Serial port - Wikipedia. In computing, a serial port is a serial communication interface through which information transfers in or out one bit at a time (in contrast to a parallel port). Pinout of PC serial port (RS-232 DE9) and layout of 9 pin D-SUB male connector and 10 pin IDC male connectorThis RS232C DE-9 (usually miscalled DB-9) port is. An RS-232 serial port was once a standard feature of a personal computer. Y cables may be used to allow using another serial port to monitor all traffic on one. Serial ports are still used in applications such as industrial automation systems, scientific instruments, point of sale systems and some industrial and consumer products. Server computers may use a serial port as a control console for diagnostics. Network equipment (such as routers and switches) often use serial console for configuration. Serial ports are still used in these areas as they are simple, cheap and their console functions are highly standardized and widespread. A serial port requires very little supporting software from the host system. Hardware. This IC converts characters to and from asynchronous serial form, implementing the timing and framing of data in hardware. Very low- cost systems, such as some early home computers, would instead use the CPU to send the data through an output pin, using the bit- banging technique. Before large- scale integration (LSI) UART integrated circuits were common, a minicomputer or microcomputer would have a serial port made of multiple small- scale integrated circuits to implement shift registers, logic gates, counters, and all the other logic for a serial port. Early home computers often had proprietary serial ports with pinouts and voltage levels incompatible with RS- 2. Inter- operation with RS- 2. These make it possible to connect devices that would not have operated feasibly over slower serial connections, such as mass storage, sound, and video devices. Many personal computer motherboards still have at least one serial port, even if accessible only through a pin header. Small- form- factor systems and laptops may omit RS- 2. RS- 2. 32 has been standard for so long that the circuits needed to control a serial port became very cheap and often exist on a single chip, sometimes also with circuitry for a parallel port. DTE and DCE. Devices are divided into two categories . A line that is an output on a DTE device is an input on a DCE device and vice versa so a DCE device can be connected to a DTE device with a straight wired cable. Conventionally, computers and terminals are DTE while modems and peripherals are DCE. If it is necessary to connect two DTE devices (or two DCE devices but that is more unusual) a cross- over null modem, in the form of either an adapter or a cable, must be used. Drivers and Set-up for the USB RS-232 Adapter with Prolific Chipset; Home; Shop; My cart. The StarTech.com Advantage. Single cable USB to Serial and Parallel design enables two legacy devices to be connected to a host computer through a single USB port. USB RS232 - FTDI designs and supplies USB semiconductor devices with Legacy support including royalty-free drivers. Application areas include USB RS232, ( USB Serial. Male and female. However, there are many cases in which this does not apply; for instance, most serial printers have a female DB2. DTEs. The desire to supply serial interface cards with two ports required that IBM reduce the size of the connector to fit onto a single card back panel. A DE- 9 connector also fits onto a card with a second DB- 2. Centronics- style connector. Starting around the time of the introduction of the IBM PC- AT, serial ports were commonly built with a 9- pin connector to save cost and space. However, presence of a 9- pin D- subminiature connector is not sufficient to indicate the connection is in fact a serial port, since this connector is also used for video, joysticks, and other purposes. Below is a mating 3. P- CV connector. Some miniaturized electronics, particularly graphing calculators and hand- held amateur and two- way radio equipment, have serial ports using a phone connector, usually the smaller 2. Many models of Macintosh favor the related RS- 4. German Mini- DIN connectors, except in the earliest models. The Macintosh included a standard set of two ports for connection to a printer and a modem, but some Power. Book laptops had only one combined port to save space. Since most devices do not use all of the 2. For example, the 9- pin DE- 9 connector is used by most IBM- compatible PCs since the IBM PC AT, and has been standardized as TIA- 5. More recently, modular connectors have been used. Most common are 8. P8. C connectors, for which the EIA/TIA 5. P1. 0C connectors can be found on some devices as well. Digital Equipment Corporation defined their own DECconnect connection system which is based on the Modified Modular Jack (MMJ) connector. This is a 6- pin modular jack where the key is offset from the center position. As with the Yost standard, DECconnect uses a symmetrical pin layout which enables the direct connection between two DTEs. Another common connector is the DH1. DE- 9 connector (and frequently mounted on a free slot plate or other part of the housing). Pinouts. The ground signal is a common return for the other connections; it appears on two pins in the Yost standard but is the same signal. The DB- 2. 5 connector includes a second . Connecting this to pin 7 (signal reference ground) is a common practice but not essential. Note that EIA/TIA 5. DSR and RI. Unix- like operating systems usually label the serial port devices /dev/tty* (TTY is a common trademark- free abbreviation for teletype) where * represents a string identifying the terminal device; the syntax of that string depends on the operating system and the device. On Linux, 8. 25. 0/1. UART hardware serial ports are named /dev/tty. S*, USB adapters appear as /dev/tty. USB* and various types of virtual serial ports do not necessarily have names starting with tty. The Microsoft MS- DOS and Windows environments refer to serial ports as COM ports: COM1, COM2. Ports numbered greater than COM9 should be referred to using the \\.\COM1. This list includes some of the more common devices that are connected to the serial port on a PC. Some of these such as modems and serial mice are falling into disuse while others are readily available. Serial ports are very common on most types of microcontroller, where they can be used to communicate with a PC or other serial devices. Since the control signals for a serial port can be easily turned on and off by a switch, some applications used the control lines of a serial port to monitor external devices, without exchanging serial data. A common commercial application of this principle was for some models of uninterruptible power supply which used the control lines to signal . At least some Morse code training software used a code key connected to the serial port, to simulate actual code use. The status bits of the serial port could be sampled very rapidly and at predictable times, making it possible for the software to decipher Morse code. Settings. In modern serial ports using a UART integrated circuit, all settings are usually software- controlled; hardware from the 1. One of the simplifications made in such serial bus standards as Ethernet, Fire. Wire, and USB is that many of those parameters have fixed values so that users cannot and need not change the configuration; the speed is either fixed or automatically negotiated. Often if the settings are entered incorrectly the connection will not be dropped; however, any data sent will be received on the other end as nonsense. Serial ports use two- level (binary) signaling, so the data rate in bits per second is equal to the symbol rate in baud. A standard series of rates is based on multiples of the rates for electromechanical teleprinters; some serial ports allow many arbitrary rates to be selected. The port speed and device speed must match. The capability to set a bit rate does not imply that a working connection will result. Not all bit rates are possible with all serial ports. Some special- purpose protocols such as MIDI for musical instrument control, use serial data rates other than the teleprinter series. Some serial port systems can automatically detect the bit rate. The speed includes bits for framing (stop bits, parity, etc.) and so the effective data rate is lower than the bit transmission rate. For example, with 8- N- 1 character framing only 8. Bit rates commonly supported include 7. This is 1. 6 times the fastest bit rate and the serial port circuit can easily divide this down to lower frequencies as required. Data bits. 8 data bits are almost universally used in newer applications. Most serial communications designs send the data bits within each byte LSB (Least significant bit) first. This standard is also referred to as . To communicate with systems that require a different bit ordering than the local default, local software can re- order the bits within each byte just before sending and just after receiving. Parity is a method of detecting errors in transmission. When parity is used with a serial port, an extra data bit is sent with each data character, arranged so that the number of 1 bits in each character, including the parity bit, is always odd or always even. If a byte is received with the wrong number of 1s, then it must have been corrupted. However, an even number of errors can pass the parity check. Electromechanical teleprinters were arranged to print a special character when received data contained a parity error, to allow detection of messages damaged by line noise. A single parity bit does not allow implementation of error correction on each character, and communication protocols working over serial data links will have higher- level mechanisms to ensure data validity and request retransmission of data that has been incorrectly received. The parity bit in each character can be set to none (N), odd (O), even (E), mark (M), or space (S). None means that no parity bit is sent at all. Mark parity means that the parity bit is always set to the mark signal condition (logical 1) and likewise space parity always sends the parity bit in the space signal condition. Aside from uncommon applications that use the 9th (parity) bit for some form of addressing or special signalling, mark or space parity is uncommon, as it adds no error detection information. Odd parity is more useful than even, since it ensures that at least one state transition occurs in each character, which makes it more reliable. The most common parity setting, however, is . Electronic devices usually use one stop bit. If slow electromechanical teleprinters are used, one- and- one half or two stop bits are required.
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