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79-590: A universal synchronous and asynchronous receiver-transmitter ( USART , programmable communications interface or PCI ) is a type of a serial interface device that can be programmed to communicate asynchronously or synchronously. See universal asynchronous receiver-transmitter (UART) for a discussion of the asynchronous capabilities of these devices. The USART's synchronous capabilities were primarily intended to support synchronous protocols like IBM's synchronous transmit-receive (STR), binary synchronous communications (BSC), synchronous data link control (SDLC), and

158-419: A function generator , using a non-linear resistance card to supply approximations to trigonometric functions. For example, the shaft rotation might represent an angle, and the voltage division ratio can be made proportional to the cosine of the angle. The potentiometer can be used as a voltage divider to obtain a manually adjustable output voltage at the slider (wiper) from a fixed input voltage applied across

237-407: A resistive element , a sliding contact (wiper) that moves along the element, making good electrical contact with one part of it, electrical terminals at each end of the element, a mechanism that moves the wiper from one end to the other, and a housing containing the element and wiper. Many inexpensive potentiometers are constructed with a resistive element (B in cutaway drawing) formed into an arc of

316-487: A 16-byte FIFO , and spawned many variants, including the 16C550, 16C650, 16C750, and 16C850 . Depending on the manufacturer, different terms are used to identify devices that perform the UART functions. Intel called their 8251 device a "Programmable Communication Interface". MOS Technology 6551 was known under the name "Asynchronous Communications Interface Adapter" (ACIA). The term "Serial Communications Interface" (SCI)

395-409: A DOS system requires that interrupts not be disabled for more than 1 millisecond at a time. Some hard disk drives and video controllers violate this specification. 9600 bit/s will deliver a character approximately every millisecond, so a 1-byte FIFO should be sufficient at this rate on a DOS system which meets the maximum interrupt disable timing. Rates above this may receive a new character before

474-409: A ceramic/metal mixture called cermet . Conductive track potentiometers use conductive polymer resistor pastes that contain hard-wearing resins and polymers, solvents, and lubricant, in addition to the carbon that provides the conductive properties. Multiturn potentiometers are also operated by rotating a shaft, but by several turns rather than less than a full turn. Some multiturn potentiometers have

553-503: A circle usually a little less than a full turn and a wiper (C) sliding on this element when rotated, making electrical contact. The resistive element can be flat or angled. Each end of the resistive element is connected to a terminal (E, G) on the case. The wiper is connected to a third terminal (F), usually between the other two. On panel potentiometers, the wiper is usually the center terminal of three. For single-turn potentiometers, this wiper typically travels just under one revolution around

632-490: A circuit. The word rheostat was coined in 1843 by Sir Charles Wheatstone , from the Greek ῥέος rheos meaning "stream", and - στάτης - states (from ἱστάναι histanai , "to set, to cause to stand") meaning "setter, regulating device", which is a two-terminal variable resistor. For low-power applications (less than about 1 watt) a three-terminal potentiometer is often used, with one terminal unconnected or connected to

711-450: A linear resistive element with a sliding contact moved by a lead screw; others have a helical resistive element and a wiper that turns through 10, 20, or more complete revolutions, moving along the helix as it rotates. Multiturn potentiometers, both user-accessible and preset, allow finer adjustments; rotation through the same angle changes the setting by typically a tenth as much as for a simple rotary potentiometer. A string potentiometer

790-436: A logarithmic law. The two resistive tracks overlap at approximately 50% of the potentiometer rotation; this gives a stepwise logarithmic taper. A logarithmic potentiometer can also be simulated with a linear one and an external resistor. True logarithmic potentiometers are significantly more expensive. Logarithmic taper potentiometers are often used for volume or signal level in audio systems, as human perception of audio volume

869-409: A multiple of the data rate, typically 8 or 16 times the bit rate. The receiver tests the state of the incoming signal on each clock pulse, looking for the beginning of the start bit. If the apparent start bit lasts at least one-half of the bit time, it is valid and signals the start of a new character. If not, it is considered a spurious pulse and is ignored. After waiting a further bit time, the state of

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948-400: A multitasking system or if handling interrupts from disk controllers. High-speed modems used UARTs that were compatible with the original chip but which included additional FIFO buffers, giving software additional time to respond to incoming data. A look at the performance requirements at high bit rates shows why the 16-, 32-, 64- or 128-byte FIFO is a necessity. The Microsoft specification for

1027-486: A non-contact potentiometer can be found with the AS5600 integrated circuit. However, absolute encoders must also use similar principles, although being for industrial use, certainly the cost must be unfeasible for use in domestic appliances. The most common way to vary the resistance in a circuit continuously is to use a rheostat . Because of the change in resistance, they can also be used to adjust magnitude of current in

1106-427: A percentage is referenced with a non-linear taper, it relates to the resistance value at the midpoint of the shaft rotation. A 10% log taper would therefore measure 10% of the total resistance at the midpoint of the rotation; i.e. 10% log taper on a 10 kOhm potentiometer would yield 1 kOhm at the midpoint. The higher the percentage, the steeper the log curve. A linear taper potentiometer ( linear describes

1185-416: A potentiometer has a resistance, taper, or, "curve" (or law) of a logarithmic (log) form, is used as the volume control in audio power amplifiers , where it is also called an "audio taper pot", because the amplitude response of the human ear is approximately logarithmic. It ensures that on a volume control marked 0 to 10, for example, a setting of 5 sounds subjectively half as loud as a setting of 10. There

1264-448: A received character. Many UARTs have a small first-in, first-out ( FIFO ) buffer memory between the receiver shift register and the host system interface. This allows the host processor even more time to handle an interrupt from the UART and prevents loss of received data at high rates. Transmission operation is simpler as the timing does not have to be determined from the line state, nor is it bound to any fixed timing intervals. As soon as

1343-463: A small area works well. A disadvantage is that sufficient force must be applied to make contact. Another is that the sensor requires occasional calibration to match touch location to the underlying display. (Capacitive sensors require no calibration or contact force, only proximity of a finger or other conductive object. However, they are significantly more complex.) Potentiometers are rarely used to directly control significant amounts of power (more than

1422-547: A small computer. Gordon Bell of DEC designed the first UART, occupying an entire circuit board called a line unit , for the PDP series of computers beginning with the PDP-1 . According to Bell, the main innovation of the UART was its use of sampling to convert the signal into the digital domain, allowing more reliable timing than previous circuits that used analog timing devices with manually adjusted potentiometers . To reduce

1501-473: A transmit FIFO (first in first out) buffer to allow a CPU or DMA controller to deposit multiple characters in a burst into the FIFO rather than have to deposit one character at a time into the shift register. Since transmission of a single or multiple characters may take a long time relative to CPU speeds, a UART maintains a flag showing busy status so that the host system knows if there is at least one character in

1580-522: A very wide variety of equipment functions. The widespread use of potentiometers in consumer electronics declined in the 1990s, with rotary incremental encoders , up/down push-buttons , and other digital controls now more common. However they remain in many applications, such as volume controls and as position sensors. Low-power potentiometers, both slide and rotary, are used to control audio equipment, changing loudness, frequency attenuation, and other characteristics of audio signals. The 'log pot', that is,

1659-529: A watt or so). Instead they are used to adjust the level of analog signals (for example volume controls audio equipment ), and as control inputs for electronic circuits. For example, a light dimmer uses a potentiometer to control the switching of a TRIAC and so indirectly to control the brightness of lamps. Preset potentiometers are widely used throughout electronics wherever adjustments must be made during manufacturing or servicing. User-actuated potentiometers are widely used as user controls, and may control

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1738-484: Is a multi-turn potentiometer operated by an attached reel of wire turning against a spring, allowing it to convert linear position to a variable resistance. User-accessible rotary potentiometers can be fitted with a switch which operates usually at the anti-clockwise extreme of rotation. Before digital electronics became the norm such a component was used to allow radio and television receivers and other equipment to be switched on at minimum volume with an audible click, then

1817-539: Is a three- terminal resistor with a sliding or rotating contact that forms an adjustable voltage divider . If only two terminals are used, one end and the wiper, it acts as a variable resistor or rheostat . The measuring instrument called a potentiometer is essentially a voltage divider used for measuring electric potential (voltage); the component is an implementation of the same principle, hence its name. Potentiometers are commonly used to control electrical devices such as volume controls on audio equipment. It

1896-457: Is also an anti-log pot or reverse audio taper which is simply the reverse of a logarithmic potentiometer. It is almost always used in a ganged configuration with a logarithmic potentiometer, for instance, in an audio balance control. Potentiometers used in combination with filter networks act as tone controls or equalizers . In audio systems, the word linear, is sometimes applied in a confusing way to describe slide potentiometers because of

1975-465: Is also used in speed control of fans. Potentiometers operated by a mechanism can be used as position transducers , for example, in a joystick . Potentiometers are rarely used to directly control significant power (more than a watt ), since the power dissipated in the potentiometer would be comparable to the power in the controlled load. Some terms in the electronics industry used to describe certain types of potentiometers are: Potentiometers consist of

2054-753: Is an upwardly compatible version of the 2691, featuring selectable 8- or 16-byte transmitter and receiver FIFOs, improved support for extended data rates, and faster bus timing characteristics, making the device more suitable for use with high performance microprocessors. Both the 2691 and 28L91 may also be operated in TIA-422 and TIA-485 modes, and may also be programmed to support non-standard data rates. The devices are produced in PDIP-40, PLCC-44 and 44 pin QFP packages, and are readily adaptable to both Motorola and Intel buses. They have also been successfully adapted to

2133-548: Is designed to follow a logarithmic taper, aka a mathematical exponent or "squared" profile. A logarithmic taper potentiometer is constructed with a resistive element that either "tapers" in from one end to the other, or is made from a material whose resistivity varies from one end to the other. This results in a device where output voltage is a logarithmic function of the slider position. Most (cheaper) "log" potentiometers are not accurately logarithmic, but use two regions of different resistance (but constant resistivity) to approximate

2212-1042: Is large compared to the other resistances (like the input to an operational amplifier ), the output voltage can be approximated by the simpler equation: V L = R 2 R 1 + R 2 ⋅ V s . {\displaystyle V_{\mathrm {L} }={R_{2} \over R_{1}+R_{2}}\cdot V_{s}.} (dividing throughout by R L and cancelling terms with R L as denominator) As an example, assume V S = 10   V {\displaystyle V_{\mathrm {S} }=10\ \mathrm {V} } , R 1 = 1   k Ω {\displaystyle R_{1}=1\ \mathrm {k\Omega } } , R 2 = 2   k Ω {\displaystyle R_{2}=2\ \mathrm {k\Omega } } , and R L = 100   k Ω . {\displaystyle R_{\mathrm {L} }=100\ \mathrm {k\Omega } .} Since

2291-532: Is logarithmic, according to the Weber–Fechner law . Unlike mechanical potentiometers, non-contact potentiometers use an optical disk to trigger an infrared sensor, or a magnet to trigger a magnetic sensor (as long as there are other types of sensors, such as capacitive, other types of non-contact potentiometers can probably be built), and then an electronic circuit does the signal processing to provide an output signal that can be analogue or digital. An example of

2370-510: Is proportional to the fraction of the total device resistance in circuit. Carbon-pile rheostats are used as load banks for testing automobile batteries and power supplies. A digital potentiometer (often called digipot) is an electronic component that mimics the functions of analog potentiometers. Through digital input signals, the resistance between two terminals can be adjusted, just as in an analog potentiometer. There are two main functional types: volatile, which lose their set position if power

2449-433: Is removed, and are usually designed to initialise at the minimum position, and non-volatile, which retain their set position using a storage mechanism similar to flash memory or EEPROM . Usage of a digipot is far more complex than that of a simple mechanical potentiometer, and there are many limitations to observe; nevertheless they are widely used, often for factory adjustment and calibration of equipment, especially where

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2528-456: Is the simplest method of measuring the angle or displacement. Potentiometers are also very widely used as a part of displacement transducers because of the simplicity of construction and because they can give a large output signal. In analog computers , high precision potentiometers are used to scale intermediate results by desired constant factors, or to set initial conditions for a calculation. A motor-driven potentiometer may be used as

2607-400: Is up to 95% and up to 99% with 9000 byte jumbo frames . However due to Ethernet's protocol overhead and minimum payload size of 42 bytes, if small messages of one or a few bytes are to be sent, Ethernet's protocol efficiency drops much lower than the UART's 8N1 constant efficiency of 80%. The idle, no data state is high-voltage, or powered. This is a historic legacy from telegraphy, in which

2686-557: Is used, but the letter code definitions are not standardized. Potentiometers made in Asia and the US are usually marked with an "A" for logarithmic taper or a "B" for linear taper; "C" for the rarely seen reverse logarithmic taper. Others, particularly those from Europe, may be marked with an "A" for linear taper, a "C" or "B" for logarithmic taper, or an "F" for reverse logarithmic taper. The code used also varies between different manufacturers. When

2765-467: The 65C02 and 65C816 buses. The 28L91 will operate on 3.3 or 5 volts. The 2692 has a single-byte transmitter holding register and a 4-byte receiver FIFO for each channel. Maximum standard speed of both of the 2692's channels is 115.2 kbit/s. The 26C92 is an upwardly compatible version of the 2692, with 8-byte transmitter and receiver FIFOs for improved performance during continuous bi-directional asynchronous transmission (CBAT) on both channels at

2844-580: The Data link layer . Some early telegraph schemes used variable-length pulses (as in Morse code ) and rotating clockwork mechanisms to transmit alphabetic characters. The first serial communication devices (with fixed-length pulses) were rotating mechanical switches ( commutators ). Various character codes using 5, 6, 7, or 8 data bits became common in teleprinters and later as computer peripherals. The teletypewriter made an excellent general-purpose I/O device for

2923-594: The IETF standard point-to-point protocol (PPP) in HDLC-like framing as defined in RFC   1662. The operation of a USART is intimately related to the various protocols; refer to those pages for details. This section only provides a few general notes. Universal asynchronous receiver-transmitter It was one of the earliest computer communication devices, used to attach teletypewriters for an operator console . It

3002-404: The "potentiometer" every time the equipment is powered up, a multiplying DAC can be used in place of a digipot, and this can offer higher setting resolution, less drift with temperature, and more operational flexibility. A membrane potentiometer uses a conductive membrane that is deformed by a sliding element to contact a resistor voltage divider. Linearity can range from 0.50% to 5% depending on

3081-493: The 65C02 and 65C816 buses. The 28L92 will operate on 3.3 or 5 volts. Modems for personal computers that plug into a motherboard slot must also include the UART function on the card. The original 8250 UART chip shipped with the IBM personal computer had a one character buffer for the receiver and the transmitter each, which meant that communications software performed poorly at speeds above 9600 bit/s, especially if operating under

3160-641: The CPU timing is critical), the UART chip can thus be omitted, saving money and space. The technique is known as bit-banging . A dual UART, or DUART , combines two UARTs into a single chip. Similarly, a quadruple UART or QUART , combines four UARTs into one package, such as the NXP 28L194. An octal UART or OCTART combines eight UARTs into one package, such as the Exar XR16L788 or the NXP SCC2698. The 28L91

3239-620: The ISO-standard high-level data link control (HDLC) synchronous link-layer protocols, which were used with synchronous voice-frequency modems . These protocols were designed to make the best use of bandwidth when modems were analog devices. In those times, the fastest asynchronous voice-band modem could achieve at most speeds of 300   bit/s using frequency-shift keying (FSK) modulation, while synchronous modems could run at speeds up to 9600   bit/s using phase-shift keying (PSK). Synchronous transmission used only slightly over 80% of

Universal synchronous and asynchronous receiver-transmitter - Misplaced Pages Continue

3318-584: The bandwidth of the now more-familiar asynchronous transmission, since start and stop bits were unnecessary. Those modems are obsolete, having been replaced by modems which convert asynchronous data to synchronous forms, but similar synchronous telecommunications protocols survive in numerous block-oriented technologies such as the widely used IEEE 802.2 (Ethernet) link-level protocol. USARTs are still sometimes integrated with MCUs. USARTs are still used in routers that connect to external CSU/DSU devices, and they often use either Cisco's proprietary HDLC implementation or

3397-412: The centering of the display on an analog cathode-ray oscilloscope . Precision potentiometers have an accurate relationship between resistance and slider position. A logarithmic taper potentiometer is a potentiometer that has a bias built into the resistive element. Basically this means the center position of the potentiometer is not one half of the total value of the potentiometer. The resistive element

3476-428: The contact. The only point of ingress for contamination is the narrow space between the shaft and the housing it rotates in. Another type is the linear slider potentiometer, which has a wiper which slides along a linear element instead of rotating. Contamination can potentially enter anywhere along the slot the slider moves in, making effective sealing more difficult and compromising long-term reliability. An advantage of

3555-494: The cost of wiring, backplane and other components, these computers also pioneered flow control using XON and XOFF characters rather than hardware wires. DEC condensed the line unit design into an early single-chip UART for their own use. Western Digital developed this into the first widely available single-chip UART, the WD1402A, around 1971. This was an early example of a medium-scale integrated circuit . Another popular chip

3634-476: The electrical characteristic of the device, not the geometry of the resistive element) has a resistive element of constant cross-section, resulting in a device where the resistance between the contact (wiper) and one end terminal is proportional to the distance between them. Linear taper potentiometers are used when the division ratio of the potentiometer must be proportional to the angle of shaft rotation (or slider position), for example, controls used for adjusting

3713-412: The external signals used between different items of equipment. Separate interface devices are used to convert the logic level signals of the UART to and from the external signaling levels, which may be standardized voltage levels, current levels, or other signals. Communication may be 3 modes: For UART to work the following settings need to be the same on both the transmitting and receiving side: For

3792-405: The falling edge of the start bit only, and then read the center of each expected data bit, and this system works if the broadcast data rate is accurate enough to allow the stop bits to be sampled reliably. It is a standard feature for a UART to store the most recent character while receiving the next. This "double buffering" gives a receiving computer an entire character transmission time to fetch

3871-456: The genericized brand name "trimpot". The relationship between slider position and resistance, known as the "taper" or "law", can be controlled during manufacture by changing the composition or thickness of the resistance coating along the resistance element. Although in principle any taper is possible, two types are widely manufactured: linear and logarithmic (aka "audio taper") potentiometers. A letter code may be used to identify which taper

3950-628: The hardware cables and a chip to do the USB and UART conversion. Cypress Semiconductor and FTDI are two of the significant commercial suppliers of these chips. Although RS-232 ports are no longer available to users on the outside of most computers, many internal processors have UARTs built into their chips to give hardware designers the ability to interface with other chips or devices that use RS-232 or RS-485 for communication. A UART contains those following components: The universal asynchronous receiver-transmitter (UART) takes bytes of data and transmits

4029-469: The host processor transfers the received data. Communicating UARTs have no shared timing system apart from the communication signal. Typically, UARTs resynchronize their internal clocks on each change of the data line that is not considered a spurious pulse. Obtaining timing information in this manner, they reliably receive when the transmitter is sending at a slightly different speed than it should. Simplistic UARTs do not do this; instead they resynchronize on

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4108-508: The host system. Typical serial ports used with personal computers connected to modems use eight data bits, no parity, and one stop bit; for this configuration, the number of ASCII characters per second equals the bit rate divided by 10. Some very low-cost home computers or embedded systems that lack a physical UART may instead emulate the protocol with software by sampling the state of an input port or directly manipulating an output port for data transmission. While very CPU-intensive (since

4187-453: The individual bits in a sequential fashion. At the destination, a second UART re-assembles the bits into complete bytes. Each UART contains a shift register , which is the fundamental method of conversion between serial and parallel forms. Serial transmission of digital information (bits) through a single wire or other medium is less costly than parallel transmission through multiple wires. The UART usually does not directly generate or receive

4266-431: The knob. Other potentiometers are enclosed within the equipment and are intended to only be adjusted when calibrating the equipment during manufacture or repair, and not otherwise touched. They are usually physically much smaller than user-accessible potentiometers, and may need to be operated by a screwdriver rather than having a knob. They are usually called "trimmer", "trim[ming]", or "preset" potentiometers (or pots), or

4345-488: The limitations of mechanical potentiometers are problematic. A digipot is generally immune to the effects of moderate long-term mechanical vibration or environmental contamination, to the same extent as other semiconductor devices, and can be secured electronically against unauthorised tampering by protecting the access to its programming inputs by various means. In equipment which has a microprocessor , FPGA or other functional logic which can store settings and reload them to

4424-407: The line is again sampled and the resulting level clocked into a shift register. After the required number of bit periods for the character length (5 to 8 bits, typically) have elapsed, the contents of the shift register are made available (in parallel fashion) to the receiving system. The UART will set a flag indicating new data is available, and may also generate a processor interrupt to request that

4503-515: The line is held high to show that the line and transmitter are not damaged. Each character is framed as a logic low start bit, data bits, possibly a parity bit and one or more stop bits. In most applications the least significant data bit (the one on the left in this diagram) is transmitted first, but there are exceptions (such as the IBM 2741 printing terminal). All operations of the UART hardware are controlled by an internal clock signal which runs at

4582-605: The load resistance is large compared to the other resistances, the output voltage V L will be approximately: 2   k Ω 1   k Ω + 2   k Ω ⋅ 10   V = 2 3 ⋅ 10   V ≈ 6.667   V . {\displaystyle {2\ \mathrm {k\Omega } \over 1\ \mathrm {k\Omega } +2\ \mathrm {k\Omega } }\cdot 10\ \mathrm {V} ={2 \over 3}\cdot 10\ \mathrm {V} \approx 6.667\ \mathrm {V} .} Because of

4661-417: The load resistance, however, it will actually be slightly lower: ≈ 6.623 V . One of the advantages of the potential divider compared to a variable resistor in series with the source is that, while variable resistors have a maximum resistance where some current will always flow, dividers are able to vary the output voltage from maximum ( V S ) to ground (zero volts) as the wiper moves from one end of

4740-662: The material, design and manufacturing process. The repeat accuracy is typically between 0.1 mm and 1.0 mm with a theoretically infinite resolution. The service life of these types of potentiometers is typically 1 million to 20 million cycles depending on the materials used during manufacturing and the actuation method; contact and contactless (magnetic) methods are available (to sense position). Many different material variations are available such as PET , FR4, and Kapton. Membrane potentiometer manufacturers offer linear, rotary, and application-specific variations. The linear versions can range from 9 mm to 1000 mm in length and

4819-596: The maximum rate to over 300,000 bit/s. A second benefit to having a FIFO is that the computer only has to service about 8 to 12% as many interrupts, allowing more CPU time for updating the screen, or doing other chores. Thus the computer's responses will improve as well. Since the UART's communication protocol is simple, it can be emulated by bit banging GPIO pins in software on modern microcontrollers (e.g. Arduino or Teensy ), or on programmable I/O state machines (e.g. Raspberry Pi Pico 's PIO or NXP 's FlexIO ). Potentiometer A potentiometer

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4898-823: The maximum standard speed of 230.4 kbit/s. The letter C in the 26C92 part number has nothing to do with the fabrication process; all NXP UARTs are CMOS devices. The 28L92 is an upwardly compatible version of the 26C92, featuring selectable 8- or 16-byte transmitter and receiver FIFOs, improved support for extended data rates, and faster bus timing characteristics, making the device more suitable for use with high performance microprocessors. The 2692, 26C92 and 28L92 may be operated in TIA-422 and TIA-485 modes, and may also be programmed to support non-standard data rates. The devices are produced in PDIP-40, PLCC-44 and 44 pin QFP packages, and are readily adaptable to both Motorola and Intel buses. They have also been successfully adapted to

4977-437: The old one has been fetched, and thus the old character will be lost. This is referred to as an overrun error and results in one or more lost characters. A 16-byte FIFO allows up to 16 characters to be received before the computer has to service the interrupt. This increases the maximum bit rate the computer can process reliably from 9600 to 153,000 bit/s if it has a 1 millisecond interrupt dead time. A 32-byte FIFO increases

5056-406: The other two, formerly unconnected, provides the other coordinate. Alternating rapidly between pairs of edges provides frequent position updates. An analog-to-digital converter provides output data. Advantages of such sensors are that only five connections to the sensor are needed, and the associated electronics is comparatively simple. Another is that any material that depresses the top layer over

5135-428: The rotary versions range from 20 to 450 mm in diameter, with each having a height of 0.5 mm. Membrane potentiometers can be used for position sensing. For touch-screen devices using resistive technology, a two-dimensional membrane potentiometer provides x and y coordinates. The top layer is thin glass spaced close to a neighboring inner layer. The underside of the top layer has a transparent conductive coating;

5214-475: The sending system deposits a character in the shift register (after completion of the previous character), the UART generates a start bit, shifts the required number of data bits out to the line, generates and sends the parity bit (if used), and sends the stop bits. Since full-duplex operation requires characters to be sent and received at the same time, UARTs use two different shift registers for transmitted and received characters. High performance UARTs could contain

5293-478: The slider potentiometer is that the slider position gives a visual indication of its setting. While the setting of a rotary potentiometer can be seen by the position of a marking on the knob, an array of sliders can give a visual impression of settings as in a graphic equalizer or faders on a mixing console . The resistive element of inexpensive potentiometers is often made of graphite . Other materials used include resistance wire, carbon particles in plastic, and

5372-450: The straight line nature of the physical sliding motion. The word linear when applied to a potentiometer regardless of being a slide or rotary type, describes a linear relationship of the pot's position versus the measured value of the pot's tap (wiper or electrical output) pin. Potentiometers were formerly used to control picture brightness, contrast, and color response. A potentiometer was often used to adjust "vertical hold", which affected

5451-435: The surface of the layer beneath it has a transparent resistive coating. A finger or stylus deforms the glass to contact the underlying layer. Edges of the resistive layer have conductive contacts. Locating the contact point is done by applying a voltage to opposite edges, leaving the other two edges temporarily unconnected. The voltage of the top layer provides one coordinate. Disconnecting those two edges, and applying voltage to

5530-448: The synchronization between the receiver's internal sweep circuit (sometimes a multivibrator ) and the received picture signal, along with other things such as audio-video carrier offset, tuning frequency (for push-button sets) and so on. It also helps in frequency modulation of waves. Potentiometers can be used as position feedback devices in order to create closed-loop control , such as in a servomechanism . This method of motion control

5609-469: The transmit buffer or shift register; "ready for next character(s)" may also be signaled with an interrupt. Transmitting and receiving UARTs must be set for the same bit speed, character length, parity, and stop bits for proper operation. The receiving UART may detect some mismatched settings and set a "framing error" flag bit for the host system; in exceptional cases, the receiving UART will produce an erratic stream of mutilated characters and transfer them to

5688-426: The turns of resistance wire. The "fingers" can be moved along the coil of resistance wire by a sliding knob thus changing the "tapping" point. Wire-wound rheostats made with ratings up to several thousand watts are used in applications such as DC motor drives, electric welding controls, or in the controls for generators. The rating of the rheostat is given with the full resistance value and the allowable power dissipation

5767-530: The two ends of the potentiometer. This is their most common use. The voltage across R L can be calculated by: V L = R 2 R L R 1 R L + R 2 R L + R 1 R 2 ⋅ V s . {\displaystyle V_{\mathrm {L} }={R_{2}R_{\mathrm {L} } \over R_{1}R_{\mathrm {L} }+R_{2}R_{\mathrm {L} }+R_{1}R_{2}}\cdot V_{s}.} If R L

5846-500: The voltage level, 2 UART modules work well when they both have the same voltage level, e.g 3V-3V between the 2 UART modules. To use 2 UART modules at different voltage levels, a level switch circuit needs to be added externally. A UART frame consists of 5 elements: In the most common settings of 8 data bits, no parity and 1 stop bit (aka 8N1 ), the protocol efficiency is 80%. For comparison, Ethernet 's protocol efficiency when using maximum throughput frames with payload of 1500 bytes

5925-450: The volume increased by turning the same knob. Multiple resistance elements can be ganged together with their sliding contacts on the same shaft, for example in stereo audio amplifiers for volume control. In other applications, such as domestic light dimmers , the normal usage pattern is best satisfied if the potentiometer remains set at its current position, so the switch is operated by a push action, alternately on and off, by axial presses of

6004-409: The wiper. Where the rheostat must be rated for higher power (more than about 1 watt), it may be built with a resistance wire wound around a semi-circular insulator, with the wiper sliding from one turn of the wire to the next. Sometimes a rheostat is made from resistance wire wound on a heat-resisting cylinder, with the slider made from a number of metal fingers that grip lightly onto a small portion of

6083-600: Was also an early hardware system for the Internet . A UART is usually an individual (or part of an) integrated circuit (IC) used for serial communications over a computer or peripheral device serial port . One or more UART peripherals are commonly integrated in microcontroller chips. Specialised UARTs are used for automobiles , smart cards and SIMs . A related device, the universal synchronous and asynchronous receiver-transmitter (USART) also supports synchronous operation. In OSI level terms, UART lives on layer 2,

6162-481: Was first used at Motorola around 1975 to refer to their start-stop asynchronous serial interface device, which others were calling a UART. Zilog manufactured a number of Serial Communication Controllers or SCCs. Starting in the 2000s, most IBM PC compatible computers removed their external RS-232 COM ports and used USB ports that can send data faster. For users who still need RS-232 serial ports, external USB-to-UART bridges are now commonly used. They combine

6241-630: Was the SCN2651 from the Signetics 2650 family. An example of an early 1980s UART was the National Semiconductor 8250 used in the original IBM PC 's Asynchronous Communications Adapter card. In the 1990s, newer UARTs were developed with on-chip buffers. This allowed higher transmission speed without data loss and without requiring such frequent attention from the computer. For example, the popular National Semiconductor 16550 has

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