| 摘要 |
<p>A key operated switch for an electrical circuit, e.g. the ignition circuit of a vehicle comprises a removable key (10 - 12, 14, 17) and a socket (15, 16) arranged to receive the key. The key includes a programmable read-only memory (20) with electrical contact elements (12) which co-operate with contacts in the socket to provide an addressing circuit from the socket to the memory in the key and also to provide power supply connections to the memory from supply terminals in the socket. The addressing circuit includes a multiplexer (26) to serialise data read from the memory. In the socket or in the housing therefor or electrically connected thereto is a second read-only memory (45) with a digital comparator (49). The two memories are addressed to feed data simultaneously from corresponding addresses to the comparator in sequence and circuit means (50, 51, 54, 55) operative on completion of a cycle of data comparison to effect operation of a relay (56) only if the compared data in the two memories (20, 45) agree. Thus the relay can only be operated if a key having a correctly programmed read-only memory is inserted in the socket. </p> |
