| 摘要 |
A transmitter 20 is provided for transmitting a command signal, the transmitter including a rolling code generator 26 operable in response to a control logic 22 to provide a code forming at least part of said transmitted signal. The code is automatically changeable at intervals. A receiver 30 is provided which receives the transmitted signal for operating a vehicle lock. The receiver includes a rolling code generator 34 operable in response to a control logic 35 to provide a code associated with or related to the transmitted code and automatically changeable at intervals substantially in synchronism with the timing of code changes in the transmitter 20. The receiver is arranged to operate the security device even if the codes in the transmitter and receiver are up to a certain number of steps out of synchronism, that number increasing with time. The code change interval is notified to the receiver by the transmitter, and may itself change. <IMAGE> |
