Importance

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Abstract

A computer system having a power control unit for selection of voltage levels for pluggable cards, such as PCMCIA cards. The computer system includes a primary unit for executing two or more versions of control software (card drivers within the operating system) including a current version of control software. A pluggable PCMCIA card operates with a card voltage and has pins for signalling with a CD signal that the card is plugged into the computer system. The computer includes a power supply for providing at least first and second supply voltages such as 5 V, 3.3 V and x.x V. Power switches select one of the supply voltages as the card voltage. A power control unit controls the power switching unit to select one of the supply voltages. The power control unit includes a voltage select unit operable in response to the current version of the control software for storing a voltage code for specifying the selected one of the supply voltages. The power control unit includes a power enable unit operable to be set in response to the control software for enabling the voltage select unit and operable to be reset in the absence of the CD signal. The power control unit includes a code generating unit that in turn includes a synchronous unit operable in response to the control software for generating the voltage code and including a limit unit for limiting the voltage code to a maximum value and including asynchronous code generating unit operable in response to the CD signal for storing the voltage code in the voltage select unit.

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First Claim