| 摘要 |
The invention includes a method for transferring user data between a first data communications device and a second data communications device over a data link. The first data communications device transmits a DLE-BEL to the second data communications device to request initialization. The second data communications device transmits a DLE-SI to the first data communications device in response to the DLE-BEL to indicate initialization to receive the user data. The first data communications device transmits a DLE-STX to the second data communications device in response to the DLE-SI to identify the start of a frame of user data. The first data communications device transmits at least a portion of the user data to the second data communications device after transmitting the DLE-STX. The first data communications device transmits a frame-ending control code to the second data communications device after transmitting the user data. The frame-ending control code is either a DLE-ETB, DLE-ETX, or DLE-ESC. A DLE-ETB indicates an end to the frame with more frames to come. A DLE-ETX indicates an end to the frame and to the data transaction. A DLE-ESC indicates an end to the frame and a line-turn. The first data communications device transmits check values to the second data communications device. The second data communications device transmits a DLE-p or a DLE-a to the first data communications device in response to processing the check values to acknowledge that the frame of user data is error-free.
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