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.
Supportedit
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:
USRobotics USR5686G 56K Serial Controller Fax modem
Hayes V92 External modem
Microcom DeskPorte 28.8P
The baud rate of modems are adjusted automatically after receiving input data by the autobaud process.
automatic, baud, rate, detection, this, article, includes, list, general, references, lacks, sufficient, corresponding, inline, citations, please, help, improve, this, article, introducing, more, precise, citations, march, 2013, learn, when, remove, this, temp. This article includes a list of general references but it lacks sufficient corresponding inline citations Please help to improve this article by introducing more precise citations March 2013 Learn how and when to remove this template message 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 Contents 1 Process 2 Support 3 See also 4 ReferencesProcess editDuring 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 Support editMost 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 USRobotics USR5686G 56K Serial Controller Fax modem Hayes V92 External modem Microcom DeskPorte 28 8PThe baud rate of modems are adjusted automatically after receiving input data by the autobaud process See also editAutonegotiation TelecommunicationsReferences edit STM32 USART automatic baud rate detection MIT 6 111 Introductory Digital Systems Laboratory PDF MIT 6 111 Fall 2019 Retrieved July 15 2023 Sync Field section of PGA460 Ultrasonic Signal Processor and Transducer Driver 2017 p 35 Texas Instruments TPS929121 Q1 12 Channel Automotive 40 V High Side LED Driver With FlexWire 2021 p 37 and p p 39 17 2 Autobaud Operation on a UART in MPC8280 PowerQUICC II Family Reference Manual http www nxp com files netcomm doc ref manual MPC8280RM pdf Automatic Baud Rate Detection on the MSP430 https web archive org web 20161026080239 http www ti com lit an slaa215 slaa215 pdf How to implement auto baud rate detection feature on Cortex M3 https stackoverflow com q 38979647 mpc8270 SCC2 UART issue https community nxp com message 906833 Retrieved from https en wikipedia org w index php title Automatic baud rate detection amp oldid 1187254525, wikipedia, wiki, book, books, library,
