| 摘要 |
<p>An identification system comprises an interrogator which transmits an interrogation signal to a plurality of transponders, each of which is arranged automatically to reply by means of a first coded identification signal stored in the transponder and modulated onto a carrier wave transmitted by the transponder. The interrogator receives and checks the reply signal. In the event of there being a plurality of transponders within range and broadcasting reply signals simultaneously, the interrogator receives corrupted reply signals. The interrogator therefore retransmits the reply signals to the transponders and each transponder checks the retransmitted reply signal with its first coded identification signal. In the event of correspondence the transponder discontinues transmission and in the event of non-correspondence the transponder continues transmission. In a polling mode of operation, the interrogator initially transmits a second coded identification signal corresponding to a selected transponder, and each transponder within the range compares the second signal with the first signal stored therein. If correspondence is established, the transponder is adjusted to receive further instructions which may comprise replacement of data stored therein. Each transponder includes a demodulator (34) comprising a phase locked loop which provides data, clock and carrier detect signals to a CPU (50) which includes ROM, RAM and an ALU. The carrier detect signal enables the CPU to switch the transponder from a power down condition to a power up conditon.</p> |
