| 摘要 |
A restrictive access control system includes a 3-state switch for controlling the operating mode of the system and limiting tuning access to only designated channels. Tuning information is provided to a microprocessor via a control panel keyboard for storage in a nonvolatile memory and for subsequent recall therefrom when desired channel information is entered in the control panel by a viewer. In one embodiment, a 3-position key actuated switch has a first OFF position, a second PROGRAM position, and a third ON position. In the ON and OFF positions, the key may be removed from the switch while in the second PROGRAM position the key may not be removed from the switch. Programming of the nonvolatile memory may only be accomplished with the key in second PROGRAM position for storing either desired channels or locking out undesired channels. From the second PROGRAM position, the key may be turned to either the first OFF position for viewing all available channels or to the third ON position whereupon only authorized channels can be viewed. Turning the switch between the various positions, or modes of operation, is not possible without the key so as to provide a high level of viewing security, while affording the key bearer not only channel programming access, but also the capability of limiting tuning access to only designated channels. Other embodiments include (1) a two position key switch with key detector and limited access control selector and (2) program and limited access control selectors in combination with an optical card reader.
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