US Patent 7133947 Data communication system, data communication method, and communication unit

A master provides a byte length of a frame in a certain position of the frame. The master also provides an error detection code in the final byte. After sending the final byte, the master monitors whether or not a negative acknowledgement is received. If a negative acknowledgment is received, the master transmits a dummy byte and then sends a stop condition. A slave counts the number of received bytes and compares the number of received bytes with the byte length of the frame. If the number of received bytes is larger than the byte length of the frame, the slave recognizes negative acknowledgement.