US 5,490,209 A · 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.

Claims12

Dependent claims

For use with a serial data communications device having a serial port through which digital data messages are interfaced between a resident communications controller and a serial data communications link, to which a remote terminal device is coupled, a mechanism for establishing the baud rate of said serial communications device at the baud rate of a digital data message received from said remote terminal device comprising the steps of:

(a) initially setting the baud rate of said serial communications device to a default baud rate corresponding to the highest baud rate at which said serial communications device is operative to communicate with a remote terminal device;
(b) in response to an incoming call from a remote terminal device, examining respective bits of a received digital data stream for the presence of transmission errors;
(c) in response to step (b) detecting the presence of a transmission error, changing the baud rate from its current baud rate to a baud rate lower than the current baud rate, and monitoring said serial data communications link for digital data transmitted from said remote terminal device at said lower baud rate, but otherwise comparing the bit contents of said received digital data stream with a digital bit pattern associated with a prescribed reference character;
and
(d) in response to step (c) detecting a match between said received digital data stream and said digital bit pattern associated with said prescribed reference character, setting the baud rate of said serial communications device at the current baud setting for the remainder of the call, but otherwise changing the baud rate from its current baud rate to said lower baud rate, and repeating steps (b)-(d), until step (d) sets the baud rate of said serial communications device for the remainder of the call.

2 more elements

A serial data communications device having a serial port through which digital data messages are interfaced between a resident communications controller and a serial data communications link, to which a remote terminal device is coupled, said communications controller having its baud rate initially set to a default baud rate corresponding to the highest baud rate at which said serial communications device is capable of communicating with a remote terminal device, and being operative to establish the baud rate of said serial communications device at the baud rate of a digital data message received from said remote terminal device by means of a baud rate establishing routine which is operative to execute the following steps:

(a) in response to an incoming call from a remote terminal device, examining respective bits of a received digital data stream for the presence of transmission errors;
(b) in response to step (a) detecting the presence of a transmission error, changing the baud rate from its current baud rate to a baud rate lower than the current baud rate, and monitoring said serial data communications link for digital data transmitted from said remote terminal device at said lower baud rate, but otherwise comparing the bit contents of said received digital data stream with a digital bit pattern associated with a prescribed reference character;
and
(c) in response to step (b) detecting a match between said received digital data stream and said digital bit pattern associated with said prescribed reference character, setting the baud rate of said serial communications device at the current baud setting for the remainder of the call, but otherwise changing the baud rate from its current baud rate to said lower baud rate, and repeating steps (a)-(c), until step (c) sets the baud rate of said serial communications device for the remainder of the call.

1 more element

Dependencies are inferred from the claim text.

Autobaud rate detection mechanism

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Autobaud rate detection mechanism

Life of this patent

Abstract

Claims12