Abstract: This invention allows a toll authority to monitor transaction numbers which are sent from a transponder (14) to an interrogator (12). By incrementing the transaction counter stored in the transponder with successful transactions the toll authority can ascertain whether accounting of a transaction has been missed (i.e., a transaction number missing from the sequence), or double-counted (i.e., two transactions with the same transaction number).

Abstract: This invention allows a toll authority to monitor transaction numbers which are sent from a transponder (14) to an interrogator (12). By incrementing the transaction counter stored in the transponder with successful transactions the toll authority can ascertain whether accounting of a transaction has been missed (i.e., a transaction number missing from the sequence), or double-counted (i.e., two transactions with the same transaction number).

Abstract: A system and method in which a transponder (14) is operable to transmit an original user account balance to an interrogator (12), which in turn calculates a revised user account balance and transmits the revised user account balance to the transponder (14). In one embodiment of the invention, the transponder (14) is further operable to transmit a verification user account balance back to the interrogator (12), which then compares verification user account balance to the revised user account balance that was earlier calculated and stored in an interrogator memory.

Abstract: A method and system is provided for communicating permanent or semi-permanent information to a transponder (14) from an interrogator (12), preferably operated by a toll agency or other authorized entity. This permanent or semi-permanent information is communicated by means of special instructions valid only during a special mode or maintenance mode which is entered by transmitting a special access code to the transponder (14) from the authorized interrogator (12). The transponder (14) will preferably acknowledge to the authorized interrogator (12) that it is, in fact, operating in the maintenance mode so the interrogator (12) can transmit the special instructions in confidence.

Abstract: A system and method which conserves energy in the operation of a transponder or tag (14) by providing that the transponder (14) be enabled or awakened in multiple stages. A threshold detector (62) is provided which measures the power level of received RF energy. If the RF energy received by the detector (62) exceeds a pre-determined level, the transponder (14) then employs a modulation detector (64) to ascertain whether it has been awakened by a valid interrogation signal from an interrogator (12) or whether the RF energy received was merely a spurious burst of RF energy from some other source. If a pre-determined modulation is detected by the modulation detector (64), the transponder (14) is then fully activated to its normal operational state.

Abstract: This invention allows a user to have a smartcard (66) and a smartcard-based transponder (14). This smartcard-based transponder (14) can accept money from the smartcard (14). The amount transferred from the smartcard (66) can be stored in the transponder memory (80,82). At a toll plaza (29), a toll amount can be subtracted within a short period of time, so that a vehicle (26) bearing the transponder (14) will not pass through the zone in which the transponder (14) and the interrogator (12) may perform RF communications before an appropriate toll amount can be decremented from the amount stored within the transponder (14).

Abstract: A transponder interface circuit (172) operates to allow communication between a transponder controller (104) and external circuitry. The interface circuit (172) has a buffer memory (184,186) that allows the transponder controller (104) and the external circuitry each to transmit data at either the transponder's (14) or the external circuitry's clock rate without complicated protocols for direct communication. Each of the transponder controller (104) and the external circuit may be enabled by an interface controller (174) to assume control of the buffer memory (184,186). By using the buffer memory (184,186) and interface controller (174), whichever of the transponder controller (104) and the external circuitry is transmitting or receiving data may fill or empty the buffer memory (184,186) at either the transponder controller's (104) or the external circuitry's chosen clock rate.

Abstract: A transponder interface circuit (172) operates to allow communication between a transponder controller (104) and external circuitry. The interface circuit (172) has a buffer memory (184,186) that allows the transponder controller (104) and the external circuitry each to transmit data at either the transponder's (14) or the external circuitry's clock rate without complicated protocols for direct communication. Each of the transponder controller (104) and the external circuit may be enabled by an interface controller (174) to assume control of the buffer memory (184,186). By using the buffer memory (184,186) and interface controller (174), whichever of the transponder controller (104) and the external circuitry is transmitting or receiving data may fill or empty the buffer memory (184,186) at either the transponder controller's (104) or the external circuitry's chosen clock rate.

Abstract: A system and method which conserves energy in the operation of a transponder or tag (14) by providing that the transponder (14) be enabled or awakened in multiple stages. A threshold detector (62) is provided which measures the power level of received RF energy. If the RF energy received by the detector (62) exceeds a pre-determined level, the transponder (14) then employs a modulation detector (64) to ascertain whether it has been awakened by a valid interrogation signal from an interrogator (12) or whether the RF energy received was merely a spurious burst of RF energy from some other source. If a pre-determined modulation is detected by the modulation detector (64), the transponder (14) is then fully activated to its normal operational state.

Abstract: A method and system is provided for communicating permanent or semi-permanent information to a transponder (14) from an interrogator (12), preferably operated by a toll agency or other authorized entity. This permanent or semi-permanent information is communicated by means of special instructions valid only during a special mode or maintenance mode which is entered by transmitting a special access code to the transponder (14) from the authorized interrogator (12). The transponder (14) will preferably acknowledge to the authorized interrogator (12) that it is, in fact, operating in the maintenance mode so the interrogator (12) can transmit the special instructions in confidence.