Method to Inhibit Power Saving Modes on a Mobile Computer while Driving an External Display
Original Publication Date: 2002-Jan-16
Included in the Prior Art Database: 2003-Jun-20
Method to Inhibit Power Saving Modes on a Mobile Computer while Driving an External Display This publication describes a method to inhibit a mobile computer from entering a lower power state (that would disrupt the image being displayed) when the computer is driving an external display. Mobile computers today have external display interfaces so that they can drive external monitors or projectors. These external projectors are used to display the screen image which is typically a presentation being made in front of an audience or in a meeting. When the computer is running off of its battery it is customarily programmed to enter a low power state after some time of inactivity. This has the effect of disrupting or turning off the image being displayed. This can happen frequently since the presenter is rarely interacting with the computer (which resets the timers that trigger this) while making the presentation. This can be disruptive to the presenter and the audience. Using a mobile computer that uses this method to disable the turning off of the display will allow for more effective and pleasant presentations. The method described below solves the problem of a mobile computer that is driving an external display unwantingly turning off the display to go into a low power mode. Modern mobile computers have software utilities that are used to activate and de-activate the external display port. Once this port is enabled it transmits the exact same image that is being displayed (or would be displayed) on the built-in display. If the computer is running off the battery (as it may be in many cases when being used to make a presentation) it is programmed to enter a lower power state (and hence turn off the display) after some period of inactivity. This is done to conserve the battery. If the computer is being used to make a presentation this can be disruptive. Mobile computers today have software applications to control the signals outputted from the external display interface. Using the state of this software to control the power management scheme is not sufficient since most times the user does not know whether the external port is enabled or not. and the computer may not optimally enter the power saving states. The method described here detects whether the external display interface is really driving an external device and only overrides the power management state change when an external device is being driven. An identical resistor network is placed on each of the 3 color signals to keep the impedances the same. This is important to keep the colors balanced. A high impedance sense amp is used to detect a change in the loading current on any one of the 3 signals. When the loading goes above a specific threshhold the sense amp detects this. It signals the chip set that by setting a bit in a register that a device is physically present. Using a software power management (ACPI or similiar) driver that is triggered by the state change of this bit the system is not allowed to enter the lower power states (and hence disrupt the display). This affords the user a transparent way of assuring that the display will not be changed when the computer is attached to an external display device.