb|right|300px|The basic function of a multiplexer: combining multiple inputs into a single data stream. On the receiving side, a demultiplexer splits the single data stream into the original multiple signals.]]
| |
| | |
| One use for multiplexers is cost saving by connecting a multiplexer and a '''demultiplexer''' (or '''demux''') together over a single channel (by connecting the multiplexer's single output to the demultiplexer's single input).
| |
| The image to the right demonstrates this.
| |
| In this case, the cost of implementing separate channels for each data source is higher than the cost and inconvenience of providing the multiplexing/demultiplexing functions.
| |
| | |
| At the receiving end of the [[data link]] a complementary ''demultiplexer'' is normally required to break single data stream back down into the original streams.
| |
| In some cases, the far end system may have more functionality than a simple demultiplexer and so, while the demultiplexing still exists logically, it may never actually happen physically.
| |
| This would be typical where a multiplexer serves a number of [[Internet Protocol|IP]] network users and then feeds directly into a [[router (computing)|router]] which immediately reads the content of the entire link into its [[routing]] processor and then does the demultiplexing in memory from where it will be converted directly into IP sections.
| |
| | |
| Often, a multiplexer and demultiplexer are combined together into a single piece of equipment, which is usually referred to simply as a "multiplexer". Both pieces of equipment are needed at both ends of a transmission link because most communications systems transmit in [[Duplex (telecommunications)|both directions]].
| |
| | |
| In [[analog circuit]] design, a multiplexer is a special type of analog switch that connects one signal selected from several inputs to a single output.
| |
| | |
| ==Digital multiplexers==
| |
| In [[digital circuit]] design, the selector wires are of digital value. In the case of a 2-to-1 multiplexer, a logic value of 0 would connect <math>\scriptstyle I_0</math> to the output while a logic value of 1 would connect <math>\scriptstyle I_1</math> to the output.
| |
| In larger multiplexers, the number of selector pins is equal to <math>\scriptstyle \left \lceil \log_2(n) \right \rceil</math> where <math>\scriptstyle n</math> is the number of inputs.
| |
| | |
| For example, 9 to 16 inputs would require no fewer than 4 selector pins and 17 to 32 inputs would require no fewer than 5 selector pins.
| |
| The binary value expressed on these selector pins determines the selected input pin.
| |
| | |
| A 2-to-1 multiplexer has a [[boolean equation]] where <math>\scriptstyle A</math> and <math>\scriptstyle B</math> are the two inputs, <math>\scriptstyle S</math> is the selector input, and <math>\scriptstyle Z</math> is the output:
| |
| : <math>Z = ( A \cdot \overline{S}) + (B \cdot S)</math>
| |
| | |
| [[File:Multiplexer 2-to-1.svg|thumb|350px|A 2-to-1 mux]]
| |
| Which can be expressed as a [[truth table]]:
| |
| {| class="wikitable"
| |
| |-
| |
| |<math>\scriptstyle S</math> || <math>\scriptstyle A</math> || <math>\scriptstyle B</math> || <math>\scriptstyle Z</math>
| |
| |-
| |
| |rowspan="4"| 0
| |
| |rowspan="2"|1 || 1 || 1
| |
| |-
| |
| || 0 || 1
| |
| |-
| |
| |rowspan="2"|0 || 1 || 0
| |
| |-
| |
| || 0 || 0
| |
| |-
| |
| |rowspan="4"| 1
| |
| |rowspan="2"|1 || 1 || 1
| |
| |-
| |
| || 0 || 0
| |
| |-
| |
| |rowspan="2"|0 || 1 || 1
| |
| |-
| |
| || 0 || 0
| |
| |}
| |
| | |
| This truth table shows that when <math>\scriptstyle S=0</math> then <math>\scriptstyle Z=A</math> but when <math>\scriptstyle S=1</math> then <math>\scriptstyle Z=B</math>. A straightforward realization of this 2-to-1 multiplexer would need 2 AND gates, an OR gate, and a NOT gate.
| |
| | |
| Larger multiplexers are also common and, as stated above, require <math>\scriptstyle \left \lceil \log_2(n) \right \rceil</math> selector pins for <math>n</math> inputs. Other common sizes are 4-to-1, 8-to-1, and 16-to-1. Since digital logic uses binary values, powers of 2 are used (4, 8, 16) to maximally control a number of inputs for the given number of selector inputs.
| |
| | |
| <gallery>
| |
| File:Multiplexer 4-to-1.svg|4-to-1 mux
| |
| File:Multiplexer 8-to-1.svg|8-to-1 mux
| |
| File:Multiplexer 16-to-1.svg|16-to-1 mux
| |
| </gallery>
| |
| | |
| The boolean equation for a 4-to-1 multiplexer is:
| |
| :<math>F = (A \cdot \overline{S_0} \cdot \overline{S_1}) + (B \cdot S_0 \cdot \overline {S_1}) + (C \cdot \overline{S_0} \cdot S_1 ) + (D \cdot S_0 \cdot S_1)</math>
| |
| | |
| The following 4-to-1 multiplexer is realized from [[3-state buffers]] and AND gates (the AND gates are acting as the decoder):
| |
| | |
| [[File:Mux from 3 state buffers.png|200px]]
| |
| | |
| Note that the subscripts on the <math>\scriptstyle I_n</math> inputs indicate the decimal value of the binary control inputs at which that input is let through.
| |
| | |
| ===Chaining multiplexers===
| |
| Larger multiplexers can be constructed by using smaller multiplexers by chaining them together. For example, an 8-to-1 multiplexer can be made with two 4-to-1 and one 2-to-1 multiplexers. The two 4-to-1 multiplexer outputs are fed into the 2-to-1 with the selector pins on the 4-to-1's put in parallel giving a total number of selector inputs to 3, which is equivalent to an 8-to-1.
| |
| | |
| ===List of ICs which provide multiplexing===
| |
| The [[7400 series]] has several ICs that contain multiplexer(s):
| |
| {| class="wikitable"
| |
| |-
| |
| ! S.No. !! IC No. !! Function !! Output State
| |
| |-
| |
| | 1
| |
| | 74157
| |
| | Quad 2:1 mux.
| |
| | Output same as input given
| |
| |-
| |
| | 2
| |
| | 74158
| |
| | Quad 2:1 mux.
| |
| | Output is inverted input
| |
| |-
| |
| | 0
| |
| | 74153
| |
| | Dual 4:1 mux.
| |
| | Output same as input
| |
| |-
| |
| | 5
| |
| | 74352
| |
| | Dual 4:1 mux.
| |
| | Output is inverted input
| |
| |-
| |
| | 9
| |
| | 74151A
| |
| | 16:1 mux.
| |
| | Both outputs available (i.e., complementary outputs)
| |
| |-
| |
| | 6
| |
| | 74151
| |
| | 8:1 mux.
| |
| | Output is inverted input
| |
| |-
| |
| | 7
| |
| | 74150
| |
| | 16:1 mux.
| |
| | Output is inverted input
| |
| |}
| |
| | |
| ==Digital demultiplexers==
| |
| Demultiplexers take one data input and a number of selection inputs, and they have several outputs.
| |
| They forward the data input to one of the outputs depending on the values of the selection inputs.
| |
| Demultiplexers are sometimes convenient for designing general purpose logic, because if the demultiplexer's input is always true, the demultiplexer acts as a [[decoder]].
| |
| This means that any function of the selection bits can be constructed by logically OR-ing the correct set of outputs.
| |
| | |
| If X is the input and S is the selector, and A and B are the outputs:
| |
| | |
| <math>A = ( X \cdot \overline{S})</math>
| |
| | |
| <math>B = ( X \cdot S)</math>
| |
| | |
| [[File:Demultiplexer Example01.svg|thumb|450px|left|Example: A Single Bit 1-to-4 Line Demultiplexer]]
| |
| <br clear="all" />
| |
| | |
| ===List of ICs which provide demultiplexing===
| |
| The [[7400 series]] has several ICs that contain demultiplexer(s):
| |
| {| class="wikitable"
| |
| |-
| |
| ! S.No. !! IC No. (7400) !! IC No. (4000) !! Function !! Output State
| |
| |-
| |
| | 1
| |
| | 74139
| |
| |
| |
| | Dual 1:4 demux.
| |
| | Output is inverted input
| |
| |-
| |
| | 3
| |
| | 74156
| |
| |
| |
| | Dual 1:4 demux.
| |
| | Output is [[open collector]]
| |
| |-
| |
| | 4
| |
| | 74138
| |
| |
| |
| | 1:8 demux.
| |
| | Output is inverted input
| |
| |-
| |
| | 5
| |
| | 74238
| |
| |
| |
| | 1:8 demux.
| |
| | |
| |-
| |
| | 6
| |
| | 74154
| |
| |
| |
| | 1:16 demux.
| |
| | Output is inverted input
| |
| |-
| |
| | 7
| |
| | 74159
| |
| | CD4514/15
| |
| | 1:16 demux.
| |
| | Output is open collector and same as input
| |
| |}
| |
| | |
| ==Multiplexers as PLDs==
| |
| Multiplexers can also be used as components of [[programmable logic device]]s. By specifying the logic arrangement in the input signals, a custom logic circuit can be created. The selector inputs then act as the logic inputs. This is especially useful in situations when cost is a factor and for modularity.
| |
| | |
| ==See also==
| |
| {{Wiktionary|multiplexer|demultiplexer}}
| |
| * [[Priority encoder]]
| |
| * [[Inverse multiplexer]]
| |
| * [[Statistical multiplexer]]
| |
| * [[Digital subscriber line access multiplexer]] (DSLAM)
| |
| * [[Rule 184]], a [[cellular automaton]] in which each cell acts as a multiplexer for the values from the two adjacent cells
| |
| * [[Multiplexing]]
| |
| ** [[CDMA|Code-division multiplexing]]
| |
| ** [[Frequency-division multiplexing]]
| |
| ** [[Time-division multiplexing]]
| |
| **[[Wavelength-division multiplexing]]
| |
| **[[Statistical multiplexing]]
| |
| | |
| ==References==
| |
| {{Reflist}}
| |
| | |
| ==Further reading==
| |
| *{{cite book
| |
| |author1=M. Morris Mano
| |
| |author2=Charles R. Kime
| |
| |title=Logic and Computer Design Fundamentals
| |
| |edition=4
| |
| |isbn=0-13-198926-X
| |
| |publisher=[[Prentice Hall]]
| |
| |year=2008
| |
| }}
| |
| | |
| {{commons category|Multiplexers}}
| |
| {{CPU technologies}}
| |
| | |
| [[Category:Multiplexing]]
| |
| [[Category:Digital circuits]]
| |