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Automatic baud rate detection (ABR, autobaud) refers to the process by which a receiving device (such as a modem) determines the speed, code level, start bit, and stop bits of incoming data by examining the first character, usually a preselected sign-on character (syncword) on a UART connection. ABR allows the receiving device to accept data from a variety of transmitting devices operating at different speeds without needing to establish data rates in advance.
During the autobaud process, the baud rate of received character stream is determined by examining the received pattern and its timing, and the length of a start bit. These type of baud rate detection mechanism are supported by many hardware chips including processors such as STM32 [1] MPC8280, MPC8360, and so on.
When start bit length is used to determine the baud rate, it requires the character to be odd since UART sends LSB bit first –this particular bit order scheme is referred to as little-endian. [2] Often symbols 'a' or 'A' (0x61 or 0x41) are used. For example, the MPC8270 SCC tries to detect the length of the UART start bit for autobaud.
Many protocols begin each frame with a preamble of alternating 1 and 0 bits that can be used for automatic baud rate detection. For example, the TI PGA460 uses a 'U' ( 0x55 ) sync byte for automatic baud rate detection as well as frame synchronization, [3] and so does the LIN header (Local Interconnect Network#Header).
For example, the UART-based FlexWire protocol begins each frame with a 'U' (0x55) sync byte. FlexWire receivers use the sync byte to precisely set their UART bit-clock frequency without a high-precision oscillator. [4] For example, the Ethernet preamble contains 56 bits of alternating 1 and 0 bits for synchronizing bit clocks.
Most modems currently on the market support autobaud. Before receiving any input data, most modems use a default baud rate of 9600 for output. For example, the following modems have been verified for autobaud and default output baud rate 9600:
The baud rate of modems are adjusted automatically after receiving input data by the autobaud process.
The 16550 UART is an integrated circuit designed for implementing the interface for serial communications. The corrected -A version was released in 1987 by National Semiconductor. It is frequently used to implement the serial port for IBM PC compatible personal computers, where it is often connected to an RS-232 interface for modems, serial mice, printers, and similar peripherals. It was the first serial chip used in the IBM PS/2 line, which were introduced in 1987.
A universal asynchronous receiver-transmitter is a peripheral device for asynchronous serial communication in which the data format and transmission speeds are configurable. It sends data bits one by one, from the least significant to the most significant, framed by start and stop bits so that precise timing is handled by the communication channel. The electric signaling levels are handled by a driver circuit external to the UART. Common signal levels are RS-232, RS-485, and raw TTL for short debugging links. Early teletypewriters used current loops.
A serial port is a serial communication interface through which information transfers in or out sequentially one bit at a time. This is in contrast to a parallel port, which communicates multiple bits simultaneously in parallel. Throughout most of the history of personal computers, data has been transferred through serial ports to devices such as modems, terminals, various peripherals, and directly between computers.
The data link layer, or layer 2, is the second layer of the seven-layer OSI model of computer networking. This layer is the protocol layer that transfers data between nodes on a network segment across the physical layer. The data link layer provides the functional and procedural means to transfer data between network entities and may also provide the means to detect and possibly correct errors that can occur in the physical layer.
Asynchronous serial communication is a form of serial communication in which the communicating endpoints' interfaces are not continuously synchronized by a common clock signal. Instead of a common synchronization signal, the data stream contains synchronization information in form of start and stop signals, before and after each unit of transmission, respectively. The start signal prepares the receiver for arrival of data and the stop signal resets its state to enable triggering of a new sequence.
In telecommunications and computing, bit rate is the number of bits that are conveyed or processed per unit of time.
LIN is a network protocol used for communication between components in modern vehicles. It is a low-cost single-wire serial protocol that supports communications up to 19.2 Kbit/s with a maximum bus length of 40 metres (131.2 ft).
Throughput of a network can be measured using various tools available on different platforms. This page explains the theory behind what these tools set out to measure and the issues regarding these measurements.
Synchronous and asynchronous transmissions are two different methods of transmission synchronization. Synchronous transmissions are synchronized by an external clock, while asynchronous transmissions are synchronized by special signals along the transmission medium.
A universal synchronous and asynchronous receiver-transmitter 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.
In computer science, a data buffer is a region of memory used to store data temporarily while it is being moved from one place to another. Typically, the data is stored in a buffer as it is retrieved from an input device or just before it is sent to an output device ; however, a buffer may be used when data is moved between processes within a computer, comparable to buffers in telecommunication. Buffers can be implemented in a fixed memory location in hardware or by using a virtual data buffer in software that points at a location in the physical memory.
In a digitally modulated signal or a line code, symbol rate, modulation rate or baud rate is the number of symbol changes, waveform changes, or signaling events across the transmission medium per unit of time. The symbol rate is measured in baud (Bd) or symbols per second. In the case of a line code, the symbol rate is the pulse rate in pulses per second. Each symbol can represent or convey one or several bits of data. The symbol rate is related to the gross bit rate, expressed in bits per second.
CANopen is a communication protocol stack and device profile specification for embedded systems used in automation. In terms of the OSI model, CANopen implements the layers above and including the network layer. The CANopen standard consists of an addressing scheme, several small communication protocols and an application layer defined by a device profile. The communication protocols have support for network management, device monitoring and communication between nodes, including a simple transport layer for message segmentation/desegmentation. The lower level protocol implementing the data link and physical layers is usually Controller Area Network (CAN), although devices using some other means of communication can also implement the CANopen device profile.
The Microcom Networking Protocols, almost always shortened to MNP, is a family of error-correcting protocols commonly used on early high-speed modems. Originally developed for use on Microcom's own family of modems, the protocol was later openly licensed and used by most of the modem industry, notably the "big three", Telebit, USRobotics and Hayes. MNP was later supplanted by V.42bis, which was used almost universally starting with the first V.32bis modems in the early 1990s.
In computer networks, a syncword, sync character, sync sequence or preamble is used to synchronize a data transmission by indicating the end of header information and the start of data. The syncword is a known sequence of data used to identify the start of a frame, and is also called reference signal or midamble in wireless communications.
ccTalk is a serial protocol in widespread use throughout the money transaction and point-of-sale industry. Peripherals such as the currency detectors for coins and banknotes found in a diverse range of automatic payment equipment such as transportation, ticketing, payphones, amusement machines, and retail cash management use ccTalk to talk to the host controller. The ccTalk protocol is an open standard.
M-Bus or Meter-Bus is a European standard for the remote reading of water, gas or electricity meters. M-Bus is also usable for other types of consumption meters, such as heating systems or water meters. The M-Bus interface is made for communication on two wires, making it cost-effective. A radio variant of M-Bus Wireless M-Bus is also specified in EN 13757–4.
The Serial Low-power Inter-chip Media Bus (SLIMbus) is a standard interface between baseband or application processors and peripheral components in mobile terminals. It was developed within the MIPI Alliance, founded by ARM, Nokia, STMicroelectronics and Texas Instruments. The interface supports many digital audio components simultaneously, and carries multiple digital audio data streams at differing sample rates and bit widths.
The SCC, short for Serial Communication Controller, is a family of serial port driver integrated circuits made by Zilog. The primary members of the family are the Z8030/Z8530, and the Z85233.