MULTIPLE BUFFER COMPUTER DISPLAY CONTROLLER APPARATUS

Abstract: Multiple buffers are employed in a display controller for a computer display system. A video RAM is utilized in the display controller to hold display data corresponding to graphics to be displayed on the computer display monitor. And a series of dynamic RAMs are employed in the display controller to hold display data corresponding to images to be displayed on the computer display monitor. A data mixer receives and mixes signals from the video RAM and one of the dynamic RAMs to form signals which are used to drive the display monitor. The signals provide graphics displayed at one resolution overlaid on images displayed at a different resolution on the monitor. A FIFO buffer and rectangle loader provide efficient loading of blocks of display data in the display controller buffers.

Description: MULTIPLE BUFFER COMPUTER DISPLAY CONTROLLER APPARATUS Background of the Invention Resolution of each screen view of a computer display system is a function of two components. One component is the computer software which is executed by the computer and which outputs signals for the screen view. The other component is the monitor or display unit itself which receives the screen view signals from the computer. Typically a display controller is used to hold screen view signals output from the computer and to reformat and transmit the signals in a timely manner to continually refresh the display unit screen. With the various software programs and monitors available today, different combinations of software, display controllers and display units are made. Where the software requires for its output a certain pixel resolution of the receiving screen (monitor) and the monitor has a larger pixel resolution, correction is needed. Additionally, it is often useful to be able to display very high resolution continuous tone images on a monitor, but such high resolution for displaying graphics on the same monitor is unnecessary. This is especially the case where a high resolution image display unit, for example a typical 19 inch screen of 2560 pixels by 2048 pixels, hence 200 DPI (dots per inch), and PC software, which typically requires a receiving screen pixel resolution of 75-100 DPI, are utilized together to display graphics (i.e. user editorial markings and text) overlays on grey scale or color images. Another problem involves the demands placed on the display controller. The memory in the display controller must not only continuously refresh the monitor screen but also must have sufficient bandwidth so that new data can be loaded into the memory quickly. One solution is to employ a video- random-access-memory (VRAM) in the display controller in a wide-word dual-ported configuration. The VRAM has a memory matrix for holding data (screen view signals) and a cooperating high speed serial interface which transfers a multiplicity of pixel data at a time and frees the memory for access while simultaneously transmitting screen view signals. The VRAMs however are expensive. Accordingly, there is a need for a computer display system that provides high resolution image display in an inexpensive, and diverse software and hardware compatible manner. Summary of the Invention The present invention provides computer display controller apparatus which overcomes the problems of prior art. The apparatus includes a display controller coupled to the digital processor of a computer system to receive therefrom display data corresponding to elements to be displayed at different respective resolutions. The display controller has a first memory for holding display data corresponding to elements to be displayed at a certain resolution and a second or additional memory for holding display data corresponding to elements to be displayed at other resolutions. The display controller transfers, along one channel to a data mixer, display data from the first memory, and transfers along a separate channel display data from the second memory. The data mixer combines the display data from the first and second, and additional memories to form signals for driving a display unit coupled to the display controller. Driving means drive the memories of the display controller such that each pixel of display data from one of the first and second memories at one resolution is replicated to fill several corresponding pixels of the display unit of a higher resolution. In turn, the data mixer signals drive the display unit to display, at one resolution, elements corresponding to the display data from the first memory simultaneously with elements corresponding to the display data from the second memory at a different spatial resolution. In a preferred embodiment, the first memory of the display controller is a video RAM for holding display data corresponding to graphics to be displayed on the display unit. The graphics include user generated markings and text. The second or additional memories of the display controller are a plurality of DRAMs (Dynamic Random Access Memories) for holding display data corresponding to images to be displayed on the display unit. The images usually are displayed at a higher resolution than the graphics, the images and graphics being displayed at the same time on the display unit with the graphics usually overlapping the images. To that end, the present invention provides display of elements corresponding to display data from one of the first and second memories of the display controller overlayed on elements corresponding to display data from the other memory. To accomplish this, the signals formed by the data mixer include signals indicating precedence of settings of display unit pixels for the overlaying elements over the settings of display unit pixels for elements corresponding to display data from the other memory. In accordance with another aspect of the present invention, the data mixer forms signals as a function of display data from one of the first and second memories of the display controller. In accordance with another feature of the present invention, a transfer buffer is connected between the digital processor and display controller to hold display data until times of retrace of the display unit. During times of retrace of the display unit, the transfer buffer transfers display data to the display controller. In a preferred embodiment, the transfer buffer is a first-in first-out buffer. In a preferred embodiment, a rectangle loader is connected between the digital processor and the display controller for providing indications of memory addresses for blocks of display data from the digital processor to the display controller. The rectangle loader enables transferring of display data from the transfer buffer to the display controller in either a page mode or on a static column cycle. Further, the display unit may be operated in either page mode or on a static column cycle with signals from the data mixer to display the elements. Brief Description of the Drawings The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Figure la is a schematic illustration of an image plane and a graphics plane in a display system of the present invention. Figure lb is a diagrammatic view showing correspondence between positions on the graphics plane, image plane and screen view of Figure la. Figure 2 is a block diagram of an embodiment of the present invention. Detailed Description of the Preferred Embodiment The present invention provides for the high resolution display of an image on a monitor or display unit 34 (Figure la) of a computer system simultaneously with the lower spatial resolution display of graphics on the monitor screen. This is accomplished by employing a high resolution image plane 38 separate from a lower resolution graphic plane 40 as illustrated in Figure la. The graphic plane 40 is expanded and logically positioned in front of the image plane 38 such that graphics are displayed overlayed on images in a screen view 36 of the display unit 34. By way of illustration and not limitation, the screen view 36 is typically about 2.5 k pixels by 2 k pixels. The image plane 38 is 2.5 k bits by 2 k bits by 8 bits deep to support 256 gray levels. The graphic plane 40 is 1.25 k bits by 1 k bits by 2 bits deep to support a typical 100 DPI. screen resolution. The bits of the image plane 38 have a one to one correspondence with the screen view 36 pixels, and the bits of the graphics plane 40 have a one to four correspondence with the screen view pixels as illustrated in Figure lb. Thus, the shaded bit of the image plane 38 in Figure lb denoted I(xl,yl) positionally corresponds to the screen view pixel indicated S(xl,yl). And in the graphics plane 40, the bit position labelled G(xl,yl) positionally corresponds to screen view pixels S(xl,yl), S(x2,yl), S(xl,y2) and S(x2,y2). The other bits of the image plane 38 and graphics plane 40 similarly corresponds to respective pixels of the screen view 36. Each screen view pixel is driven by signals formed of the combination of the corresponding image plane bit and graphics plane bit as follows. For example, for each position in the image plane 38, an 8 bit signal is provided. For each position in the graphics plan 40, a 2 bit signal is provided. The 8 bit and 2 bit signals of a corresponding screen view position are logically combined to provide an output value for driving the pixel of the screen view 36 position. The 8 bit image plane 38 signal and 2 bit graphics plane 40 signal are preferably combined according to the following table where I--..I- denotes the 8 bit signal of the image plane 38 and G Q , G- indicates the 2 bit signal from the graphics plane 40. Table I Image IN Graphics IN Output G l' G o I 7 -..I 0 0 0 0 (black) I 7 ...I Q 0 1 127 (grey) I-—I Q 1 0 I 7 ..I Q (transparent/ image) i 7 ...I Q 1 1 255 (white) 10 Thus, in the preferred embodiment, it is the 2 bit signal from the graphics plane 40 which determines the setting of screen view 36 pixels. If the 2-bit graphics plane 40 signal is 00 indicating a black bit positioned on the graphics plane 40, the 15 corresponding screen view pixel is set to 0 (black) . If the 2-bit graphics plane signal is 01 indicating a gray level at the bit position in the graphics plane 40, then an output signal for a gray level, for example 127, is used to drive the corresponding 20 screen view pixel. If the graphics plane 2-bit signal is 10 indicating a bit position of the graphics plane 40 which is to give precedence to the underlying image plane bit for that position, an output signal indicating the image plane bits I Q 25 through I ? for that position is used to drive the corresponding screen view pixel. If the graphics plane signal is a 11 indicating a white bit in the graphics plane 40 then a white output value, for example, gray level 255 is used to drive the corresponding screen view pixel. In this manner, each screen view pixel is set so that the graphics of the graphics plane 40 are displayed overlaying the image of image plane 38. The foregoing is incorporated in a display system embodying the present invention as illustrated in Figure 2. The computer display system 44 has a digital processor or host 10 which generates output to be displayed on monitor 34. Digital processor 10 may be a macrocomputer or a minicomputer or of the PC type. Monitor 34 is any video display or CRT common in the art, such as a MegaScann UHR-2007. Host 10 transmits display data on buses 48 and 50 to a multiple buffer display controller 46. The display data includes image data and graphics data. And buses 48, 50 are bidirectional as described later. Display controller 46 employs a plurality of image buffers 14 for holding display data which corresponds to images of an image plane 38 (Figures la, lb) . Display controller 46 also employs a graphics buffer 16 for holding display data corresponding to graphics of a graphics plane 40 (Figures la, lb) . Preferably, image buffers 14 are dynamic RAMs each with at least 5 megabytes of memory, such as a Motorola 514256 DRAM. And graphics buffer 16 is a video RAM with at least one byte of memory, such as a Toshiba 524256 VRAM. According to active scan line timing generator 26, 8-bit image signals (I....I-) are output from image buffers 14 and 2-bit graphics signals (G,G-) are output from the graphics buffer 16 and are multiplexed in data mixer 30. The clock rate of timing generator 26 is coordinated with word width of output from buffers 14, 16 to provide data mixer 30 with appropriate amounts of image data and graphics data at a time. Address generators 20, 22 of buffers 14, 16 respectively are used to provide the proper memory address source of the image and graphics signals being output at the clocking of timing generator 26. The address generator 22 is of the type capable of (i) repeating an address to replicate a pixel of a line on the same line such that two similar pixels are adjacent each other on the line and (ii) repeating addresses to replicate a line of pixels to create two identical adjacent rows of pixels. This provides the 1 to 4 correspondence between graphics data of graphics plane 40 as held in graphics buffer 16 and pixels of screen view 36. Each pixel G Q G. from the graphics buffer 16 is replicated to four pixels of the screen view. Preferably, address generators 20 and 22 are of the Xilinx XC3030 type. Active scan line timing generator 26 is, for example, a Signetics PL10H20V or a similar type. Data mixer 30 combines the 8-bit image signal (I 7 ..I_) from one image buffer 14 and 2-bit graphics signal (G., G Q ) from graphics buffer 16 which correspond to a common screen view pixel. Data ixer 30 accomplishes the combining by logic gates arranged to implement Table I described above. The resulting output signal from data mixer 30 is transferred to a display driver 32 coupled to data mixer 30. Display driver 32 employs a digital-to- analog converter to convert the data mixer output signal to a voltage signal for driving the corresponding pixel of screen view 36. In the preferred embodiment, data mixer 30 includes a programmable logic array, such as a Signetics PL10H20V, coupled to a shift register or similar memory such as a Booktree BT424. And display driver 32 is a Megascan serializer Ser-2007m or similar digital-to-analog converter. The foregoing procedure is performed for each pixel of screen view 36 such that display driver 32 and display unit 34 scans and updates each line (row) of pixels of the screen view to refresh the screen view 36. In the preferred embodiment, active scan line timing generator 26 clocks the buffers 14 and 16 of display controller 46 such that display data for driving the screen view 36 is output during active scan line times of display unit 34. During retrace time of display unit 34 (i.e. retrace between lines of pixels as well as from the last line of pixels back to the first line of pixels in screen view 36) , a data loading timing generator 28 enables the transfer of image data between host 10 and image buffers 14. This is accomplished as follows. During times of retrace, active scan line timing generator 26 disables the output of image and graphics data signals from the memories 14, 16 of display controller 46 and transmits a signal (mem_avlb) indicating availability of the display controller memories 14, 16 to data loading timing generator 28. That signal is logically ANDed with a signal (have_data) from a transfer buffer 12 which indicates that image data from either host 10 or an image buffer 14 is currently being held in the transfer buffer 12. For the case where the resulting signal indicates that the display driver 32 is currently in a state of retrace (i.e. it is currently retrace time) and that transfer buffer 12 is currently holding subject data, the data loading timing generator 28 enables transfer buffer 12 to transfer the subject data to the desired destination (i.e. either an image buffer 14 or host 10). Data loading timing generator 28 is preferably a Signetics PLS105 programmable logic array programmed to implement an AND gate and other logic. Other state machines which produce the transfer signal upon the receipt of the mem_avlb and have_data signals together are also suitable. In a preferred embodiment, transfer buffer 12 is a first-in first-out buffer of 1024 bytes of memory, and bus 48 is a bidirectional 32 bit wide bus. To that end, transfer buffer 12 transfers image data from host 10 to an image buffer 14 or vice versa during retrace times of display unit 34. This allows time saving transfer of image data between display and other host applications. Also, host 10 transmits display data corresponding to graphics to buffer 16 over bidirectional bus 50. Since buffer 16 is a VRAM, host 10 can get immediate access to buffer 16 the majority of the time. Host access address generator 24 provides host 10 with the address of the available memory space in buffer 16. And scan line timing generator 26 roem__avlb signal enables host 10 to transmit display data. For further efficiency in loading display data into image buffers 14 of display controller 46, the present invention employs rectangle loaders 18. There is a different rectangle loader 18 for each image buffer 14. To transfer a block of image data to an image buffer 14, host 10 provides an indication of the extent of the block of display data. Preferably, an indication of the upper left hand corner and lower right hand corner of the block of image data is used. Upon the clocking of data loading timing generator 28, rectangle loader 18 cooperates with buffer 12 to load the subject block of image data into a corresponding image buffer 14 in a static column cycle or page mode as known in the art. Briefly, these two modes allow, for each row address, a series of column addresses and column strobes to load the block of data into image buffer 14. In turn, this reduces the loading time where a row address does not have to be separately given for each column address. In a preferred embodiment, rectangle loaders 18 are Xilinx XC3030 address generators. Other address generators of a similar type are suitable. Also as is common in the art, the page mode or static column cycle manner of displaying a block of data on the monitor 34 may be employed by display driver 32. Thus, efficiency is provided in both loading of image data into image buffers 14 as well as displaying image data on monitor 34. While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. For example, the relative resolution between graphics plane 40 and image plane 38 and, hence, displayed graphics and images may be other than 1 to 4 described above for purposes of illustration and not limitation.

Claims: CLAIMS 1. Display apparatus for receiving from a digital processor display data corresponding to elements to be displayed at different resolutions and for displaying on a display unit the elements at respective different resolutions from the received display data, the apparatus comprising: a display controller coupled to the digital processor to receive display data and having a first memory for holding display data corresponding to elements to be displayed at a certain resolution and at least a second memory for holding display data corresponding to elements to be displayed at another resolution; means for driving the memories of the display controller such that each pixel of display data from the first memory is replicated to a group of display unit pixels, different pixels of display data being replicated to different groups of display unit pixels; and a data mixer coupled to the display controller to separately receive display data from the first and second memories, the data mixer combining the display data from the first and second memories to form signals for driving a display unit coupled thereto, such that elements corresponding to the display data from the first memory are displayed on the display unit at one resolution simultaneously with elements corresponding to the display data from the second memory being displayed at a different spatial resolution on the display unit. 2. Apparatus as claimed in Claim 1 wherein the data mixer forms signals to display elements corresponding to display data from one of the first and second memories of the display controller as a function of display data of one of the memories. 3. Apparatus as claimed in Claim 1 wherein: the data mixer combines display data from the first and second memories according to a predetermined precedence of an element corresponding to display data of one of the first and second memories to be displayed at a display unit pixel over an element corresponding to display data from the other memory to be displayed at the display unit pixel, such that an element corresponding to display data from one of the first and second memories is displayed overlayed on an element corresponding to display data from the other memory. 4. Apparatus as claimed in Claim 1 wherein the first memory is a video random access memory for holding display data corresponding to graphics, and the other memories of the display controller are respective dynamic random access memories for holding display data corresponding to images. 5. Apparatus as claimed in Claim 1 further comprising a first-in-first-out buffer connected between the digital processor and the display controller to hold display data until times of retrace of the display unit, the first-in-first-out buffer transferring display data to the display controller during times of retrace of the display unit. 6. Apparatus as claimed in Claim 5 further comprising a rectangle loader connected between the digital processor and the display controller for controlling addressing of blocks of display data from the digital processor to the display controller. 7. Apparatus as claimed in Claim 5 further comprising a rectangle loader connected between the digital processor and display controller for enabling one of page mode and static column cycle transferring of display data from the first-in first-out buffer to the display controller. 8. Apparatus as claimed in Claim 1 further comprising means for operating the display unit in one of page-mode and static-column cycle with signals from the data mixer to display the elements. 9. A method of displaying, at a same time, on a computer display unit elements of different respective resolution from display data output by a digital processor coupled to the display unit, the method comprising the steps of: providing a display controller having a first memory for holding display data corresponding to elements to be displayed at one resolution and at least a second memory for holding display data corresponding to elements to be displayed at another resolution; coupling the display controller to a digital processor to receive display data therefrom; driving the memories of the display controller such that each pixel of display data from the first memory is replicated to a group of display unit pixels, different pixels of display data being replicated to different groups of display unit pixels; receiving display data separately from the first and second memories in a data mixer; and combining in the data mixer the display data from the first and second memories to form signals for driving a display unit coupled to the data mixer, such that elements corresponding to the display data from the first memory are displayed on the display unit at one resolution simultaneously with elements corresponding to the display data from the second memory being displayed at a different spatial resolution on the display unit. 10. A method as claimed in Claim 9 wherein the step of providing a display controller includes providing a display controller having a video RAM for a first memory and a plurality of dynamic RAMs for other memories, the video RAM for holding display data corresponding to graphics and the dynamic RAMS for holding display data corresponding to images. 11. A method as claimed in Claim 9 wherein the step of coupling the display controller to the digital processor includes connecting a buffer between the digital processor and display controller to hold display data until times of retrace of the display unit, the buffer transferring display data to the display controller during time of retrace of the display unit. 12. A method as claimed in Claim 11 wherein the step of connecting a buffer between the display controller and digital processor includes providing a rectangle loader coupled between the display controller and digital processor for enabling one of page mode and static column cycle transferring of display data from the buffer to the display controller. 13. A method as claimed in Claim 9 wherein the step of coupling the display controller to the digital processor includes providing a rectangle loader coupled between the digital processor and display controller for controlling addressing of blocks of display data from the digital processor to the display controller. 14. A method as claimed in Claim 9 further comprising the step of driving the display unit in one of page mode and static column cycle with signals from the data mixer to display the elements. 15. Display apparatus for receiving from a digital processor display data corresponding to elements to be displayed at respective different resolutions and for displaying the elements at respective different resolutions on a display unit from the received data, the apparatus comprising: a digital processor; a display controller for receiving display data from the digital processor, the display controller having a video RAM for holding display data corresponding to graphics to be displayed at one resolution on a display unit, and a plurality of dynamic RAMs for holding display data corresponding to images to be displayed at another resolution on the display unit; a buffer connected between the digital processor and display controller to hold display data from the digital processor until times of retrace of the display unit, the buffer transferring display data to the display controller during times of retrace of the display unit; means for driving the memories of the display controller such that each pixel of display data from the video RAM is replicated to a group of display unit pixels, different pixels of display data being replicated to different groups of display unit pixels; and a data mixer coupled to the display controller to separately receive display data from the memories of the display controller, the data mixer combining the display data from • *-' the video RAM and one dynamic RAM to form signals for driving the display unit coupled to the data mixer, such that elements corresponding to the display data from the video RAM are displayed on the display unit at 0 one resolution.simultaneously with elements corresponding to the display data from one dynamic RAM being displayed at a different spatial resolution on the display unit. 5 16. Display apparatus as claimed in Claim 15 further comprising a rectangle loader connected between the digital processor and the display controller for controlling addressing of blocks of display data from the digital processor. 0 17. Display apparatus as claimed in Claim 15 further comprising a rectangle loader connected between the digital processor and the display controller for for enabling one of page mode and static column cycle transferring of 5 display data from the buffer to the display controller. 18. Display apparatus as claimed in Claim 15 wherein the buffer connected between the digital processor and display controller is a 0 first-in first-out buffer.

Inventors: TAAFFE JAMES L, TAAFFE, JAMES, L.
Applicants: GEN HOSPITAL CORP, THE GENERAL HOSPITAL CORPORATION
Application year: 1991
Main classification: G09G1
IPC codes: G06T1, G09G5