Universal asynchronous receiver/transmitter

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"DUART" redirects here. For the castle on the Island of Mull, see Duart Castle.
A universal asynchronous receiver/transmitter (usually abbreviated UART and pronounced /?ju??rt/) is a type of "asynchronous receiver/transmitter", a piece of computer hardware that translates data between parallel and serial forms. UARTs are commonly used in conjunction with other communication standards such as EIA RS-232.
A UART is usually an individual (or part of an) integrated circuit used for serial communications over a computer or peripheral device serial port. UARTs are now commonly included in microcontrollers. A dual UART or DUART combines two UARTs into a single chip. Many modern ICs now come with a UART that can also communicate synchronously; these devices are called USARTs.
Contents
1 Definition
1.1 Transmitting and receiving serial data
1.2 Asynchronous receive and transmit
1.3 Serial to Parallel Algorithm
2 History
3 Structure
4 Special Receiver Conditions
4.1 Overrun Error
4.2 Underrun Error
4.3 Framing Error
4.4 Parity Error
4.5 Break Condition
5 Baudrate
6 See also
7 External links
//
Definition
Transmitting and receiving serial data
Serial transmission of digital information (bits) through a single wire or other medium is much more cost effective than parallel transmission through multiple wires. A UART is used to convert the transmitted information between its sequential and parallel form at each end of the link. Each UART contains a shift register which is the fundamental method of conversion between serial and parallel forms.
The UART usually does not directly generate or receive the external signals used between different items of equipment. Typically, separate interface devices are used to convert the logic level signals of the UART to and from the external signaling levels.
External signals may be of many different forms. Examples of standards for voltage signaling are RS-232, RS-422 and RS-485 from the EIA. Historically, the presence or absence of current (in current loops) was used in telegraph circuits. Some signaling schemes do not use electrical wires. Examples of such are optical fiber, IrDA (infrared), and (wireless) Bluetooth in its Serial Port Profile (SPP). Some signaling schemes use modulation of a carrier signal (with or without wires). Examples are modulation of audio signals with phone line modems, RF modulation with data radios, and the DC-LIN for power line communication.
Communication may be "full duplex" (both send and receive at the same time) or "half duplex" (devices take turns transmitting and receiving).
As of 2008, UARTs are commonly used with RS-232 for embedded systems communications. It is useful to communicate between microcontrollers and also with PCs. Many chips provide UART functionality in silicon, and low-cost chips exist to convert logic level signals (such as TTL voltages) to RS-232 level signals (for example, Maxim's MAX232).
Asynchronous receive and transmit
In asynchronous transmitting, teletype-style UARTs send a "start" bit, five to eight data bits, least-significant-bit first, an optional "parity" bit, and then one, one and a half, or two "stop" bits. The start bit is the opposite polarity of the data-line's idle state. The stop bit is the data-line's idle state, and provides a delay before the next character can start. (This is called asynchronous start-stop transmission). In mechanical teletypes, the "stop" bit was often stretched to two bit times to give the mechanism more time to finish printing a character. A stretched "stop" bit also helps resynchronization.
The parity bit can either make the number of "one" bits between any start/stop pair odd, or even, or it can be omitted. Odd parity is more reliable because it assures that there will always be at least one data transition, and this permits many UARTs to resynchronize.
In synchronous transmission, the clock data is recovered separately from the data stream and no start/stop bits are used. This improves the efficiency of transmission on suitable channels since more of the bits sent are usable data and not character framing. An asynchronous transmission sends no characters over the interconnection when the transmitting device has nothing to send -- only idle stop bits; but a synchronous interface must send "pad" characters to maintain synchronism between the receiver and transmitter. The usual filler is the ASCII "SYN" character. This may be done automatically by the transmitting device.
USART chips have both synchronous and asynchronous modes.
Serial to Parallel Algorithm
A data communication pulse can only be in one of two states but there are many names for the two states. When on, circuit closed, low voltage, current flowing, or a logical zero,...(and so on) To get More information , you can visit some products about GPS External Antenna, Dish Satellite Receiver, . The free to air satellite receiver(pansat) products should be show more here!