| 摘要 |
An audit module (10) configured to monitor vending machine events when coupled to a vending machine (12) can transfer monitored vending machine information to a central station (16) via a telephone line (14). An interface circuit (18) is connected to the audit module and can be connected to the telephone line. The interface circuit includes circuitry (34) that can be activated by the audit module to sense caller identification signals on the telephone line without causing an off-hook condition and to provide the caller identification signals to the audit module (10). The audit module is configured to answer a call on the telephone line only if the audit module determines that the caller identification signals indicate that the call was initiated by the central station (16). The interface circuit (18) includes circuitry (34) that can be activated by the audit module (10) to sense whether the telephone line is in use without causing an off-hook condition and to provide one or more signals to the audit module indicative of whether the telephone line is in use. The audit module (10) is further configured to establish an off-hook condition and initiate a call to the central station (16) via the telephone line (14) only if the audit module determines that the telephone line is not in use.
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