| 摘要 |
A transmitter 20 includes a rolling code generator 26 to provide a code forming at least part of a transmitted command signal. The code is automatically changeable at intervals. A receiver 30 also includes a rolling code generator 34 to provide a code associated with or related to the transmitted code to facilitate operation of a security device. The code in the receiver 30 is also automatically changeable at intervals substantially in synchronism with the timing of code changes in the transmitter 20. The intervals between code changes increases with time so as to accommodate a gradual de-synchronization of clocks 25,33 in the transmitter and receiver. |
