Classifications

• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
  • G06K15/00—Arrangements for producing a permanent visual presentation of the output data, e.g. computer output printers
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
  • G06K2215/00—Arrangements for producing a permanent visual presentation of the output data
  • G06K2215/0002—Handling the output data
  • G06K2215/0062—Handling the output data combining generic and host data, e.g. filling a raster
  • G06K2215/0065—Page or partial page composition

Definitions

• the present invention relates to the field of page printing systems, and specifically to image processors for page printing systems.
• Page printing systems are well-known and utilize many different types of printers. For example, electrically actuated mechanical print wheels, xerographic drums, and laser printers are all commonly used to form page printing systems.
• a printed page is formed by printing discrete picture elements (pixels) at fixed physical locations on an output medium such as paper.
• the picture elements have different intensities or color such as black and white.
• the printing device is a matrix printer
• the printed page is defined by a matrix of small locations which register either a black or white pixel.
• each pixel is a square measuring 1/240 inch on a side. Each pixel is much smaller than the smallest character or
• each character or shape is formed by a number of pixels.
• the printer operates by scanning the output media along one of its two axes at a constant speed.
• the paper moves parallel to a direction P called the "pageward” direction.
• the laser beam scans in a direction S called the “scanward” direction.
• the scanward direction is orthogonal to the pageward direction.
• the laser beam is turned on and off at each pixel location thereby forming either black or white pixels as the laser beam scans across the page.
• a full line in the scanward direction is called a scanline.
• a full page of scanlines results in the printed page.
• the data which represents the -printed page and which is supplied to the printer is stored in a computer memory and is called a "page image" or page image data.
• the page image is stored in the memory locations of a computer or other storage device.
• pixels are black or white
• one bit can be stored in one memory cell.
• Each bit of the digital representation which constitutes a page image must have a correspondence to a pixel in the printed page both as to pixel intensity (black or white) and location.
• the printed page is represented as a sequence of 2640 vectors, each vector composed of 2040 pixels.
• the page image can be stored
• OMPI in 2640 memory sections with each section having 2040 cells.
• Each memory cell stores one bit of information with the value "0" denoting a white pixel and the value "1" denoting a black pixel.
• Each memory section corresponds to one scanline (vector) of the printed page and hence there is a one for one bit to pixel map from bits in the memory cells of memory to pixels on a printed page.
• An alternative representation for a page image is achieved by using run-length encoding of sequences of pixels of the same intensity.
• scanlines are represented as sequences, each sequence being defined of the form (length) (color) , where length denotes the number of bits or pixels and "color” is either " " for white, or "B” for black.
• length denotes the number of bits or pixels
• color is either " " for white, or "B” for black.
• digital encoded representations which can be used to represent page. images.
• a "page layout” is a high-level encoded representation of an entire printed page.
• a page layout is encoded using a page layout language.
• the page layout language employs a library or table of basic shapes called "glyphs". Glyphs include letters, numbers, symbols and characters or shapes of all types and sizes. Additionally, the page layout language encompasses instructions which define where glyphs are to be located on a printed page.
• a page layout expressed in a page layout language is decoded to form page image data which correlates pixels to locations on a printed page.
• An image processor is a device which accepts the high-level encoded page layout data stored in digital form and process the page layout to form decoded page image data, also in digital form. The page image data is then transmitted to the printer to cause the printer to form the printed page.
• Image processors for high-speed printers are faced with a number of limitations. High-speed printers normally perform their printing function at a uniform rate. In prior art devices, image processors have processed the encoded page layout data to generate the decoded page image data at a rate which can match the constant data rate required by the printer. If the image processor is too slow in generating the page image data, then an incorrect page will be printed since the printers normally do not permit the stopping of the printing of a page at any point between the beginning and the end.
• Prior art image processors have been designed for uniform rate printers.
• One type of prior art image processor requires that the page image for the entire printed page be processed and stored in a full-page buffer before the printing operation commences.
• a full-page buffer system there is no problem ensuring that the page image will be available when the page image information is required by the printer.
• Such full-page buffer systems do have the problem of greater hardware cost and complexity.
• such full-page buffer systems have an inter-page delay problem when multiple printed pages are to be printed in rapid succession. The inter-page delay results from
• the inter-page delay causes the overall printing speed for many printed pages to be greatly reduced. Accordingly, it is desirable to avoid the inter-page delay for high-speed printing.
• alternating buffers In order to increase the speed of processing, other prior art image processors have employed alternating buffers.
• the page layout information is processed to fill one buffer with digital representations constituting a first part of the page image. After the first buffer is filled with a part of the page image, that first buffer is emptied to the printer for printing the printed page. While the first buffer is being emptied to the printer, the second buffer is being filled by processing of the page layout to form the next portion of a page image. After the first buffer is emptied and the second buffer is filled, the roles of the two buffers are exchanged. The second buffer is emptied to the printer while the first buffer is again filled. The process continues of alternately filling and emptying the buffers. In this manner, the inter-page delay is avoided or reduced provided the buffer fill rate equals the buffer empty rate.
• the image processor may produce the page image at a rate slower than the rate at which the printer prints. In prior art devices of the type described, the slower rate results in an error in the printed page.
• the present invention is a page printing system in which highly-encoded page layout information is processed to form a printed page.
• An image processor processes the page layout information to form decoded page image data.
• the image processor operates to form
• a printer operating at a preestablished printing rate prints the printed page, during a printing time.
• the printer forms a scanned array of variable intensity pixels in response to the page image data.
• the variable rate of the image processor is determined such that the duration of the processing time does not exceed the duration of the printing time.
• a printer interface connects the image processor to the printer so that the page image data determines the intensity (black or white) of the printed pixels which form the printed page.
• the image processor generates the decoded page image data and stores the data in a dynamic window buffer.
• the rate of filling the window buffer is a function of the rate at which the image processor processes the page layout information.
• the rate at which the window buffer is emptied, to supply page image data to the printing device is determined by the rate of printing of the printing device. Accordingly, the rate at which the dynamic window buffer is filled is variable and different from the rate at which the buffer is emptied.
• the rate of filling the dynamic window buffer at times can be less than the rate at which the dynamic window buffer is emptied; provided that, at other times the rate at which the dynamic window buffer is filled is greater than the rate at which it is emptied.
• the only . requirement is that the printing duration, occurring to empty the buffer, cannot exceed the processing duration, occurring to fill the buffer, for any period of time which will cause the window buffer to be empty and the printer to be without information to print.
• the capacity of the dynamic window buffer is less than the capacity required for a full printed page. Accordingly, the dynamic window buffer scrolls through the page image, in the pageward direction, so that the page image data stored in memory cells at any given point in time is less than the amount of data required for a full printed page. Because the window buffer size can be made small, the image processor of the present invention is economical.
• the present invention is able to process page layouts which are locally complex and which require long processing times.
• the local complexity slows down the rate at which the page image data fills the dynamic window buffer.
• the slower rate may be less than the rate at which the printer forms the printed page, provided that, at other times, the image processor can fill the dynamic window buffer at a compensatingly greater rate than the rate at which the printed page is formed.
• the size of the dynamic window buffer is selected to accommodate the maximum local complexity of the page layout. Typically, the number of scanlines in the window buffer is greater than four times the maximum character height to be processed.
• the dynamic buffer window size is measured in terms of the number of scanlines of data that may be stored. For a typical printed page with a laser printer scanned by 2640 lines, a typical dynamic buffer size is 64 scanlines. With a dynamic window buffer of this size, up to 64 scanlines are processed and stored in the
• the window buffer is emptied on a first-in, first-out basis. If the window buffer is emptied at a rate which is greater than the rate at which the window buffer is being filled, fewer than 64 scanlines of data will be available in the buffer.
• the fullness of the buffer is indicated by a top scanline .
• indicator (Paint Top) which indicates the current scanline being filled.
• the top scanline of the window buffer (Window Top) and the bottom scanline (Window Bottom) are recorded and changed as processing progresses.
• the difference between Window Top and Paint Top within the window buffer is the number of scanlines occupied with data to be transferred to the printer. If the Window Top equals the Paint Top before the printed page is printed, . then an error in the printed page will have occurred since the image processor fill rate has failed to keep up with the printer print rate.
• the size of the dynamic window buffer is selected so as to avoid situations where the window buffer is emptied of valid data before the complete page image is printed.
• the present invention achieves the objective of providing an economical page printing system and an improved page printing system which greatly facilitates the handling of local complexity in the generation of page images and the printing of printed pages.
• Fig. 1 depicts an overall block diagram of a page printing system including an image processor and a printer.
• Fig. 2 depicts a printed page field which is printed by the printer of the Fig. 1 system.
• Fig. 3 is a block diagram representation of the image generator within the image processor of the Fig. 1 system.
• Fig. 4 is an electrical schematic representation of the printer interface which forms part of the image processor of Fig. 2.
• Fig. 5 is a representation of an expanded view of a portion of the printed page of Fig. 2.
• a host computer connects to an image processor 3 which in turn connects to a printing device 4.
• the host computer 2 specifies a page to be printed using an encoded page layout.
• the image processor 3 receives the page layout information over the bus 5 and processes the page layout to form a page image which is digitally stored by the image processor.
• the image processor 3 provides over the bus 6 page image data
• The. printing device 4 is typically any well-known laser printer. Such a device will move a sheet of paper, for example, of standard size such as 8.5 x 11 inches, along a pageward axis while scanning a laser beam orthogonally thereto along a scanward axis.
• the paper will typically be advanced in the pageward direction at the rate of 565 scanlines per second.
• the laser will scan along the scanward axis with a scanward rate of 1.84 x 10 pixels per second.
• the laser printer will typically have a retrace time between the end of one scanline and the beginning of
• the bus 6 normally receives information serially by bit in the form of a stream of digital l's and 0's.
• bit rate on the bus 6 once a scanline starts, must provide a new bit every 544 x 10 — 9 second. The printer will
• a laser printer which has these typical characteristics is manufactured and sold by Canon, model LBP-10.
• a printed page field 11 of the same size as the paper 10 in the printing device 4 of Fig. 1 is shown.
• the printed page 11 is represented by 2640 scanlines 0, 1, ...» 2639 along the P-axis direction.
• each scanline of the printed page 11 is represented by 2040 pixels designated by the pixel locations 0, 1, 2, ..., 2039 in the S-axis direction. Accordingly, the entire printed page 11 is represented by 5.3856 x 10 pixels.
• OMPI pixel is either white or black depending upon the page image data supplied by the image processor 3 of Fig..1.
• the printed page 11 consists entirely * of white pixels except within region 12.
• the region 12 is located with its upper left-most corner commencing at the 1,000th pixel location in the S-axis ' direction and at the 500th scanline location in the P-axis direction of the printed page 11.
• Fig. 5 Further details of the printed page region 1? are shown in Fig. 5.
• the upper left-hand corner along the P-axis starts with the scanline 500. Only a portion of scanline 500 is shown in the S-axis direction running from pixel 1,000 through pixel 1023.
• the printed page portion 12 includes three glyphs including "H” 63, "i” 64 which are two normal alphabet characters. Additionally within the region 12, underscore graphic representation " " is designated glyph 65.
• the printed page of Fig. 2, including the printed page portion 12 of Fig. 5, is specified by the host computer 2, or any other convenient device, using a page layout language.
• the page layout language is encoded and is transferred to the image processor 3 of Fig. 1.
• the image processor of Fig. 1 functions to process the encoded page layout information to form page image data.
• the page image data, from the image processor 3 of Fig. 1, is transferred, a bit at a time, to the printer 4 of Fig. 1 to cause the printer to print the printed page of Fig. 2 including the printed page portion 12 of Fig. 5.
• all of the area within the glyphs 63, 64 and 65 will be black pixels while all of the rest of the area in Fig. 5 and Fig, 2 will be white pixels.
• the glyph 63 In Fig. 5, the glyph 63, the character "H", is 15 scanlines high as measured in the P-axis direction and 9 pixels wide as measured in the S-axis direction. Since, in the example being described, each pixel is 1/240 inch, the glyph 63 in Fig. 5 has a dimension of 0.0625 inch high by 0.0375 inch wide. This size is roughly the size of characters from standard typewriters or printers.
• the image processor 3 is comprised of an image generator 7 and a printer interface 8.
• the image generator 7 connects to the host computer 2 by means of the bus 5 and connects to the printer interface 8 via a bus 9.
• bus '9 is defined to be the well known Multibus commonly used for interconnecting microprocessors.
• the printer interface 8 in turn connects via the bus 6 to the printer 4.
• the image processor 3 of Fig. 1 processes the high-level encoded page layout information from the host computer 2 in a process which is called "painting."
• the painting forms and stores the page image data which is in turn transferred over the Multibus 9 to the printer interface 8 a scanline at a time.
• the printer' interface 8 transfers the data from the interface over the bus 6 a bit at a time to the printer 4.
• the transfer rate over the bus 6 must be at a rate which matches the rate of operation of the printer 4.
• the printer 4 requires a constant rate of data on the bus 6 since the paper 10, once printing has
• OMPI started, is moved at a constant rate. If data is not available on bus 6 at a rate which matches the required rate of printer 4, an error in printing will occur. -
• the rate at which the painting process in image generator 7 occurs is asynchronous with respect to the rate at which data is transferred out over bus 6. Accordingly, the image generator 7 is capable of painting at a high rate when the page layout from the host computer 2 is not complex. In a similar manner, the image generator 7 paints at a slow rate whenever the page layout is complex. The image generator 7 therefore can average the slow painting rates and the fast painting rates provided that the overall average painting process does not leave the printer interface without valid page image data to be transferred over the bus 6 when required by the printer 4.
• the image generator 7 which is part of the image processor 3 of Fig. 1, is shown in greater detail.
• the image generator 7 includes any well-known processor 15.
• processor 15 is a Motorola 68000.
• Processor 15 connects to a memory 16 via an internal bus 17.
• Processor 15 and bus 17 also connect to a universal asynchronous receiver/. transmitter (UART) 14.
• UART 14 connects bus 17 to the bus 5 for communication between the image generator 7 and the host computer 2 of Fig. 1.
• the processor 15 also connects to an interface 18 which in turn connects to the Multibus 9.
• the interface 18 is a standard device for connecting the bus 9 to processors, such as processor 15.
• the interface " 18 also connects to the internal bus 17 for communication between bus 17 and the bus 9.
• Memory 16 includes a page layout buffer 16-1, a dynamic window buffer 16-2, a glyph table 16-3, a program section 16-4 and a utility section 16-5.
• the sizes of these different sections of memory are selected to ensure that they have adequate room for the various tables and information which they store as will be apparent from the description which follows. In the example described, a 128K word memory, organized in 16-bit words, is adequate.
• the image generator 7 is downloaded with information from the host computer 2. While down- r loading is a convenient way of loading the information into the memory 16, the memory 16 can be loaded in any conventional way and does not require the use of a host computer. For example, the information can be keyed in from a keyboard, transferred from a word processor, or obtained from any other convenient source.
• Page layout information is loaded into the page layout buffer, memory section 16-2.
• a glyph table is loaded into the memory section 16-3.
• the glyph table defines a mask for each of the characters that can be painted by the image generator.
• Control programs and other routines are loaded into the memory section 16-4.
• the memory section 16-5 is for any ordinary utility functions which are used by processor 15.
• the dynamic window buffer, memory section 16-2 is the section of memory 16 in which the results of the painting operation are stored.
• section 16-2 stores 64 scanlines of page image data with 128 16-bit words per scanline in approx ⁇ imately 8K words of memory.
• the operation of the image generator 7 after being downloaded from the host computer 2, is to fetch the page layout commands from the buffer 16-1 process the commands to form and to store the page image data within the dynamic window buffer 16-2.
• references to character glyphs in the page layout commands causes a table look-up to access a character mask from the glyph table of section 16-3.
• the mask for the glyph from table 16-3 is overlaid at the appropriate location in the dynamic window buffer 16-2 under the control of the processor 15. Accordingly, the "painting" process occurs when the dynamic window buffer 16-2 is loaded by the decoding and processing of page layout information from the layout buffer 16-1.
• the dynamic window buffer 16-2 is emptied under control of the processor 15 through the interface 18 to the bus 9. From the bus 9, the page image data is loaded into the printer interface of Fig. 4.
• the printer interface 8 of Fig. 1 is shown in further detail.
• the printer interface 8 is connected to the bus 9 from the image generator of Fig. 3.
• the bus 9 is shown in further detail to include the control lines 48, the 16-bit MDATA bus 49, and the 20-bit MADDR bus 50.
• the printer interface of Fig. 4 accepts the page image data, on data bus 49, and stores it in the scanline buffer 21 through a receiver 47 and a data register 20.
• the data in the scanline buffer 21 represents the portion of the page image data required to specify a full scanline of pixels (2040 pixels) for a printed page as indicated, for example, in the printed page of Fig. 2.
• the page image data from the buffer 21 is selected by the multiplexer 22 to be transferred a bit at a time through the flip-flop 23 and the driver 24 to the video control lines (IVID) 28.
• Lines 28 connect as a part of the bus 6 to the printer 4.
• the "1" or "0" bit on the lines 28 determines the black or white, respectively, pixel which is printed by the printer 4.
• the MDATA(00-15) bus 49 connects to the receiver (RCVR) 47.
• Receiver 47 is a standard device which is energized to connect the bus 49, when enabled by the control line IMASEL, to the 16-bit bus 61.
• the 16-bit bus 61 is connected as an input to the 16-bit data register 20.
• the data on bus 61 is stored in register 20 under control of the LOAD DATA signal on line 58 from the address decoder 52.
• the bus 61 has its 11 lowest-order bits connected to the address counter 32 which is loaded under control of the LOAD ADR signal on line 57 from the address decoder 52.
• the four lowest-order bits of address are loaded into the. pixel counter (PIXCTR) 35 and the seven higher-order address bits are loaded into the WORD counter (CTR) 33.
• control information is loaded from the bus 49 into the control register 54 under control of the WRCTRL signal on line 56 from the address decoder 52.
• the control register 54 includes the register location for the IPRINT signal which, when set to 1, commands the printer of Fig. 1 to commence, a printing operation.
• the IPRINT signal is connected to the printer of Fig. 1 on line 70 which is part of the bus 6 in Fig. 1.
• the status information from the status register (STAT REG) 53 is gated onto the MDATA bus 49 under control of the READ STAT signal on line 55 from the address decoder 52.
• the status register 53 records the ITOP and the IPRINT END signals received on lines 71 of bus 6 from the printer 4 of Fig. 1.
• the decoding of the signals by decoder 52 is under control of a device decoder 59.
• the device decoder 59 decodes logical "l's" for the M(16-19) bits from the address bus 50 to enable the output line 51.
• the address decoder 52 accepts the bits M(0,1) from the bus 50 and decodes them to enable one of the lines 55, 56, 57 or 58.
• the receiver 47 is enabled to transfer any of the information on bus 49 through to the bus 61.
• the address counter 32 includes the word counter 33 and the pixel counter 35.
• the word counter 33 addresses through its 7-bit output X(04-10) any one of 128 words stored in the scanline buffer 21.
• Buffer 21 is, in the particular example being described, a random access memory of 128 x 16 bits.
• the buffer 21 has the 16-bit word from the data register 20 loaded into the buffer 21 at the address specified by the word counter 33 whenever the LOAD DATA line 58 from the address decoder 52 is enabled. When the LOAD DATA line 58 is not enabled, then the data at the word location specified by the word counter 33 appears output from the buffer 21 on bus 25 as an input to the multiplexer 22.
• the multiplexer 22 performs a 16 to one demultiplexing of the word output from the buffer 21 under control of the 4-bit output from the pixel counter 35.
• the signal output (BUF OUT) on line 26 from the multiplexer 22 connects as the D input to the flip-flop 23.
• the 1 or 0 data value of the BUF OUT line 26 is clocked into the flip flop '23 by the BIT CLK signal on line 43.
• the data value stored in flip flop 23 connects from the Q output on line 27 (VID LAT) as an input to the driver 24.
• the driver 24 converts the single signal line VID LAT to the dual-line 28 signal I VID.
• the I VID signal turns the laser beam on for a black pixel or off for a white pixel during the printing operation hereinafter described.
• the address counter 32 is counted by the BIT CLK signal on iine 43 from the divide-by-10- circuit 36.
• the divide-by-10 circuit 36 divides the clock signal from the 18.43 MHz clock 37 to provide the BIT CLK signal at a 1.843 MHz frequency.
• the BIT CLK on line 43 only appears when the circuit 36 is enabled
• the flip flop 38 has a "1" clocked to its Q-output by the START LINE signal on line 40 from the receiver- 39.
• the D input to the flip flop 38 is wired to a logical "1".
• the receiver 39 receives the dual-line 40 IBD signal from the printer 4 of Fig. 1 to signal that the printer requires the data to be sent for a scanline.
• the START LINE clocks the flip-flop 38 which in turn enables the VID GO signal on line 42 causing the BIT CLK signal to be generated on line 43 to start the address counter 32 counting.
• the address counter 32 Prior to this time, the address counter 32 has been loaded with all zeros so the address counter, in the present embodiment, always starts at the zero address and counts 2048 counts representing each of the pixels in a scanline.
• the pixels are stored in buffer 21 in 128 words, 16-bits per word, where each bit represents one pixel.
• the 16-bits (pixels) represented by each word are addressed in order one at a time by the stepping of the pixel counter 35 from its all zero condition through 16 counts which cause a carry-out on line 44.
• the carry-out on line 44 through the OR gate 34, counts the word counter 33 to the next word count.
• the multiplexer 42 selects the 16-bits output from the buffer 21 one at a time in the manner previously described.
• the MAX CT signal is clocked to provide a "1" on the Q output on flip-flop 45 to energize the LINE DONE signal on line 46.
• the LINE DONE signal resets the flip-flop 38, disabling the VID GO signal and preventing any further
• the purpose of the LINE DONE signal on the control line 48 is to signal the image generator of
• Multibus 9 to the scanline buffer 21 in preparation for the next scanline of data which is to be printed by the printer 4 of Fig. 1.
• GRAPHIC RULE 2 P-pos S-pos Height Width
• P-pos scanline location in the pageward direction between 0 and 2639
• S-pos pixel location in scanward direc ⁇ tion between 0 and 2039
• Width dimension in pixels in the scan ⁇ ward direction
• commands of three different classes are shown, namely, TEXT, -GRAPHIC and CONTROL.
• Each command comprises up to 5, 16-bit words of data denominated as Word-0, Word-1, . . . Word-4.
• the contents for each of the words within a command are specified in the columns under FORMAT in TABLE 1.
• the command CHAR (identified- by a Word-0 equal to 1) is a typical example of TEXT commands.
• RULE (with Word-0 equal to 2 ) belongs in the GRAPHIC command class.
• the command END (with Word-0 equal to 3) is a CONTROL command.
• the Word-1 stores a
• P-pos 16-bit primary designation
• S-pos 16-bit representation
• S-pos 16-bit representation
• CHAR ID character identification code
• the Word-3 stores a Height representation which is a 16-bit representation of the height of the graphic glyph
• Word-4 stores a 16-bit representation Width, which designates the width of the graphic glyph.
• the CHAR ID can also include a font number in addition to the ASCII code. In the present example, however, only a single font is employed and therefore the font number can be ignored.
• the page layout data is down loaded from the host computer 2 into the page layout buffer 16-1 of Fig. 3.
• the page layout buffer 16-1 in Fig. 3 includes two portions, an unsorted page layout buffer and a sorted page layout buffer.
• the starting address of the unsorted page layout buffer is given as UB and the starting address of the sorted page layout buffer is given as SB.
• the unsorted page layout for the Fig. 5 representation appears in the following- TABLE 2.
• the page layout buffer of TABLE 2 includes four commands, two CHAR commands commencing at the address UB+0 and UB+9.
• the table includes a RULE command beginning at address UB+4 and an END command beginning at UB+D.
• the Word-0 location at address ⁇ B+0 specifies that it is a character.
• the Word-3 location at address UB+3 specifies the ASCII code for "H". Referring to Fig. 5, that "H” has its starting position, the upper left-hand most corner at scanline 503 and with pixel address 1003. These values appear in the address locations UB+1 and UB+2 of TABLE 2. Accordingly, the first four addresses in the unsorted page layout buffer, that is addresses UB+0 through UB+3, specifies that the character "H" is to be painted starting at the location in the P-axis 503 and in the S-axis 1003.
• next five word addresses namely, UB+4 through UB+8, specify that a RULE command for the glyph 65 of Fig. 5 is present.
• the glyph 65 is to start at the P-axis scanline 524 and at the S-axis pixel address 1002.
• the height of the glyph is to be 3 scanlines and the width in the S-axis direction is to be 18 pixels.
• the unsorted page layout data of TABLE 2 is sorted, using a standard sorting routine based on the contents of Word-1, for each of the glyphs in the unsorted buffer. The results of that sorting appears as the sorted page layout data and is shown in the following TABLE 3.
• SB Starting address of Sorted Page Layout Buffer in image generator memory
• the starting address of the sorted page layout buffer is SB. With this reordering, the sorted page layout buffer is ready to be used by the processor 15 Fig. 3 to paint the page image into the dynamic window buffer 16-2.
• the sorted page buffer of TABLE 3 is accessed in the order of SB+0 to the end at SB+D.
• a glyph table During the processing of the CHAR commands on TABLE 3, the details concerning each character must be obtained from a library called a glyph table. In order to be able to address the glyph, however, the glyph starting address must be accessed from a glyph address pointer table.
• the glyph address pointer table is shown in the following TABLE 4.
• GA is starting address of GLYPH
• ADDRESS POINTER TABLE in image gener ⁇ ator memory
• a pointer address for addressing the pointer table is the ASCII code specified in the CHAR ID from Word-3 of the CHAR command. That code (48 (HEX) in the case of the character “H” and 69 (HEX) for "i”) is added to the starting address, GA of the glyph address pointer table and the contents of the resulting address yields the desired glyph address.
• the glyph starting address for the character "H” is Kl.
• the starting address for the character "i” is the address K2.
• the starting address for those characters is obtained from the TABLE 4 pointer table. After the starting address has been obtained, the proper addressing of the glyph table can be made.
• the glyph table entries for the characters H H" and "i” are shown in the following TABLE 5.
• the first word for a glyph entry specifies its height, which for the "H” is 15 scanlines and for the "i" is 14 scanlines,
• the second word specifies the width, which for the "H” is 9 pixels and for the
• Fig. 5 we can compare the aspect of the sample characters with their entries in the glyph table. It is apparent that the height of the character “H” is 15 scanlines in that it extends from scanline 503 to scanline 517. Similarly, the height of the character “i” is 14 scanlines and it extends from scanline 504 to scanline 517.
• the character “H” extends from pixel address 1003 to pixel address 1011.
• the black pixels extend from S-axis address 1015 through 1017.
• the CHAR command at address UB+9 in TABLE 2 specified the S-axis location 1014 so that the white pixel in scanline 504 and S-axis location 1014 together with the black pixels in S-axis locations 1015, 1016 and 1017 define the first hexadecimal digit for the character "i” (the character 0111 represents a hexadecimal 7) . All of the characters after 0111 for the character "i” are zeros so that the remainder of the hexadecimal representation for the first scanline for the character "i” is 000 and the full representation is 7000 as shown in TABLE 5.
• the starting address for the character "H” in Fig. 5 is the S-axis location 1003.
• the first four bits, from 1003 through 1006 are 1110 which correspond to a HEX E. Accordingly, E is the first HEX character in the first scanline of "H” of TABLE 5.
• the second digit for the first scanline of the character "H” from the S-axis addresses 1007 through 1010 is the binary 0011 which is a 3 HEX.
• the next four bits of the character "H" are 1000 running from the pixel S-axis address 1011 through 1014 is
• O PI binary 1000 which converts to 8 "HEX.
• the final digit for the character "H” is binary 0000 which is 0 (HEX) .
• the data for the first scanline of "H” is E380 (HEX) as shown in TABLE 5.
• all of the other data representations for each of the scanlines for each of the characters appear in the glyph table of TABLE 5.
• Width store one scanline [ (Window Width + 15) "div” 16]
• R16 PixVal Pixel Value register Stores pixel value in its rightmost bit
• the dynamic window buffer is a section of random access memory, or other storage which stores a predetermined number of scanlines of data. That number is set forth as the Window Height, which is
• the Window Height is equal to approximately four times the height of the largest character to be printed.
• the Window Height is equal to 64.
• the Window Width in the present example is set equal to 2040 pixels which can be stored in 128 16-bit words per scanline.
• the printer 4 of Fig. 1 requires that sufficient information be entered into the dynamic window buffer before the paper is started in order to ensure that the page image data will be available in sufficient time for printing pixels on the paper.
• the number of scanlines required to be processed before the printer is commanded to start is 32.
• the process page routine which is executed to paint the dynamic window buffer relies on a number of operations. Specifically, those operations are as follows:
• the first sequence is to initialize the various factors as previously described, the Window Width register is set to 2040 in 1.1.1.
• the Window Width register is set to 2040 in 1.1.1.
• - X O PI Word Width register is set to 128 in 1.1.2.
• the Window Height is set to 64 in 1.1.3.
• the Start Printer Delay, the Printer Started, and the Top Reached registers are set to 32, 0 then 0, respectively.
• the clear window sequence is entered.
• the purpose of this sequence is to ensure that the contents of the dynamic window buffer are set to represent a blank portion of a page.
• the sequence 2.1 is to clear the window buffer by resetting all bits in all words to a logical "0" starting with the Window Base and extending through the entire dynamic buffer window.
• the Window Base is the starting address of the dynamic window buffer 16-2 in the memory 16 of Fig. 3. Every word within the window buffer is accessed and set to logical "0" in the step 2.1.1.
• the Window Top register is set to "0".
• step 2.3 the Window Bottom register is set equal to the Window Height - 1, which is 64 - 1 or 63. Accordingly, at this point, the dynamic window buffer is the 64 scanlines which correspond to scanlines 0 through 63 in the P-axis direction of the printed page of Fig. 2.
• the paint loop sequence is entered and- the pointer to the current sorted buffer address, PSB, is set equal to the base address SB, starting address of the sorted page layout buffer.
• the Paint Top register is set to Word (SBH) which is the scanline index corresponding to the topmost character in the page which is 503. After this the Paint Loop Sequence is entered by jumping to 3.6.
• the Paint Top was set to 503 in step 3.2.1 while the Window Top is still at 0 as set in step 2.2. Hence, the Paint Top is greater than or equal to the Start Printer Delay, which was set equal to 32 in step 1.2.1.
• the CTL register 54 in Fig. 4 is set so that the IPRINT signal equals 1 and the Printer Started register in the image generator 7 of Fig. 3 is set equal to 1.
• word (PSB) (this is the first entry of TABLE 3) , is examined to see if it is a character command, CHAR, which it is.
• the Paint Top register is set to word (PSB+1) , which is the data in SB+1.
• the S-pos register is set to word (PSB + 2), which is the data from the address SB + 2 in TABLE 3.
• the CHAR-ID register is set word (PSB+3) , which is at the address SB + 3 in TABLE 3.
• the pointer to the glyph table PGT is set equal to the address of the glyph entry for "H", which is Kl.
• step 4.3 the Width register is set to the contents of the word at PGT + 1 location, which is the Kl + 01 address in the TABLE 5.
• the data from the glyph table from the TABLE 5 at this location is 0009 (HEX) indicating that the width of the character is 9 pixels.
• step 4. 4 the processing waits until the contents of the Window Bottom register, storing 63 at this time, minus the Paint Top register, storing 503 at this time, is greater than or equal to the contents of the Height register which was set to 15 in the step 4.2. Where this condition is satisfied, which occurs after the printer has printed 455 scanliens, and thus the
• Step 4.5 defines a loop which will be carried out for a scanline address, SM, from (SM) equal to 0 to (SM) equal to 14.
• the loop of step 4.5 assures that each scanline required for the character, the character "H" in the present example, will be accessed from the glyph table.
• the sequence 4.5.1 is nested within the sequence of 4.5 and operates for every pixel address, TM, from (TM) equal to 0 to (TM) equal to 8.
• the step 4.5.1 assures that the full pixel width of the character, 9 pixels in the present example of an "H" will be accounted for.
• the steps 4.5.1.1 and following are executed.
• the X register is set equal to the contents of the S-pos register, which in accordance with step 3.2.2 was set equal to 03EB (HEX) , which is the S-axis position 1003 at which the character "H" in Fig. 5 is to commence.
• step 7.1 the WPTR register, which is a pointer to the glyph .mask is set.
• the PGT + 2 portion is the initial address of the glyph mask (of TABLE 5) , which for the current operation is Kl + 02.
• step 7.2 the PixPal register takes word (WPTR), which is the data E380 (HEX) from the Kl + 02 address of the glyph table. This data is left shifted by the amount of the PM, which in the present example is 0 modulus 16. Accordingly, there is no left shift.
• WPTR the data E380 (HEX) from the Kl + 02 address of the glyph table. This data is left shifted by the amount of the PM, which in the present example is 0 modulus 16. Accordingly, there is no left shift.
• the "and" function logically AND's the number 8000 (X).
• the binary value of this number has a 1 in the left-most bit position and all the remainder of the bits are 0.
• this number is AND'ed with the other number in the 7.2, it has the effect of setting only the left-most bit as the single value for storing in the PixVal register. That value will be either a logical "0" or "1".
• the 7.3 step returns to the 4.5.1.3 step which then is followed by the 4.5.1.4 step, which calls step 8, the Set Window Pixel Subroutine.
• step 8.1 the word pointer register WPTR is set to point to the correct word within the dynamic window.
• the pointer WPTR is set equal to the Window Base plus the displacement of the beginning of the scanline Y from the beginning of the window, plus the displacement of the word that stores pixel X within the scanline Y.
• Window Base is the starting address of the dynamic window buffer of the memory section.16-2 of Fig. 3.
• Scanline Y is stored in the dynamic window at
• step 8.1 sets WPTR equal to (Window Base + 7102).
• This result is the word location in the dynamic window buffer that stores the first bit of the character "H” and at a location which corresponds to the S-axis location 1003 and the P-axis location 503. Having found the address of that location in the window buffer, as done in step 8.1, step 8.2 sets the contents of that location as pointed to by the pointer WPTR, equal to the contents of what already existed in that location as logically OR'ed with the logical "1" or "0" determined in step 7.2.
• step 8.2 the PixVal before the logical OR'ing is shifted from its left-hand-most position within a word to its correct position within the word, which in the case of the first bit of the character "H” is an 11-bit shift. This 11-bit shift is determined by the 1003 modulus 16 arithmentic which equals 11.
• the step 8.2 then OR's the logical "1" bit in the 11th bit position of the word at WPTR. At this point, a first bit of the page image data for the character "H" has been loaded into the dynamic buffer window at a location which will ultimately result in the pixel being printed at the location S-axis 1003 and the P-axis position 503 of Fig. 5.
• the next step is 3.2.5 where the pointer to the sorted buffer, PSB, is set equal to the old value of PSB + 4.
• the step 3.2.5 steps the PSB address to the next location in the sorted page layout buffer which is TABLE 3. Since there were four words in the sorted page layout buffer for the CHAR command just processed incrementing by 4 is done in step 3.2.5, setting the pointer PSB at the beginning address for the next command in the sorted page layout buffer.
• the PSB register points to the sorted buffer at the SB + 8 address of TABLE 3. Since the command is not a CHAR command, then the processing jumps to 3.3. The RULE command is recognized so that the processing continues with 3.3.1.
• the various registers are loaded with the data from the sorted page layout buffer of TABLE 3, and in 3.3.5, the program goes to the Paint Rule Subroutine, which is step 5 of TABLE 7.
• the Paint Rule Subroutine is processed in a manner similar to the Paint Character Subroutine. After the underscore glyph has been painted, the processing returns in step 5.3 to step 3.3.5.
• the next step is 3.3.6 in which the sorted page layout buffer pointer, PSB, is incremented by 5. ⁇ Referring to the sorted buffer table, TABLE 3, the next command at
• step 3.3.7 causes the processing to go to 3.5 and from there to 3.2. Since the next command is END, the processing steps from 3.2 to 3.3 and 3.4. In step 3.4, the END command is detected and the process ⁇ ing goes to 6, the Terminate Sequence.
• step 6.1 the processing waits until the Window Top is greater than or equal to the Paper Height. At this point, nothing in the process page routine of TABLE 7 increments the Window Top. This incrementing occurs by the TRANSFER PROCESS ROUTINE described hereinafter in connection with TABLE 8.
• the register 54 in Fig. 4 transmitted to the printer 4 of Fig. 1, the IPRINT signal-.
• the printer sees the IPRINT signal equal to 1, it starts a print cycle.
• the print cycle starts the printer moving, and when the top edge, that is the first edge, of the paper reaches a prespecified point, the printer sends out a signal ITOP as a logical "1" which is loaded into the
• OMPI status register 53 which is regularly loaded by the processor 15 of Fig. 3.
• the printer regularly sends an IBD signal on line 40 of Fig. 4 (part of the bus 6 in Fig. 1) to signal the request for the IVID pixel data on line 28.
• the IBD signal starts the pixel transfer (that will be described in more detail below) to the printer. When no page is being printed, this transfer has no effect.
• the transfer finishes the MAX CT 31 signal clocks the LINE DONE 46 signal, whihc is transmitted to the interrupt circuit of the processor 15.
• the processor 15 immediately interrupts the processing which is currently going on and executes an interrupt routine which is the transfer process routine of TABLE 8.
• step 1 of the transfer process the first step is to save the status of the interrupted process, usually the process of TABLE 7, so that after the transfer process of TABLE 8, the processor 15' can continue processing at exactly the step that it was in before.
• the next step is 2 and the routine examines whether or not the Top Reached register is equal to 1.
• Top Reached has not been set equal to 1
• the routine in TABLE 8 goes to 3.
• the status register 53 of Fig. 4 is examined to see if ITOP is equal to 0. If so, then the routine of TABLE 8 goes to 6, loads the address counter 32 of Fig. 4 with all 0's and m step 7 restores status and resumes the interrupted process.
• the printer has been started (by the Process Page Routine of table 7) , eventually the paper top is reached, at which time the printer signals ITOP 71 f which causes the routine to go from 3.1 to 3.2.
• the Top Reached register is set equal to 1.
• control register 54 is reset so that IPRINT is "0", so that the next page will not be started until it is requested by the Process Page Routine.
• step 4 if the Window Top equals the Paint Top, then an error has occurred and the routine of TABLE 8 exits through step 6 and 7. Assuming that an error has not occurred, a transfer occurs in step b .
• step 5.1 the address counter 32 of Fig. 4 is loaded to all 0's
• step 5.2 the pointer within the scanline to be transferred, SPTR, identifies the word in the buffer memory to be transferred over the data bus 49 to the scanline buffer 21.
• the word address, SPTR for each word in the Window Top scanline is stepped from the starting word to the ending word.
• step 5.2.1 each of the words specified by the SPTR address determined in 5.2 is loaded into the data register 20 in Fig.4.
• 5.2.2 after the word is loaded, and 5.2.1, the contents of that word in the buffer memory are set to 0, thereby clearing the buffer in readiness for the next painting operation.
• the dynamic buffer window is advanced.
• step 5.3.1 the contents of the Window Top register are incremented by 1.
• step 5.3.2 the contents of the Window Bottom register are incremented by 1.
• step 6 the address counter 32 of Fig. 4 is loaded with all O's to put it in the starting condition for addressing the next scanline.
• step 7 the status is restored in the processor 15 and the process previously interrupted is resumed at the same point in the processing.
• the Window Top scanline is transferred from its location in the dynamic window buffer 16-2 over the image generator of Fig. 3.
• the effect of transferring out the Window Top scanline is to make that scanline available for new data to be painted by the painting process described in connection with TABLE 7.
• the Window Top scanline effectively become the bottom scanline in the dynamic window buffer.
• the rate at which each new Window Top scanline is transferred from the window buffer 16-2 to the scanline buffer 21 of Fig. 4 is fixed by the operation of the printer 4.
• the printer 4 at regular fixed intervals sends the IBD signal requesting a new scanline, thereby empyting the scanline buffer 21.
• the scanline buffer 21 is refilled by the transfer process routine of TABLE 8.
• the word counter 33 is initially set to 0 in the step 5.1 each time a new LOAD DATA signal is decoded by the address decoder 52, the word counter 33 is incremented to a new word address until all 128 words have been loaded into the buffer 21.
• the amount of time it takes to fill the scanline buffer 21 with the Window Top scanline from the dynamic window buffer is less than the amount of time taken for the retrace cycle of the printer 4 of Fig. 1.
• the amount of time it takes to load the scanline buffer 21 is less than 15 percent of the time that the printer takes in a single scanline cycle. For this reason, the time spent in the transfer process routine of TABLE 8 does not interfere with the processors ability to do the painting routine of TABLE 7. Most of the time of the processor 15 is spent in filling the dynamic window.
• the processing done in accordance with the TABLE 7 routine is asynchronous with respect to the processing done with the TABLE 8 transfer process routine.
• the rate of filling the dynamic window is a function of the local complexity of the data in the sorted page layout buffer. When that data is complex, the data filling the dynamic window slows
• the emptying of the dynamic window is a fixed rate as determined by the laser printer.
• the rate of filling the buffer for scanlines 503 through 517 and 524 through 526 is much slower than the rate of filling the lines 518 through 523, which required no time. Accordingly, the average time for filling the scanlines 503 through 526 inclusive is faster, because no time was spent on the lines 528 through 533.
• the problems presented by local complexity are significantly reduced because of the ability of this system to paint at a variable rate.
• the slow rate of filling the buffer is averaged with a fast rate of filling the buffer so that the average rate without causing errors in the printed page is effectively much higher.
• a direct memory access (DMA) circuit may be connected between the processor 15 and the memory 16 -so that certain memory accesses such as required to clear the dynamic window buffer, can be carried on in parallel with other processing by the processor 15.
• DMA direct memory access
• the dynamic window buffer has been described having a one-for-one map between bits in a cell and pixels on a printed page. While the amount of time required to paint the dynamic window buffer is not great when only white pixels are called for, the dynamic window buffer still has a space occupied when a one-for-one bit-to-pixel map exists.
• encoding schemes can be employed so that the data is stored more compactly. For example, run length encoding could be employed within the dynamic window buffer as one compaction technique. If page image data is compacted with an encoding scheme, a given physical size for the dynamic window buffer creates an effective dynamic window buffer of a larger size. For example, referring to Fig.
• the entire printed page can be represented within the dynamic window buffer of only 64 lines.
• the dynamic window buffer of only 64 lines.
• 64 scanlines worth of data even they are all white pixels, can appear in the dynamic window buffer at any one time.
• no time is required in filling the buffer, there is time required in emptying the buffer.
• no more than the equivalent of 64 lines can be stored into the dynamic window buffer. For this reason, the averaging of the high rate of painting when the local complexity is low with the slow rate of painting when the local complexity is high, is limited to a 64 scanline area.
• encoding is employed
• the average can occur over a much larger effective dynamic window buffer, even when the physical size of the dynamic window buffer is not increased.
• the painting process of TABLE 7 was carried on a bit at a time.
• a bite or word processing can be carried out.
• the Paint Character and the Paint Rule procedures will be modified to account for the multi-bit processing of page image data.
• an appropriate decoding of the encoded information can be included within the printer interface of Fig. 4.
• the output from the data register 20 would be connected through a decoder before entry into the scanline buffer 21.
• an encoded representation from data register 20 would be further decoded into the scanline buffer 21.
• the size of the scanline buffer 21 can be increased if desired.
• a plurality of different independent data rates will exist in the system.
• a data rate for painting the dynamic window buffer in the memory 16 will exist.
• Another data rate for decoding the encoded information from the dynamic window buffer will occur in the decoder in Fig. 4, and finally, the predetermined data rate to the printer will exist.

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