Autobaud rate detection mechanism

Abstract

An autobaud detection mechanism, installed as part of the communication control software of a serial communication device's microcontroller, enables the device to automatically determine the baud rate employed by a remote digital data communications device. Starting with a default baud rate, corresponding to the highest available baud rate, the mechanism steps through successively lower baud rates in the course of a search for the baud rate at which the remote device is transmitting. When an incoming call is received, respective bits of the received data are examined for the presence of transmission errors. If a transmission error is detected, the baud rate is stepped to the next lowest baud rate. If no error is detected, the received data bits are compared with a reference character. If the two compared data bit patterns match, the controller locks the baud rate at that baud setting for the remainder of the call. When the call is terminated, the baud rate reverts to its default setting. If the bit pattern comparison does not indicate a match, the baud rate is stepped to the next lowest baud rate. When the autobaud detection routine has stepped to a new baud rate entry, it initiates a prescribed time-out as a safeguard against the receiver becoming `out-of-sync` with a transmitter. Once, the lowest baud rate has been reached, the routine steps to the default setting and starts again.