| 摘要 |
A GSM data unit 100 can be coupled with a palm-top computer 108 (or a PDA or laptop PC) which has its own power source. The data unit 100 has a battery 112 which can be connected by a switch 110 to an internal power supply line 116 for powering RF unit 102, base band unit 104 and modem 106 (eg. a PCMCIA circuit). On initially coupling the data unit 100 to the computer 108, a changeover switch 124 is in a position connecting low power circuitry within a controller 122 of modem 106 for powering from the power source within computer 108 via an interfacing terminal 128. On sensing the presence of voltage on supply line 126 from computer 108, modem controller 122 tests units 102 and 104. If the units 102, 104 are functioning correctly, the controller 122 closes the power switch 110 and switches the switch 124 to the power line 116 so that the battery 112 is used to supply power to the GSM data unit 100 instead of the source in computer 108. In response to a power down instruction, or in response to the GSM data unit 100 being unplugged from computer 108, a call processor 120 in unit 104 opens switch 110 to prevent further drain from battery 112, and the changeover switch 124 returns to the state in which interfacing terminal 128 is coupled to modem controller 122. |
