| 摘要 |
A communications card modem useful as an internal modem in a personal computer (PC) is configured with an autonomous power supply and an additional communications port for converting the modem into an external modem for a mobile user input device, such as a PDA. In a preferred embodiment, the autonomous power supply is an integrated rechargeable power source, such as a secondary battery like nickel-cadmium, nickel-metal-hydroxide or lithium-ion. The secondary battery is recharged by means of the computer power supply, during use of the computer, so that a user can remove the modem from the computer and still maintain an electrical power supply for the modem. Preferred communication ports for interfacing with the user input device include serial ports such as an EIA-232-D or an IrDA port. An isolation circuit within the modem is provided to determine whether the computer power supply or the autonomous power supply is to energize the modem circuitry. A switch, operable by the user, may additionally be included to indicate to the isolation circuitry which electrical power supply should energize the modem circuitry.
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