Abstract:
A dual display mode portable computer is disclosed. The portable computer includes a flat-panel display, and a display controller for outputting an internal video signal to the flat panel display. The portable computer further includes means for receiving an external video signal, and a multiplexer for outputting the internal video signal to the flat-panel display during a first display mode, and for outputting the external video signal to the flat-panel display during a second display mode, thereby enabling the portable computer to act as a display device for an external computer.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present invention is a Divisional Application of U.S. Application Ser. No. 10/055,244, entitled “Display Controller Architecture for Portable Computers” filed on Oct. 26, 2001, now U.S. Pat. No. 6,873,306, and incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to portable computers, and more particularly to a display controller architecture for portable computers. 
     BACKGROUND OF THE INVENTION 
     Laptops and notebooks are names for portable computers that have a flat screen and usually weigh less than eight pounds. Most portable computers have connectors for an external monitor and keyboard for transforming them into desktop computers. 
       FIG. 1  is a block diagram illustrating current display technology found in portable computers. Like most computer systems, a portable computer  10  includes internal hardware and software  12  for operating the system, and a display controller  14  for outputting an internal video signal  16  to a flat panel display  18 . The portable computer  10  also includes a digital-to-analog converter  20  and an external CRT connector  22  for outputting the video signal  16  to an external monitor, such as a cathode ray tube (CRT) (not shown). With this type of display architecture, the portable computer  10  is capable of outputting its video signal on the flat-panel display  18 , on the external CRT, or on both the flat-panel display  18  and the external CRT at the same time. 
     The flat-panel display  18  tends to be one of the most expensive components of the portable computer  10 . Yet, today many portables  10  become obsolete because various components, such as the processor, deliver lackluster performance relative to new computer systems. Therefore, it would be desirable to continue using the flat-panel display  18  even after that portable computer  10  has become obsolete, perhaps as the monitor of a desktop PC (assuming the desktop PC has a dual display adapter card). The problem is that today&#39;s portable computers  10  can only output video signals, but cannot receive video signals from an external source for display on the flat-panel  18 . 
     Accordingly, what is needed is a display controller architecture for portable computers that allows portable computers to display external video signals. The present invention addresses such a need. 
     SUMMARY OF INVENTION 
     The present invention provides a dual display mode portable computer. The portable computer includes a flat-panel display, and a display controller for outputting an internal video signal to the flat panel display. The portable computer further includes means for receiving an external video signal, and a multiplexer for outputting the internal video signal to the flat-panel display during a first display mode, and for outputting the external video signal to the flat-panel display during a second display mode, thereby enabling the portable computer to act as a display device for an external computer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating current display technology found in portable computers. 
         FIG. 2  is a block diagram illustrating the display controller architecture in accordance with one embodiment of the present invention. 
         FIG. 3  is a block diagram illustrating a display controller architecture in accordance with a second preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention relates to display controller architecture for portable computers. The following description is presented to enable one of ordinary skill in the art to make and use the invention and is provided in the context of a patent application and its requirements. Various modifications to the preferred embodiments and the generic principles and features described herein will be readily apparent to those skilled in the art. Thus, the present invention is not intended to be limited to the embodiments shown but is to be accorded the widest scope consistent with the principles and features described herein. 
     The present invention provides a display architecture for portable computers that allows portable computers to receive and display the output of a desktop PC or another portable computer. 
       FIG. 2  is a block diagram illustrating the display controller architecture in accordance with one embodiment of the present invention, where like components from  FIG. 1  have like reference numerals. According to the present invention, the portable computer  30  is provided with an extended mode display (XMD) that enables the portable computer  30  to operate dual display modes. In normal display mode, the portal computer  30  displays the internal video signal  16  on the flat-panel display  18 , while in XMD mode, the portable computer  30  receives and displays an external video signal  32  on the flat-panel display  18 . 
     In the first embodiment of the present invention, the display controller architecture includes a dual mode display connector  34 , a sensor  36 , an analog-to-digital (A/D) converter  38 , converter logic  40 , and a multiplexer  42 . In a preferred embodiment, the dual mode display connector  34  is a 15-pin RGB connector for coupling a video cable from an external PC or portable to the portable computer  30 . The external video signal  32  preferably comprises RGB analog input and timing signals. 
     When the external video signal  32  is received on the connector  34 , the A/D converter  38  converts the signal  32  into a digital signal. The converter logic  40  then maps the output of the A/D converter  38  into a format required by the flat panel display  18 . After the conversion, the formatted digital video signal is input into the multiplexer  42 . The multiplexer  42  has two inputs: the standard internal video signal  16  from the display controller  14 , and the external video signal  32  output from converter logic  40 . The multiplexer  42  outputs either the internal video signal  16  or the external video signal  32  to the flat-panel display  18  depending on the current display mode of the portable computer  30 . 
     In a preferred embodiment, controls are added to the portable computer BIOS that would enable the portable computer  30  to operate in the following modes:
         1) normal display mode—flat-panel only,   2) normal display mode—flat-panel and an external CRT (same image on both displays),   3) normal display mode—external CRT only, and   4) XMD mode—external signal displayed on external CRT and flat-panel.       

     In a preferred embodiment of the present invention, the display modes of the portable computer can be controlled in a variety of ways including automatic detection or by an explicit user command. The automatic mode requires the sensor  36  to automatically detect an external device coupled to the dual mode display connector  34  and driving the external video signal  32  through the connector  32  when the portable computer  30  is powered-on. This can be an extension of the power-on sequence of the portable computer  30 . Alternatively, if the portable computer  30  and the external computer are already powered-on and the two are connected, it is possible for both computers to detect each other. In this case, the user may be given an option to select a “hot plug” mode. In any event, once the sensor  36  detects the external video signal  32 , the portable computer  30  may be switched to XMD mode. 
     The second method for controlling the display modes of the portable computer  30  is through the use of a dual mode display software driver  34  that enable the user to manually invoke the XMD mode either by clicking on an icon or by a key sequence. In a preferred embodiment, the dual mode display driver  34  displays a dialog box at startup that allows the user to select automatic switching mode or manual switching mode. The driver  34  may also give the user an option to select the resolution of the external computer (e.g., VGA, XVGA, or SVGA) when it cannot automatically be detected. 
     The manual method for switching the display mode is preferable over the automatic detection method because the user can toggle the display between the primary flat-panel display  18  and the external PC. More specifically, the portable computer  30  remains on and fully booted even when the flat-panel  18  is used as the second display device of the external PC, and a hot key sequence is used to toggle flat-panel display  18 . 
     Once the display mode of the portable computer  30  is set, a control signal  36  is sent to the multiplexer  42  to control which video signal is sent to the flat-panel display  18 . If the portable computer  30  is in normal display mode, then the multiplexer  14  outputs the internal video signal  16  to the flat-panel display  18 . If, however, the portable computer  30  is in the XMD mode, the multiplexer  42  outputs the external video signal  32  to the flat-panel display  18 . A primary advantage of using the multiplexer-based display architecture is that multiplexer  42  eliminates the need for a custom graphics controller, and the display architecture can be implemented into current portable computer designs. 
     Referring now to  FIG. 3 , a display controller architecture is shown according to a second preferred embodiment of the present invention, where like components from  FIGS. 1 and 2  have like reference numerals. The second embodiment adds a dual mode display connector  52  to the existing external CRT connector  22  of the portable computer  50  that connects to the external CRT connector  22 , rather than adding a new connector to the portable computer. The CRT connector  22  is a female type connector. Therefore, the dual mode display connector  52  is a female to male type connector for accepting a display cord from another computer. The advantage of using the dual mode display connector  52  is that current portable computers do not have to be redesigned to accept a new input connector. 
     According to the second embodiment, a second multiplexer  54  is connected between the external CRT connector  22  and the D/A converter  20 . In normal display mode, the D/A converter  20  outputs the internal video signal that drives an external CRT to the external CRT connector  22 . In XMD mode, a control signal  56  is sent to the second multiplexer  54  to isolate the D/A converter  20  and to allow the external video signal  32  to enter the external CRT connector  22  through the dual mode display connector  52 . The external video signal  32  is then input to the A/D converter  38  and converter logic  40 , and output to the flat-panel display  18  through the multiplexer  42 , as described above. 
     A display architecture that provides portable computers with an extended mode display has been described. The present invention has been described in accordance with the embodiments shown, and one of ordinary skill in the art will readily recognize that there could be variations to the embodiments, and any variations would be within the spirit and scope of the present invention. Accordingly, many modifications may be made by one of ordinary skill in the art without departing from the spirit and scope of the appended claims.