Patent ID: 7139243

Claim:
A data transmission method for placing variable-length transmission data in each frame having a fixed time length to transmit the frame, a length of the transmission data being one of two values, X (X≠0) and 0, the data transmission method comprising the steps of: at a transmitting side, calculating an error-detecting code of the transmission data in the frame only if the frame contains the transmission data; generating frame data containing the transmission data and the calculated error-detecting code of the transmission data if the frame contains the transmission data, and generating frame data that contains neither the transmission data nor the error-detecting code of the transmission data if the frame does not contain the transmission data; and transmitting the generated frame data; and at a receiving side, receiving the frame data; determining the transmission data and the error-detecting code of the transmission data by determining a predetermined position in the received frame data as the final bit position of the frame data, and calculating an error-detecting code based on the determined transmission data; deciding that the frame contains the transmission data if the determined error-detecting code matches the error-detecting code calculated based on the determined transmission data, and deciding that the frame data does not contain the transmission data or the received frame data contains an error if the determined error-detecting code does not match the calculated error-detecting code; and obtaining the transmission data in the frame based on the result of the decision, wherein at the receiving side, the step of determining and calculating determines the transmission data and the error-detecting code based on the final bit position where the length of the transmission data is X, and calculates the error-detecting code based on the determined transmission data, and wherein, at the transmitting side, the step of generating the frame data generates the frame data in which the error-detecting code is placed after the corresponding transmission data and the bits of the error-detecting code are arranged in the order that is the reverse of the order of the bits of the transmission data.