System for accesssing a plurality of stations.

摘要

A system for unlocking any of several vehicles (10) by a passive electronic key (14) coupled to base units (12) in the vehicles (10) by a radio link uses short range LF transmission for signals to the key (14) and VHF transmission for signals to the base units (12). The key (14) has a ferrite antenna (38) connected to a receiver (36) comprising a comparator. When an operator pulls the door handle, codes stored in the base unit (12) are transmitted to identify any authorized key (14) within the range. The key (14) has a memory (50) partitioned into separate blocks for different base units (12) and another block for a scratchpad memory. A state machine (44) stores the block addresses and controls access to the blocks (50) according to the transmitted codes. When a block is accessed, a secure ID in the block is sent to the base unit (12) to verify that the key (14) is authorized to unlock the vehicle (10). The ID can be updated upon command from the base unit (12) using the same codes to assure that an authorized unit is receiving the new ID. The new ID is written to the scratchpad, verified for correctness, and the scratchpad address is exchanged for the address of the block containing the old ID. Auxiliary data specific to the vehicle (10) or to the user of the electronic key (14) may also be stored in the memory blocks (50) and retrieved along with the ID.