Method and apparatus for implementing an escape sequence
AssigneeHayes Microcomputer Products, Inc.
InventorsDouglas R. Kraul, Stuart A. Cox
Life of this patent
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Abstract
A multi-port message buffer which is responsive to an escape sequence. A control unit controls whether the message buffer is in a transparent mode or a command mode with respect to a particular port. The control unit monitors a data port for the escape sequence and, if the escape sequence is detected, the control unit causes the message buffer to enter into the command mode with respect to that port. The escape sequence is a break sequence of a predetermined period, followed within a predetermined time by a predetermined character at a predetermined data transmission speed. The escape sequence can therefore be detected even if the currently programmed data transmission speed for that particular port is unknown.
Claims18
In an asynchronous data communications device of the type which is operable at a plurality of different data transmission rates, having at least a first port for connecting said asynchronous data communications device to data terminal equipment and a second port for connecting said asynchronous data communications device to a data utilization circuit, and further having two distinct modes of operation:
- (a) a transparent mode of operation in which said data communications device provides output data signals to said second port, said output data signals corresponding to input data signals provided to said first port by said data terminal equipment;
- and
- (b) a command mode of operation in which said data communications device responds to said input data signals provided to said first port by said data terminal equipment as instructions to said data communications device;
- an improved escape apparatus, operable when said data communications device is in said transparent mode of operation, comprising:
- detection means connected to said first port for detecting each occurrence of provision of a break signal to said first port by said data terminal equipment;
- and
- timing means responsive to said detection means for providing a time out signal in response to each occurrence of said detection means detecting said break signal for at least a predetermined period of time;
- wherein said detection means is further responsive to said time out signal and said input data signals to cause said data communications device to switch to said command mode of operation if said input data signals following termination of said break signal corresponds to a predetermined character transmitted at a particular one of said plurality of different data transmission rates, and otherwise causes said data communications device to remain in said transparent mode of operation.
In an asynchronous data communications device of the type which is operable at a plurality of different data transmission rates, having at least a first port for connecting said asynchronous data communications device to data terminal equipment and a second port for connecting said asynchronous data communications device to a data utilization circuit, and further having two distinct modes of operation:
- (a) a transparent mode of operation in which said data communications device provides output data signals to said second port, said output data signals corresponding to input data signals provided to said first port by said data terminal equipment;
- and
- (b) a command mode of operation in which said data communications device responds to said input data signals provided to said first port by said data terminal equipment as instructions to said data communications device;
- an improved method for escaping said apparatus from said transparent mode of operation to said command mode of operation, comprising the steps of:
- detecting each occurrence of provision of a break signal to said first port by said data terminal equipment;
- providing a time out signal in response to each occurrence of said break signal for at least a predetermined period of time;
- and
- responding to said time out signal and said input data signals by causing said data communications device to switch to said command mode of operation if said input data signals following termination of said break signal corresponds to a predetermined character transmitted at a particular one of said plurality of different data transmission rates, and otherwise causing said data communications device to remain in said transparent mode of operation.
Dependencies are inferred from the claim text.