Patent Publication Number: US-2005128164-A1

Title: Video driving module for multiple monitors and method for the same

Description:
FIELD OF THE INVENTION  
      The present invention relates to a video driving module for monitor and method for the same, and especially to a video driving module for multiple monitors and method for the same.  
     BACKGROUND OF THE INVENTION  
      Nowadays a computer operation system, such as Windows 98/ME/2000/XP, generally has the ability to use multiple monitors on one system. The system with multiple monitors can be advantageously used in an airport or train station to post schedules or in a stock market for a TV wall.  
       FIG. 1  shows a computer connected externally to a plurality of monitors in a prior art multiple monitor system. The motherboard of the computer  1  generally has a plurality of expansion slots such as PCI slots or ISA slots to allow for upgrades. To render the computer capable of using multiple monitors, the operation system of the computer should have an associated ability to drive multiple monitors. Moreover, a plurality of video adaptor cards  12  is installed in the slots of the motherboard and each of the video adaptor cards is connected to a monitor  2 . The operation system sends corresponding video signals through a chipset  11  on the motherboard to each of video adaptor cards  12  through a bus. The video signal will be displayed on corresponding monitor.  
       FIG. 2  shows a computer connected externally to a plurality of monitors in another prior art multiple monitor system. The number of accessible monitors in  FIG. 1  is limited by the number of slots in the motherboard. If the motherboard of a computer has 4-6 slots, the computer can only control 4-6 monitors. In the multiple monitor system shown in  FIG. 2 , the shortage is improved by providing a plurality of bus bridges  13  between the chipset  11  and the video adaptor cards  12 . Each of the bus bridges  13  can be connected to, for example, four video cards  12  and about 4-6 bus bridges  13  can be arranged on the motherboard. In other words, the computer according to  FIG. 2  can control up to 16-24 monitors through only one motherboard.  
       FIG. 3  shows the schematic view of a prior art video driving module  14  for display. The video driving module  14  is referred to as a video adaptor card inserted in a slot or a display chipset on the motherboard. The display chipset  14  has an interface unit  144  for receiving video data from a chipset, and a video memory  141  for storing the video data, a graphics engine  143  to provide a graphic acceleration function for reducing the load on the CPU, and a CRT controller  142  for processing the color of each pixel in the video data and generate a digital video signal to a digital to analog converter (DAC)  145 . The DAC  145  converts the digital video signal into a RGB analog signal and sends the RGB analog signal to a monitor  2 . Moreover, the CRT controller  142  sends vertical/horizontal sync signals to the monitor  2 . In  FIG. 3 , the CRT controller  142  is set to operate in a true color mode to encode each pixel by 24 bits.  
      The video driving module  14  shown  FIG. 3  is used for a conventional monitor. The video driving module  14  can only be connected to one monitor  2 . For a computer, the number of monitors accessible is doubled by doubling the CRT controller  142  and the DAC  145 . The architecture is shown in  FIG. 4 , in which the video driving module  14  has a first CRT controller  142   a  and a second CRT controller  142   b . If the techniques illustrated in  FIG. 2  and  FIG. 4  are simultaneously used in a system, the system can access up to 32-48 monitors.  
      The system with ability to use multiple monitors can adopt the architecture as shown in  FIGS. 1, 2 , and  4 . However, the operation system of the computer must initialize each video driving module  14  to refresh each monitor  2 . The reason is that the I/O ports of the video driving modules  14  and the addresses of the video memory  141  are identical for the chipset on motherboard.  
       FIG. 5  is a flowchart of describing the refreshing step of a video driving module with the assumption that i=1 at beginning and the refreshing number of monitor is 48. In a first step  51 , the access interface of video driving module  1  is opened. Then in step  52 , the video memory of video driving module  1  is refreshed. Afterward, in step  53 , the access interface of video driving module  1  is closed. Step  54  checks whether all video driving module are refreshed. If yes, the refreshing operation is finished, if not, i is added to 1 in step  55  and the procedure returns to step  51 . The total refreshing time is 24 sec if the refreshing time for one monitor is 0.5 sec.  
      The above mentioned prior art scheme for achieving multiple monitors has the following problems. A system with the architecture shown in  FIG. 1  is limited by the number of slots. A system with the architecture shown in  FIG. 2  is limited by the number of bus bridges  13  and the size of the motherboard. Moreover, the provision of the bus bridges also increases cost. A system with the architecture shown in  FIG. 4  has the problem of complicated circuits and a higher cost than that of  FIG. 3 , even thought two monitors  2  are driven by one video driving module. Moreover, the system with the architecture shown in  FIG. 4  can only refresh the monitors one by one, and cannot refresh all monitors simultaneously. The monitor is not refreshed until the corresponding path of the video driving module  14  is opened. The total refreshing time is considerable if the number of the monitors is large.  
     SUMMARY OF THE INVENTION  
      It is an object of the present invention to provide a video driving module for multiple monitors and a method for the same, wherein a single video driving module is used to drive multiple monitors.  
      It is another object of the present invention to provide a video driving module for multiple monitors and a method for the same, wherein a single video driving module is used to refresh multiple monitors.  
      To achieve the above objects, the present invention provides a video driving module for multiple monitors, which comprises a CRT controller, and a plurality of converters. The CRT controller generates an image signal and the image signal is divided into a plurality of equal parts, each of the parts being associated to one of the digital-to-analog converters.  
      To achieve the above objects, the present invention provides a motherboard for multiple monitors, which motherboard comprises a chipset for outputting a plurality of image signals, a CRT controller converting the plurality of image signals to a plurality of video signals, and a plurality of converters converting the video signals to signals adapted for the monitors and outputting the signals to monitors.  
      To achieve the above objects, the present invention provides a method for driving multiple monitors, a plurality of monitors being driven by a CRT controller and a plurality of converters, the method comprising following steps: the CRT controller processes a plurality of image signals into a plurality of video signals; the plurality of video signals is sent to the plurality of converters for converting the video signals into signals adapted for the monitors; and the signals adapted for the monitors are sent to the monitors. 
    
    
     BRIEF DESCRIPTION OF DRAWING  
      The various objects and advantages of the present invention will be more readily understood from the following detailed description when read in conjunction with the appended drawing, in which:  
       FIG. 1  shows a computer connected externally to a plurality of monitors in a prior art multiple monitor system;  
       FIG. 2  shows a computer connected externally to a plurality of monitors in another prior art multiple monitor system;  
       FIG. 3  shows the schematic view of a prior art video driving module for display;  
       FIG. 4  shows a schematic diagram of a video driving module for two monitors;  
       FIG. 5  is a flowchart of refreshing step of video driving module;  
       FIG. 6  shows a schematic diagram of a video driving module according to the present invention; and  FIG. 7  demonstrates a video signal being output to a plurality of monitors according to the present invention.  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       FIG. 6  shows a schematic diagram of a video driving module  62  according to the present invention. The video driving module  62  comprises a video memory  621 , a CRT controller  622  and a plurality of DAC  625 . The operation of each component is similar to that in  FIG. 3  and the description thereof is omitted here. The present invention is characterized by the output of the CRT controller  622  being connected to a plurality of DAC  625 , which is different from the illustrations of  FIGS. 3 and 4 , wherein the output of the CRT controller  142   a  is connected to only one DAC  145 .  
      For many applications of multiple-monitor systems such as posting a schedule in a train station or airport, the display color does not exceed  256  colors. More particularly, 2-4 colors are sufficient. For even colorful applications such as an indicator in a stock market, 20 colors suffice. Full color output such as the case shown in  FIG. 3  is not practical for those applications.  
      In the present embodiment, the digital video signal output by the CRT controller  622  is divided into a plurality of equal parts corresponding to the number of the monitors  7 . The video driving module  62  has DAC  625  with a number corresponding to the monitors  7 . The color number displayed by the monitor  7  depends on the bit number of each partition.  
      For example, if the digital video signal output by the CRT controller  622  has 24 bits for each pixel, the CRT controller  622  will divide the 24 bit data into four parts. Each of the parts has 6-bit color representation for defining a new digital video signal. The CRT controller  622  is connected to 4 DAC  625 , and each DAC  625  is connected to a monitor  7 . Therefore, each monitor  7  can display 64 colors. The CRT controller  622  simultaneously sends a vertical/horizontal sync signal to each monitor  7  and simultaneously sends four sets of digital video signals to the four monitors  7 . Therefore, all monitors can be simultaneously displayed and refreshed.  
      When four image screens are simultaneously display to synthesize a virtual desktop, four sets of video signals are output from a chipset  61 . The four sets of video signals are sent through a bus and then sent to the video memory  621  through an interface  624 . The graphics engine  623  provides a graphic acceleration function for the video signals. The CRT controller  622  processes the color of each pixel in the video signals to generate four digital video signals to corresponding DAC  625 . The DAC  625  converts the digital video signal into RGB analog signal and sends the RGB analog signal to a monitor  7 .  
       FIG. 7  demonstrates a video signal output to a plurality of monitors. In this example, each monitor  7  has resolution of 640×480 and a pixel A in the 100 th  row and the 100 th  column of the video memory  621  is used as an example. The video signal in pixel A is processed by the CRT controller  622  and converted into a digital video signal with bits D 0 -D 23 . The bits D 0 -D 5  of the pixel A are output to pixel A 1  of CRT  1  in the 100 th  row and the 100 th  column. The bits D 6 -D 11  of the pixel A are output to pixel A 2  of CRT  2  in the 100 th  row and the 100 th  column. The bits D 12 -D 17  of the pixel A are output to pixel A 3  of CRT  3  in the 100 th  row and the 100 th  column. The bits D 18 -D 23  of the pixel A are output to pixel A 4  of CRT  4  in the 100 th  row and the 100 th  column. In other words, the data bits for one pixel of the video memory  621  can be mapped to a plurality of image data in a plurality of monitors.  
      To sum up, the video driving module  62  according to the present invention is connected to a plurality of DAC  625  through the output of the CRT controller  622 , thus controlling a plurality of monitors  7  by only one video driving module  62 . Moreover, the plurality of digital video signals output from the CRT controller  622  share the same graphics engine  623  and the same video memory  621 . An application program can simultaneously refresh all monitors.  
      The video driving module  62  according to the present invention can be implemented on a video adaptor card or directly on a motherboard. In the former case, the video driving module  62  is inserted into a slot as shown in  FIG. 1 . Moreover, a plurality of bus bridges  13  can be arranged on a motherboard to increase the slot number and drive more monitors.  
      The video driving module according to the present invention has the following advantages:  
      (1) driving a plurality of monitors with a single video driving module;  
      (2) simultaneously refreshing a plurality of monitors with a single video driving module; and  
      (3) flexibly adjusting the number of accessible monitors by adjusting the display color.  
      Although the present invention has been described with reference to the preferred embodiment thereof, it will be understood that the invention is not limited to the details thereof. Various substitutions and modifications have suggested in the foregoing description, and other will occur to those of ordinary skill in the art. Therefore, all such substitutions and modifications are intended to be embraced within the scope of the invention as defined in the appended claims.