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42-413: 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

84-447: 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

126-439: A phototransistor which converts the light pulses to an electrical signal, an amplifier to increase 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

168-407: 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 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

210-421: 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

252-422: 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

294-514: 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

336-495: 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

378-425: A radio receiver connected to a radio transmitter. The received signal 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

420-513: A repeater, these systems are limited in range by 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

462-469: 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

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504-408: 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 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,

546-480: 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

588-414: 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

630-416: Is a type of telephone repeater used in underwater submarine telecommunications cables . This is used to increase 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

672-524: 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,

714-672: 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

756-427: 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

798-410: 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

840-442: 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

882-526: Is used to extend the range of coverage of a radio signal. The history of radio relay repeaters began in 1898 from 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

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924-586: 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

966-416: 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 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

1008-658: 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

1050-671: 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

1092-400: 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,

1134-509: 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

1176-402: 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

1218-421: The details below. Request from 172.68.168.151 via cp1112 cp1112, Varnish XID 390391335 Upstream caches: cp1112 int Error: 429, Too Many Requests at Fri, 29 Nov 2024 05:51:12 GMT 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

1260-405: 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

1302-437: The invention of electronic amplifiers, mechanically coupled carbon microphones were used as amplifiers in telephone repeaters. After 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

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1344-400: 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

1386-406: 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; 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

1428-432: 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 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

1470-413: 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

1512-482: 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 Too Many Requests If you report this error to the Wikimedia System Administrators, please include

1554-468: 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

1596-449: 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 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

1638-415: 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

1680-516: The use of thinner wires. In the 1950s negative impedance gain devices were more popular, and a transistorized version called 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

1722-551: 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 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

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1764-424: 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

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