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59-413: RS-485 supports inexpensive local networks and multidrop communications links, using the same differential signaling over twisted pair as RS-422 . It is generally accepted that RS-485 can be used with data rates up to 10  Mbit/s or, at lower speeds, distances up to 1,200 m (4,000 ft). As a rule of thumb , the speed in bit/s multiplied by the length in meters should not exceed 10. Thus

118-447: A 50-meter cable should not signal faster than 2 Mbit/s . In contrast to RS-422, which has a driver circuit which cannot be switched off, RS-485 drivers use three-state logic allowing individual transmitters to be deactivated. This allows RS-485 to implement linear bus topologies using only two wires. The equipment located along a set of RS-485 wires are interchangeably called nodes, stations or devices. The recommended arrangement of

177-412: A communication channel , it is progressively degraded due to loss of power. For example, when a telephone call passes through a wire telephone line , some of the power in the electric current which represents the audio signal is dissipated as heat in the resistance of the copper wire. The longer the wire, the more power is lost, and the smaller the amplitude of the signal at the far end. So with

236-445: A hotspot service. Network topology describes the layout of interconnections between devices and network segments. At the data link layer and physical layer , a wide variety of LAN topologies have been used, including ring , bus , mesh and star . Simple LANs generally consist of cabling and one or more switches . A switch can be connected to a router , cable modem , or ADSL modem for Internet access. A LAN can include

295-410: A telephone repeater is an amplifier in a telephone line , an optical repeater is an optoelectronic circuit that amplifies the light beam in an optical fiber cable ; and a radio repeater is a radio receiver and transmitter that retransmits a radio signal. A broadcast relay station is a repeater used in broadcast radio and television . When an information-bearing signal passes through

354-489: A wide area network (WAN). Repeater In telecommunications , a repeater is an electronic device that receives a signal and retransmits it. Repeaters are used to extend transmissions so that the signal can cover longer distances or be received on the other side of an obstruction. Some types of repeaters broadcast an identical signal, but alter its method of transmission, for example, on another frequency or baud rate . There are several different types of repeaters;

413-424: A DC current source to increase the power of the alternating current audio signal on the line. Since the telephone is a duplex (bidirectional) communication system, the wire pair carries two audio signals , one going in each direction. So telephone repeaters have to be bilateral, amplifying the signal in both directions without causing feedback, which complicates their design considerably. Telephone repeaters were

472-561: A Defense Department teleconferencing application. This demonstrated the feasibility of employing TCP/IP LANs to interconnect Worldwide Military Command and Control System (WWMCCS) computers at command centers throughout the United States. However, WWMCCS was superseded by the Global Command and Control System (GCCS) before that could happen. During the same period, Unix workstations were using TCP/IP networking. Although

531-421: A city, or neighboring police departments). They may provide links to the public switched telephone network as well, or satellite network ( BGAN , INMARSAT , MSAT ) as an alternative path from source to the destination. Typically a repeater station listens on one frequency, A, and transmits on a second, B. All mobile stations listen for signals on channel B and transmit on channel A. The difference between

590-504: A limited area such as a residence, school, laboratory, university campus or office building. By contrast, a wide area network (WAN) not only covers a larger geographic distance, but also generally involves leased telecommunication circuits . Ethernet and Wi-Fi are the two most common technologies in use for local area networks. Historical network technologies include ARCNET , Token Ring and AppleTalk . The increasing demand and usage of computers in universities and research labs in

649-422: A linear amplifier, and may include electronic filters to compensate for frequency and phase distortion in the line. The digital repeater is used in channels that transmit data by binary digital signals , in which the data is in the form of pulses with only two possible values, representing the binary digits 1 and 0. A digital repeater amplifies the signal, and it also may retime, resynchronize, and reshape

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708-403: A long enough wire the call will not be audible at the other end. Similarly, the greater the distance between a radio station and a receiver , the weaker the radio signal , and the poorer the reception. A repeater is an electronic device in a communication channel that increases the power of a signal and retransmits it, allowing it to travel further. Since it amplifies the signal, it requires

767-493: A polling/selecting central unit with a multidrop bus with Master/slave (technology) arbitration. The development and proliferation of personal computers using the CP/M operating system in the late 1970s, and later DOS -based systems starting in 1981, meant that many sites grew to dozens or even hundreds of computers. The initial driving force for networking was to share storage and printers , both of which were expensive at

826-522: A positive one, A may be considered the non-inverting signal and B as inverting. The RS-485 standard states (paraphrased): The truth tables of most popular devices, starting with the SN75176, show the output signals inverted. This is in accordance with the A/B naming used by most differential transceiver manufacturers, including: These manufacturers all agree on the meaning of the standard, and their practice

885-495: A predictable level of reliable communication over the designed coverage area. Repeaters can be divided into two types depending on the type of data they handle: This type is used in channels that transmit data in the form of an analog signal in which the voltage or current is proportional to the amplitude of the signal, as in an audio signal. They are also used in trunklines that transmit multiple signals using frequency division multiplexing (FDM). Analog repeaters are composed of

944-519: A simple network operating system LAN Manager and its cousin, IBM's LAN Server . None of these enjoyed any lasting success; Netware dominated the personal computer LAN business from early after its introduction in 1983 until the mid-1990s when Microsoft introduced Windows NT . In 1983, TCP/IP was first shown capable of supporting actual defense department applications on a Defense Communication Agency LAN testbed located at Reston, Virginia. The TCP/IP-based LAN successfully supported Telnet , FTP , and

1003-436: A source of electric power . The term "repeater" originated with telegraphy in the 19th century, and referred to an electromechanical device (a relay ) used to regenerate telegraph signals. Use of the term has continued in telephony and data communications . In computer networking , because repeaters work with the actual physical signal, and do not attempt to interpret the data being transmitted, they operate on

1062-472: A sufficient margin for a reliable data transmission even under severe signal degradation across the cable and connectors. This robustness is the main reason why RS-485 is well suited for long-distance networking in noisy environment. In addition to the A and B connections, an optional, third connection may be present (the TIA standard requires the presence of a common return path between all circuit grounds along

1121-480: A wide range of computer and automation systems. In a computer system, SCSI -2 and SCSI-3 may use this specification to implement the physical layer for data transmission between a controller and a disk drive. RS-485 is used for low-speed data communications in commercial aircraft cabins' vehicle bus . It requires minimal wiring and can share the wiring among several seats, reducing weight. These are used in programmable logic controllers and on factory floors. RS-485

1180-495: A wide variety of other network devices such as firewalls , load balancers , and network intrusion detection . Advanced LANs are characterized by their use of redundant links with switches using the spanning tree protocol to prevent loops, their ability to manage differing traffic types via quality of service (QoS), and their ability to segregate traffic with VLANs . At the higher network layers, protocols such as NetBIOS , IPX/SPX , AppleTalk and others were once common, but

1239-414: A wire line or a radio link. While the repeater station is designed for simultaneous reception and transmission, mobile units need not be equipped with the bulky and costly duplexers, as they only transmit or receive at any time. Mobile units in a repeater system may be provided with a "talkaround" channel that allows direct mobile-to-mobile operation on a single channel. This may be used if out of reach of

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1298-537: Is also used in Digital Command Control (DCC) for model railways . The external interface to the DCC command station is often RS-485 used by hand-held controllers or for controlling the layout in a networked PC environment. 8P8C modular connectors are used in this case. RS-485 does not define a communication protocol ; merely an electrical interface. Although many applications use RS-485 signal levels,

1357-403: Is amplified and retransmitted, often on another frequency, to provide coverage beyond the obstruction. Usage of a duplexer can allow the repeater to use one antenna for both receive and transmit at the same time. Radio repeaters improve communication coverage in systems using frequencies that typically have line-of-sight propagation . Without a repeater, these systems are limited in range by

1416-680: Is differential, it resists electromagnetic interference from motors and welding equipment. In theatre and performance venues, RS-485 networks are used to control lighting and other systems using the DMX512 protocol. RS-485 serves as a physical layer for the AES3 digital audio interconnect. RS-485 is also used in building automation as the simple bus wiring and long cable length is ideal for joining remote devices. It may be used to control video surveillance systems or to interconnect security control panels and devices such as access control card readers. It

1475-427: Is in widespread use. The issue also exists in programmable logic controller applications. Care must be taken when using A/B naming. Alternate nomenclature is often used to avoid confusion surrounding the A/B naming: RS-485 standard conformant drivers provide a differential output of a minimum 1.5 V across a 54-Ω load, whereas standard conformant receivers detect a differential input down to 200 mV. The two values provide

1534-410: Is not necessary or desirable in many cases. RS-485 and RS-422 can interoperate with certain restrictions. Converters between RS-485 and RS-232 are available to allow a personal computer to communicate with remote devices. By using repeaters very large RS-485 networks can be formed. TSB-89A, Application Guidelines for TIA/EIA-485-A does not recommend using star topology. RS-485 signals are used in

1593-540: Is still the basis of most commercial LANs today. While optical fiber cable is common for links between network switches , use of fiber to the desktop is rare. In a wireless LAN , users have unrestricted movement within the coverage area. Wireless networks have become popular in residences and small businesses, because of their ease of installation. Most wireless LANs use Wi-Fi as wireless adapters are typically integrated into smartphones , tablet computers and laptops . Guests are often offered Internet access via

1652-442: Is used as the physical layer underlying many standard and proprietary automation protocols used to implement industrial control systems , including the most common versions of Modbus and Profibus . DH 485 is a proprietary communications protocol used by Allen-Bradley in their line of industrial control units. Utilizing a series of dedicated interface devices, it allows PCs and industrial controllers to communicate. Since it

1711-589: Is wise to add some current limiting to the SC connection. Grounds between buildings may vary by a small voltage, but with very low impedance and hence the possibility of catastrophic currents – enough to melt signal cables, PCB traces, and transceiver devices. RS-485 does not specify any connector or pinout. Circuits may be terminated on screw terminals , D-subminiature connectors, or other types of connectors. The standard does not discuss cable shielding but makes some recommendations on preferred methods of interconnecting

1770-463: The Acorn Atom and Acorn System 2 / 3 / 4 computers in 1981. In the 1980s, several token ring network implementations for LANs were developed. IBM released their own implementation of token ring in 1985, It ran at 4  Mbit/s . IBM claimed that their token ring systems were superior to Ethernet, especially under load, but these claims were debated. IBM's implementation of token ring

1829-459: The Internet protocol suite (TCP/IP) has prevailed as the standard of choice. LANs can maintain connections with other LANs via leased lines, leased services, or across the Internet using virtual private network technologies. Depending on how the connections are established and secured, and the distance involved, such linked LANs may also be classified as a metropolitan area network (MAN) or

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1888-465: The physical layer , the first layer of the OSI model ; a multiport Ethernet repeater is usually called a hub . This is used to increase the range of telephone signals in a telephone line. They are most frequently used in trunklines that carry long distance calls. In an analog telephone line consisting of a pair of wires, it consists of an amplifier circuit made of transistors which use power from

1947-511: The E6 repeater was the final major type used in the Bell System before the low cost of digital transmission made all voiceband repeaters obsolete. Frequency frogging repeaters were commonplace in frequency-division multiplexing systems from the middle to late 20th century. This is a type of telephone repeater used in underwater submarine telecommunications cables . This is used to increase

2006-666: The RS-485 designation. The initial edition of EIA RS-485 was dated April 1983. RS-485 only specifies the electrical characteristics of the generator and the receiver: the physical layer . It does not specify or recommend any communications protocol ; Other standards define the protocols for communication over an RS-485 link. The foreword to the standard references The Telecommunications Systems Bulletin TSB-89 which contains application guidelines, including data signaling rate vs. cable length, stub length, and configurations. Section 4 defines

2065-460: The advent of Novell NetWare which provided even-handed support for dozens of competing card and cable types, and a much more sophisticated operating system than most of its competitors. Of the competitors to NetWare, only Banyan Vines had comparable technical strengths, but Banyan never gained a secure base. 3Com produced 3+Share and Microsoft produced MS-Net . These then formed the basis for collaboration between Microsoft and 3Com to create

2124-671: The balanced line for proper operation) called SC , G or reference , the common signal reference ground used by the receiver to measure the A and B voltages. This connection may be used to limit the common-mode signal that can be impressed on the receiver inputs. The allowable common-mode voltage is in the range −7 V to +12 V, i.e. ±7 V on top of the 0–5 V signal range. Failure to stay within this range will result in, at best, signal corruption, and, at worst, damage to connected devices. Care must be taken that an SC connection, especially over long cable runs, does not result in an attempt to connect disparate grounds together – it

2183-672: The benches of the European Parliament Hemicycles in Strasbourg and Luxembourg. Early Ethernet ( 10BASE-5 and 10BASE-2 ) used coaxial cable . Shielded twisted pair was used in IBM's Token Ring LAN implementation. In 1984, StarLAN showed the potential of simple unshielded twisted pair by using category 3 cable —the same cable used for telephone systems. This led to the development of 10BASE-T (and its twisted-pair successors ) and structured cabling which

2242-400: The cable characteristic impedance (typically, 120 ohms for twisted pairs). The termination also includes pull up and pull down resistors to establish bias for each data wire for the case when the lines are not being driven by any device. This way, the lines will be biased to known voltages and nodes will not interpret the noise from undriven lines as actual data; without biasing resistors,

2301-467: The curvature of the Earth and the blocking effect of terrain or high buildings. A repeater on a hilltop or tall building can allow stations that are out of each other's line-of-sight range to communicate reliably. Radio repeaters may also allow translation from one set of radio frequencies to another, for example to allow two different public service agencies to interoperate (say, police and fire services of

2360-514: The data lines float in such a way that electrical noise sensitivity is greatest when all device stations are silent or unpowered. The EIA once labeled all its standards with the prefix RS ( Recommended Standard ), but the EIA/TIA officially replaced RS with EIA/TIA to help identify the origin of its standards. The EIA has officially disbanded and the standard is now maintained by the TIA as TIA-485, but engineers and applications guides continue to use

2419-402: The data onto all other spans. Ideally, the two ends of the cable will have a termination resistor connected across the two wires. Without termination resistors, signal reflections off the unterminated end of the cable can cause data corruption. Termination resistors also reduce electrical noise sensitivity due to the lower impedance . The value of each termination resistor should be equal to

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2478-405: The electrical characteristics of the generator (transmitter or driver), receiver, transceiver, and system. These characteristics include: definition of a unit load, voltage ranges, open-circuit voltages, thresholds, and transient tolerance. It also defines three generator interface points (signal lines); A, B and C. The data is transmitted on A and B. C is a ground reference. This section also defines

2537-431: The first type of repeater and were some of the first applications of amplification. The development of telephone repeaters between 1900 and 1915 made long-distance phone service possible. Now, most telecommunications cables are fiber-optic cables which use optical repeaters (below). Before the invention of electronic amplifiers, mechanically coupled carbon microphones were used as amplifiers in telephone repeaters. After

2596-503: The late 1960s generated the need to provide high-speed interconnections between computer systems. A 1970 report from the Lawrence Radiation Laboratory detailing the growth of their "Octopus" network gave a good indication of the situation. A number of experimental and early commercial LAN technologies were developed in the 1970s. Ethernet was developed at Xerox PARC between 1973 and 1974. Cambridge Ring

2655-400: The logic states 1 (off) and 0 (on), by the polarity between A and B terminals. If A is negative with respect to B, the state is binary 1. The reversed polarity (A positive with respect to B) is binary 0. The standard does not assign any logic function to the two states. RS-485, like RS-422, can be made full-duplex by using four wires. Since RS-485 is a multi-point specification, however, this

2714-454: The power of the signal, an electronic filter which reshapes the pulses, and a laser which converts the electrical signal to light again and sends it out the other fiber. However, optical amplifiers are being developed for repeaters to amplify the light itself without the need of converting it to an electric signal first. This is used to extend the range of coverage of a radio signal. The history of radio relay repeaters began in 1898 from

2773-493: The publication by Johann Mattausch in Austrian Journal Zeitschrift für Electrotechnik (v. 16, 35 - 36). But his proposal "Translator" was primitive and not suitable for use. The first relay system with radio repeaters, which really functioned, was that invented in 1899 by Emile Guarini-Foresio. A radio repeater usually consists of a radio receiver connected to a radio transmitter. The received signal

2832-401: The range of signals in a fiber-optic cable . Digital information travels through a fiber-optic cable in the form of short pulses of light. The light is made up of particles called photons , which can be absorbed or scattered in the fiber. An optical communications repeater usually consists of a phototransistor which converts the light pulses to an electrical signal, an amplifier to increase

2891-413: The repeater system, or for communications not requiring the attention of all mobiles. The "talkaround" channel may be the repeater output frequency; the repeater will not retransmit any signals on its output frequency. An engineered radio communication system designer will analyze the coverage area desired and select repeater locations, elevations, antennas, operating frequencies and power levels to permit

2950-400: The signal reference common and equipment case grounds. The diagram below shows potentials of the A (blue) and B (red) pins of an RS-485 line before, during, and after transmission of one byte (0xD3, least significant bit first) of data using an asynchronous start-stop method. Local network A local area network ( LAN ) is a computer network that interconnects computers within

3009-472: The speed, format, and protocol of the data transmission are not specified by RS-485. Interoperability of even similar devices from different manufacturers is not assured by compliance with the signal levels alone. The RS-485 differential line consists of two signals: Because a mark (logic 1) condition is traditionally represented (e.g. in RS-232) with a negative voltage; and space (logic 0) represented with

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3068-563: The time. There was much enthusiasm for the concept, and for several years, from about 1983 onward, computer industry pundits habitually declared the coming year to be, "The year of the LAN". In practice, the concept was marred by the proliferation of incompatible physical layer and network protocol implementations, and a plethora of methods of sharing resources. Typically, each vendor would have its own type of network card, cabling, protocol, and network operating system . A solution appeared with

3127-432: The turn of the 20th century it was found that negative resistance mercury lamps could amplify, and they were used. The invention of audion tube repeaters around 1916 made transcontinental telephony practical. In the 1930s vacuum tube repeaters using hybrid coils became commonplace, allowing the use of thinner wires. In the 1950s negative impedance gain devices were more popular, and a transistorized version called

3186-415: The two frequencies may be relatively small compared to the frequency of operation, say 1%. Often the repeater station will use the same antenna for transmission and reception; highly selective filters called "duplexers" separate the faint incoming received signal from the billions of times more powerful outbound transmitted signal. Sometimes separate transmitting and receiving locations are used, connected by

3245-424: The wires is as a connected series of point-to-point (multidropped) nodes, i.e. a line or bus , not a star , ring , or multiply connected network. Star and ring topologies are not recommended because of signal reflections or excessively low or high termination impedance. If a star configuration is unavoidable, special RS-485 repeaters are available which bidirectionally listen for data on each span and then retransmit

3304-530: The workstation market segment is now much reduced, the technologies developed in the area continue to be influential on the Internet and in all forms of networking—and the TCP/IP protocol has replaced IPX , AppleTalk , NBF , and other protocols used by the early PC LANs. Econet was Acorn Computers's low-cost local area network system, intended for use by schools and small businesses. It was first developed for

3363-651: Was a relatively high-speed choice of that era, with speeds such as 100 Mbit/s. By 1994, vendors included Cisco Systems , National Semiconductor , Network Peripherals, SysKonnect (acquired by Marvell Technology Group ), and 3Com . FDDI installations have largely been replaced by Ethernet deployments. In 1979, the Electronic voting systems for the European Parliament was using 10 kilometers of simple unshielded twisted pair category 3 cable —the same cable used for telephone systems—installed inside

3422-530: Was developed at Cambridge University starting in 1974. ARCNET was developed by Datapoint Corporation in 1976 and announced in 1977. It had the first commercial installation in December 1977 at Chase Manhattan Bank in New York. In 1979, the Electronic voting systems for the European Parliament was the first installation of a LAN connecting hundreds (420) of microprocessor-controlled voting terminals to

3481-624: Was the basis of the IEEE 802.5 standard. A 16 Mbit/s version of Token Ring was standardized by the 802.5 working group in 1989. IBM had market dominance over Token Ring, for example, in 1990, IBM equipment was the most widely used for Token Ring networks. Fiber Distributed Data Interface (FDDI), a LAN standard, was considered an attractive campus backbone network technology in the early to mid 1990s since existing Ethernet networks only offered 10 Mbit/s data rates and Token Ring networks only offered 4 Mbit/s or 16 Mbit/s rates. Thus it

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