Pulse or digital communications – Miscellaneous
Reexamination Certificate
1997-09-29
2001-03-06
Pham, Chi H. (Department: 2631)
Pulse or digital communications
Miscellaneous
Reexamination Certificate
active
06198785
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of communications and in particular, to baudrate detection and adjustment between communication devices.
BACKGROUND OF THE INVENTION
Serial data communication devices are capable of transmitting and receiving data between various destinations at multiple data rates or baudrates. For example, modems normally operate at baudrates of 2400, 4800, 9600 and higher. Since communication devices can operate at any one of these various baudrates, there must be a method for selecting the baudrate that is being utilized by the destination device. This synchronization is required for the proper transfer of the data from one device to another. In some devices, the required baudrate is selectable by the user. A drawback of this method is that the user has to know the baudrate being used by the connecting device.
Autobauding is an alternative method for automatically determining and setting the correct baudrate at the serial data communication device. Some early devices employed circuitry which recognized the zero slope points of the received analog waveform and varied the transmission rates based on the presence or absence of information. However, these devices were not accurate. Most autobauding techniques measure the duration or width of a start bit. This method requires that the data stream be initially sampled at the highest possible bit rate. Then, by counting the number of zero bits read, the data rate is determined. A disadvantage of prior art methods using variants of this technique is that the character used for detection is lost. Moreover, prior art software-based methods are difficult to implement at speeds greater than 19.2 kbits per second.
Other prior art methods compare the incoming received data bits to a reference character by stepping through the different baudrates until no errors are present. However, these schemes also appear to lose some of the initial bits while trying to ascertain the baudrate. Some prior art devices utilize alternative hardware configurations to detect and determine the correct baudrate. However, the cost of additional hardware is expensive when dealing with thousands of modems.
Accordingly, there is a need to provide a simple and effective device and method which does not require additional hardware and can autobaud without loss of data bits.
SUMMARY OF THE INVENTION
The present invention teaches an apparatus and method for autobauding which utilizes firmware to automatically detect and adjust to the incoming baudrate from a data terminal. This method measures the width of the start bit but importantly, the present invention sets the proper baudrate without the loss of any characters in the data stream.
In an exemplary embodiment of the present method, a data communication device includes a controller and a baud rate generator, which is initially set to receive a data stream at the highest baudrate. In response to a start bit in the data stream, the controller suspends the operation of the baud rate generator and determines the proper baudrate by polling for the presence or absence of the start bit. During the suspended period, the baud rate generator is set to the actual incoming baudrate. The baud rate generator is then turned on, and the rest of the characters are then received at the actual baudrate. Importantly, the method of the present invention advantageously utilizes the execution times of background processing instructions to serve as the polling times. As such, the present invention prevents the loss of data bits since all baudrate determinations are completed during the receipt of the start bit.
Advantageously, a non-preemptive interrupt processor is utilized to detect the presence of the start bit, cause suspension of the baud rate generator and determine the actual baudrate. As such, the method and apparatus of the present invention can be utilized in any serial data communication device. The above factors make the present invention a versatile and efficient method and device for autobauding in data communication devices.
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Gibbons Del Deo Dolan Griffinger & Vecchione
Lucent Technologies - Inc.
Pham Chi H.
Tran Khai
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