Pulse or digital communications – Transceivers – Modems
Reexamination Certificate
1998-11-13
2002-04-16
Pham, Chi (Department: 2631)
Pulse or digital communications
Transceivers
Modems
C708S212000
Reexamination Certificate
active
06373885
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates generally to the field of communications and, in particular, to a circuit and method for detecting an escape sequence.
BACKGROUND
In recent years, computers have become a commonplace part of life for large segments of society. Many businesses and other groups or institutions rely on vast networks of computers to share data among geographically dispersed users. To communicate with each other, these computers often include devices known as modems that allow computers to communicate with each other.
One type of modem is known colloquially as a “Hayes compatible” modem. This type of modem operates generally in one of two modes: a transparent or online mode and a command mode. In the command mode, data that is provided to the modem is interpreted as commands for the modem. In the transparent mode, the data received at an input to the modem is communicated out an output port and sent over a communication link to another modem. One problem in the design of these modems is how to instruct the modem when to switch from transparent mode to the command mode of operation.
U.S. Pat. No. 4,549,302 (the '302 Patent) refers to the use of an escape sequence to return from online mode to command mode. The escape sequence includes an escape command that is preceded by a period of silence, e.g., 1 second, and/or followed by a period of silence. The periods of silence in the escape sequence are used to prevent the modem from inadvertently entering into the command mode of operation. To detect this escape sequence, the modem includes a timer. The timer measures periods of silence in the data stream.
In an alternative to the technique of the '302 Patent, a time independent escape sequence (TIES) detection process has been developed. According to the TIES process, all characters received by the modem are monitored to detect receipt of the escape command. When a possible escape command is detected, the TIES process determines the escape command is followed by a valid command from the modem command set. If not, it is assumed that the characters are not part of an escape sequence and the modem stays in the online mode. If the escape command is followed by a valid command, then the modem switches to command mode.
One problem with the TIES detection process is that it is necessary to constantly monitor the data provided to the modem for the escape command. This requires a large amount of overhead processing.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for an improved circuit and method for controlling the operational mode of a modem.
SUMMARY OF THE INVENTION
The above mentioned problems with modems and other problems are addressed by the present invention and which will be understood by reading and studying the following specification. A circuit and method for detecting an escape sequence is described which uses the size of a data packet to determine when to send data to the TIES detection process thereby reducing the amount of data that is monitored by the TIES process. The TEES process is used only when the data in a message is small, e.g., three or fewer characters. Otherwise, the data received by the modem is sent directly out in the online mode of operation.
REFERENCES:
patent: 4549302 (1985-10-01), Heatherington
patent: 4926448 (1990-05-01), Kraul et al.
patent: 4928305 (1990-05-01), Yui
patent: 5107518 (1992-04-01), Petty, Jr.
patent: 5245560 (1993-09-01), Cunningham et al.
patent: 5295156 (1994-03-01), Heep et al.
patent: 5359648 (1994-10-01), Dunn et al.
patent: H1413 (1995-02-01), Gunn
patent: 5528626 (1996-06-01), Brigida et al.
patent: 5530718 (1996-06-01), Gradeler et al.
patent: 6151355 (2000-11-01), Vallee et al.
Digi International Inc.
Phu Phuong
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