| 摘要 |
A full-featured data access arrangement (DAA) for connecting a modem to a public switched telephone network (PSTN) includes a bridge current loop circuit, a line in use detection circuit, an off hook relay, a loop current sense circuit, and an extension/remote event detector circuit. The off hook relay is connected in series with the current loop circuit to enable the DAA to detect external off hook and on hook events when the modem is in an on hook state. The DAA is configured to detect the off hook and subsequent on hook status of an extension telephone at a location even though the modem and a handset sharing a line connector with the modem are both in an on hook state. The DAA is also capable of detecting an off hook state of an extension telephone even though the modem is in an off hook state. In addition, the DAA can detect when a remote telephone device that initiates an incoming call is placed on hook.
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