Abstract:
Control of LCD backlighting, contrast, and video port selection with BIOS. Calls made from application programs to BIOS result in BIOS read and write operations to a distributed register in video adapters. The use of the register allows BIOS to simultaneously obtain information from multiple displays, as well as simultaneously execute hardware functions such as backlight control. In addition, use of BIOS simplifies programming of hardware related tasks such as backlight control to improve mean time between failure (MTBF) of LCD displays.

Description:
This is a continuation of application Ser. No. 07/902,414 filed on Jun. 19, 1992, now abandoned which is a continuation of appliction Ser. No. 07/525,510 filed on May 18, 1990, now abandoned. 
    
    
     CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is related to the commonly owned copending application entitled &#34;Apparatus and Method for Distributing Registers Across Multiple Adapter Cards&#34; filed May 18, 1990, bearing U.S. Ser. No. 7/525,509 now abandoned and naming Jeffrey D. Harper, Paul W. Kalendra, William J. Piazza, Howard C. Tanner, and Anh Vinh, one of whom is the inventor named herein, the contents of which is specifically incorporated by reference herein in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     This invention relates to BIOS interfaces. In particular, a BIOS interface for controlling video features of a system. 
     2. Background Art 
     A Liquid Crystal Display (LCD) is a commonly used peripheral (I/O) device on computer systems. Due to the nature of the LCD hardware, it is important to have the contrast and backlight properly adjusted to enable a user to read the LCD display screen comfortably. However, in commercial settings terminals may be unattended for long periods of time. This is disadvantageous because the useful life of the display is a function of backlight use. For example, the mean time between failure (MTBF) of the LCD screen is greater than that of a CRT display, but the MTBF of the backlight is less than that of a CRT display. Therefore, the ability to control usage of the backlight directly effects the relative reliability of an LCD display in relation to a CRT display. In turn, this effects the decision of a purchaser when reliability is an issue. It would be desirable to have a simple way to automatically control the backlight with software to avoid unnecessary wear on the backlight. 
     In addition, in systems with multiple displays, switching from one display to another involves a complicated software process. Typically a prior art system will have to do the following to switch displays: 
     1. Save the BIOS interrupt vectors and BIOS data areas of the currently selected video port. 
     2. Change hardware registers to deselect one port and select another. 
     3. Restore the interrupt vectors and BIOS data area of the newly selected video port. 
     In summary, the reliability of LCD terminals is not as good as the hardware will allow. In addition, control of display switching is inefficient. The prior art has not shown the ability to easily and efficiently control LCD hardware displays. 
     SUMMARY OF THE INVENTION 
     An object of this invention is to switch between a plurality of video ports within a system through a single BIOS call. 
     Another object of this invention is to control the LCD backlight of the currently selected video port. 
     A further object of this invention is to turn off the LCD backlight after a predetermined amount of time. 
     Yet another object of this invention is to control the LCD contrast voltage of the currently selected video port. 
     A still further object of this invention is to have the system set a pre-stored default contrast automatically whenever the system is restarted. 
     An additional object of this invention is to program applications such that they can easily manipulate LCD display hardware functions. 
     The foregoing and other objects, features and advantages of this invention are achieved by controlling the LCD switching, backlight, and other functions, such as contrast, through a single BIOS call. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows the distributed register format. 
     FIG. 2 is a diagram showing the elements of the system in relation to the distributed register. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     For the purposes of this disclosure, the following definitions will be used: 
     1. BIOS - Basic Input Output Subsystem - a set of assembly 
     language programs residing in EPROM on the system board or option adapter cards. BIOS provides an interface between hardware functions and the operating system and application programs. 
     2. POST - Power On Self Test - a set of assembly language programs residing in EPROM on the system board or option adapter cards. POST routines execute whenever the system is turned on or restarted and they verify the proper operation of the hardware and initialize devices as required. 
     3. BIOS Data Area - an area of RAM memory used by BIOS to store the status of various devices which it controls. On IBM PC compatible machines, the BIOS data area consists of the 256 bytes of memory starting at absolute address 400h. 
     4. Extended BIOS Data Area - an extension to the BIOS Data Area. The Extended BIOS Data Area starts out as the top 1K bytes of memory in IBM PC Compatibles and can be expanded if necessary. A large portion of this data area is dynamically allocated to whatever installed device needs it and is quite frequently unused. 
     5. NMI - Non Maskable Interrupt - an interrupt which cannot be disabled using the standard methods of masking interrupts (i.e., the CLI instruction or by changing the Interrupt Mask Register in the interrupt controller chip.) 
     6. BBSRAM - Battery Backed Static RAM - a special area of memory which is nonvolatile because it is kept powered by a battery when the system power supply is off. 
     By way of general overview, control of LCD backlight and contrast can be accomplished with a single BIOS call. In addition, switching between LCD displays in a system with multiple displays can also be accomplished with a single BIOS call. The advantages of this invention is that the controlling software is more efficient, therefore having better performance. In addition, the functions such as backlight control are easier to implement in software, which results in a greater probability that they will be used to increase LCD display MTBF. 
     The same backlight and contrast BIOS calls work on all video ports regardless of whether the controlling hardware resides on the system board or a single or multiport video adapter. The backlights can be forced to turn themselves off after a preset time interval (this is important for extending the useful life of the backlights). They can be turned back on and reset to turn off automatically again with a single BIOS call. 
     The distributed register, described in the cross-referenced application, is used by the instant invention. FIG. 1 shows the format of the distributed register as used in the preferred embodiment. FIG. 2 shows the distributed register in relation to the other elements of the system. 
     The following is an overview of how each of the major functional enhancements to the video subsystem were implemented: 
     1. Contrast control, backlight control, and display sensing. Contrast and backlight control registers and display sense registers are located at different addresses for the video ports available within the system. BIOS will make a determination as to which video port is currently selected and automatically select the proper registers to use. This simplifies the calling procedure. 
     2. Backlight &#34;auto-off&#34; function. Application software can specify that the backlights should turn off automatically after a certain period of time so that the life of the backlights will be prolonged by not using it during periods of inactivity. The application can then make calls to the `backlight on` function of BIOS whenever system activity requiring the backlight is detected. This call will turn the backlight on if it is off and will reset the timeout if the backlight is already on. 
     The implementation of the `auto-off` feature is as follows: 
     (a) A COUNTER and TIMEOUT VALUE are stored in the Extended BIOS Data Area for each of the 5 video ports. If the COUNTER and TIMEOUT VALUE are set to 0, the auto-off feature is not being used. 
     (b) To start the auto-off feature, an application makes a BIOS call that sets the TIMEOUT VALUE to a non-zero value and performs the `backlight on` function. 
     (c) Whenever the `backlight on` BIOS call is made, BIOS turns the backlight on and copies the TIMEOUT VALUE to the COUNTER. 
     (d) The COUNTER is decremented by the NMI handler once every 10 milliseconds. When the COUNTER reaches 0, the backlight is turned off. 
     (e) To stop the auto-off feature, an application makes a BIOS call that sets the TIMEOUT VALUE to 0. 
     3. Default contrast setting. During power on, POST will retrieve a default contrast setting from the Battery Backed Static RAM (BBSRAM) if BBSRAM has been initialized. If BBSRAM has not been initialized, a value stored in the EPROM is used. A utility program under the &#34;setup&#34; portion of the diagnostics allows the user to set the default value into BBSRAM. 
     4. Video switching. Video switching begins during POST. Five data areas of slightly less than 64 bytes each are allocated in the Extended BIOS data area. Four data areas are provided for adapter ports and one data area is provided for a video port on the system board. As each video port is tested and initialized, POST saves certain key interrupt vectors and portions of the BIOS data area by copying them into the Extended BIOS Data Area before initializing the next video port. For example, the system board video is enabled and initialized, then the vectors and BIOS data are saved in the Extended BIOS Data Area before moving on to initialize the I/O channel video adapters. Each of the 5 video ports in the system has its own buffer in the Extended BIOS Data Area. Whenever an application program requests switching to a different video port, BIOS takes the following actions automatically: 
     (a) Interrupt vectors and BIOS Data Area parameters related to video are copied to the Extended BIOS Data Area in a block reserved specifically for the currently selected video port. 
     (b) Hardware registers are changed to cause the deselection of one port and the selection of another. 
     (c) Interrupt vectors and BIOS Data Area parameters related to video are copied from the BIOS Data Area (from the block reserved specifically for the newly selected video port). 
     A specific implementation of the preferred embodiment is shown in the following detailed description of the BIOS functions (the use of BIOS and BIOS functions are well known in the art) used to implement this invention: 
     The following gives the details of portions of the BIOS interface under INT 15h (System Services) which have been created to access the extensions described in this herein. 
     
         ______________________________________INT 15H (SYSTEM SERVICES)AH=OD0H TERMINAL SPECIFIC FEATURESAL=03H EXTERNAL CRT SENSEON RETURN:AL = STATUS:   BITS 7-2 = 0   BITS 1-0 = EXT CRT SENSE BITS    ECS  BITS    1    0       MEAN    1    1       LCD (NO EXT CRT)    1    0       31KHZ COLOR DISPLAY    0    1       31KHZ MONOCHROME                 DISPLAY    0    0       15KHZ COLOR CRTNOTE:      THIS CALL ALWAYS WORKS WITH      THE CURRENTLY      SELECTED VIDEO PORT.AL=05H LCD DISPLAY CONTRAST AND BACKLIGHTCONTROLBH=00H     SET OPERATOR DISPLAY CONTRAST      LEVEL TO BL      O&lt;= BL &lt;= OF)      (SETTING BL TO ZERO TURNS THE      VOLTAGE TO THE IICD PANEL OFF)NOTE:      THIS CALL ALWAYS WORKS WITH      THE CURRENTLY      SELECTED VIDEO PORT.BH=01H     ASSIGN `CONTRAST UP`      FUNCTION TO KEY BLBH=02H     ASSIGN `CONTRAST DOWN`      FUNCTION TO KEY BL (WHEN      ENABLED, THE CORRESPONDING      KEY ON THE KEYBOARD      IS USED TO      INCREASE OR DECREASE      THE OPERATOR      DISPLAY CONTRAST.      THE KEY MAY NOT      BE USED FOR ANY OTHER PURPOSE      AND WILL NOT RESULT IN A SCAN      CODE BEING PASSED TO      THE APPLICATION. BOTH      UP AND DOWN FUNCTIONS      DO NOT HAVE TO BE      ASSIGNED SINCE THE KEYS      CONTRAST VALUES WILL      `WRAP`. TO DISABLE      THIS FEATURE, SELECT KEY      00 FOR BOTH FUNCTIONS,      WHICH IS THE DEFAULT.)BH=03H     OPERATOR DISPLAY BACKLIGHTNOTE:      THESE CALLS ALWAYS WORK      WITH THE CURRENTLY      SELECTED VIDEO PORT.BL=00H       BACKLIGHT OFFBL=01H       BACKLIGHT ONBL=02H       BACKLIGHT ON, AUTO-OFF        IN CX SECONDS        IF CX=0000, AUTO-OFF        FUNCTION IS DISABLED        AND THE BACKLIGHT        WILL REMAIN ON.BL=03H       STATUS        ON RETURN:        AL=BACKLIGHT STATUS        BITS 7-2 = 0        BIT 1 = 1 IF BACKLIGHT        IS IN AUTO-OFF        MODE (CX WILL RETURN        TIMEOUT VALUE IN SECONDS)        BIT 0 = 1 IF BACKLIGHT        IS CURRENTLY ONNOTES:     1)    WHEN OPERATING IN            AUTO-OFF MODE,            THE &#34;ON&#34;            COMMAND WILL TURN THE            DISPLAY ON AND            RESTART THE TIMER.            THE DISPLAY WILL THEN            TURN OFF AGAIN AFTER            THE SPECIFIED TIME            INTERVAL UNLESS A KEY            IS PRESSED ON THE            MEMBRANE KEYBOARD.      2)    TO COMPLETELY DISABLE            THE AUTO-OFF            FUNCTION AND ALLOW            SIMPLE CONTROL USING            THE ON AND OFF COMMANDS,            CALL AUTO OFF            (Bl=02H) WITH CX SET            TO 0. (THIS TURNS            THE DISPLAY ON AND            CANCELS AUTO-OFF) THEN            USE THE NORMAL OFF CALL.      3     WHEN IN AUTO-OFF MODE,            THE BACKLIGHT WILL            TURN ON (IF IT IS OFF)            WHEN A KEY IS            PRESSED ON THE KEYBOARD            AND THE KEYSTROKE            WILL BE THROWN AWAY.      4)    ON TOUCHSCREEN UNITS,            TOUCHSCREEN ACTIVITY            WILL NOT TURN THE            BACKLIGHT BACK ON.            TOUCHSCREEN DEVICE DRIVERS            OR APPLICATION            PROGRAMS HANDLING            TOUCHSCREENS SHOULD            INCLUDE A CALL TO TURN            THE BACKLIGHT ON            WHENEVER TOUCHSCREEN            ACTIVITY IS DETECTED.AL=0AH VIDEO PORT SELECTIONBH= 00H SELECT VIDEO PORTBL=00H PORT 0 (SYSTEM BOARD)BL=01H PORT 1 (ADAPTER)BL=02H PORT 2 (ADAPTER)BL=03H PORT 3 (ADAPTER)BL=04H PORT 4 (ADAPTER)ON RETURN:ZF=1         MEANS REQUESTED PORT        DOES NOT EXIST (THE        HARDWARE REGISTERS WILL        STILL BE SET TO        SELECT THE NON-        EXISTENT PORT)ZF=0         MEANS REQUESTED PORT EXISTS(IF THE MOST SIGNIFICANT BIT OF BLIS SET WHEN THIS CALL IS MADE, THESPECIFIED VIDEO PORT WILL BESELECTED AND IT WILL ALSO BE RESET TOBIOS VIDEO MODE 3 USING A BIOS INT 10HAX=0003H CALL.) THIS CALL CHANGESALLOWS THE SELECTION OF ANY VIDEOPORT (WHETHER IT IS ON THE SYSTEMBOARD OR THE SINGLE OR MULTIPORTVGA CARD) BY PERFORMING THEFOLLOWING FUNCTIONS:    1)  BIOS DATA AREAS AND        INTERRUPT VECTORS FOR        THE CURRENTLY SELECTED        VIDEO PORT ARE        SAVED IN THE EXTENDED        BIOS DATA AREA (A        UNIQUE AREA FOR EACH        VIDEO PORT)    2)  HARDWARE REGISTERS ARE        CHANGED TO SELECT        THE REQUESTED VIDEO PORT    3)  BIOS DATA AREAS AND        INTERRUPT VECTORS        ASSOCIATED WITH THE        NEWLY SELECTED VIDEO        PORT ARE RESTORED FROM        THE EXTENDED BIOS        DATA AREABH=01H     RESERVED FOR POST/BIOS      (SAVE PORT DATA AREA)BH=02H     RESERVED FOR POST/BIOS      (RESTORE PORT DATA AREA)BH=03H     QUERY CURRENT VIDEO      PORT RETURNS CURRENTLY      SELECTED VIDEO PORT NUMBER      IN AL (O TO 4).On return from all AH=0D0H calls:All registers preserved except AX (unless otherwisenoted)If AH=86 and CY=1, invalid functionor subfunction was given______________________________________