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Power Button Functionality On The Latitude CP - Technical Tip - 152493

Power Button Functionality On The Latitude™ CP

The Latitude CP power switch is similar to previous products with some minor, but important modifications. The most significant modification is operating system notification. This feature will, in the future, be required by Microsoft to obtain certification under the PC 97 and ACPI specifications. These specifications entail that the system BIOS must notify the operating system that the power switch has been pressed and must allow the OS to follow its standard shutdown procedure prior to actual removal of system power. The OS will have the capability of delaying or even aborting the power down sequence until the operating system shutdown sequence or any other necessary processes have been completed.

Because of this new "power down authorization" principal, there arises some potential for additional problems to occur. If, for example, the operating system is somehow unable to respond to the system BIOS request for power down, a mechanism must be put in place to allow the user to override the OS shutdown authorization requirement.

For the Latitude CP, the power down override will be achieved by depressing the power switch for 4 seconds. If the system BIOS detects that the power switch has been active for a continuous 4 second duration, the system will immediately and unconditionally power down.

Please note: As of the date of this specification, Microsoft has not finalized or published the callback mechanism that must be implemented in the system BIOS to support this feature under any non-ACPI operating systems, including Windows 95. Please note that this feature is not adequately documented in the ACPI specification). Because of this, the OS notification will be supported on the Windows 98 ACPI implementation only.

During operation on non-ACPI operating systems, the power switch behavior may be generalized by the following two conditions: When the system is running in the normal operational (full on) state, depressing the power switch will cause the system to power down. When the system is currently operating in any power management state in which the LCD display is blank (standby, suspend, or suspend-to-disk), depressing the power switch will cause the system to return to the normal operational (full on) state.


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Article ID: SLN68889

Last Date Modified: 11/13/2010 12:00 AM

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