Automatic baud rate detection

Automatic baud rate detection on UART (ABR, autobaud) refers to the process by which a receiving device (such as a modem) determines the speed, code level, and stop bits of incoming data by examining the first character, usually a preselected sign-on character (syncword). 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 determinted 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 MPC8280, MPC8360, and so on.

Most of modems seen in market at this time support autobaud. Before receiving any input data, most modem use a default baud rate 9600 for default output baud rate. For example, the following modems have been verified for autobaud and default output baud rate 9600.

• USRobotics USR5686G 56K Serial Controller Fax modem
• Hayest V92 External modem
• microcom DeskPorte 28.8P

The baud rate of modems are adjusted automatically after receiving input data by autobaud process.

See also

• Telecommunications

References

This article is based on material taken from the Free On-line Dictionary of Computing prior to 1 November 2008 and incorporated under the "relicensing" terms of the GFDL, version 1.3 or later.

• "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" http://www.ti.com/lit/an/slaa215/slaa215.pdf
• "How to implement “auto baud rate detection” feature on Cortex-M3" http://stackoverflow.com/questions/38979647/how-to-implement-auto-baud-rate-detection-feature-on-cortex-m3