JP5520894B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly to bus arbitration when access to a bus competes in data transfer of an image to be printed.

  In color printing using an electrophotographic method, a color image is divided into a cyan component, a magenta component, a yellow component, and a black component, and each color is statically converted using cyan component data, magenta component data, yellow component data, and black component data. An electrostatic latent image is formed. Then, the electrostatic latent image of each color is developed with the toner of the color corresponding to the electrostatic latent image of each color to form a toner image, and the color toner image is transferred onto the fed paper and transferred to print the color image. .

  The transfer of each color component data developed in the memory is executed by a DMAC (Direct Memory Access Controller) assigned to each color component data. When accesses to the bus by these DMACs compete, bus arbitration is performed.

  As an example of conventional bus arbitration, the order of a plurality of devices is determined in descending order of the number of times a plurality of devices have used the bus within a preset period, and the priority of bus use is given according to the order. Techniques have been proposed (see, for example, Patent Document 1).

JP 2000-187640 A

  In electrophotographic image formation, an electrostatic latent image is formed by irradiating a photosensitive drum with laser from a laser scanning unit (LSU). For this reason, the data transferred to the LSU is required to have real-time properties. The state where data is not in time for the required timing is called underrun. When underrun occurs in data transferred to the LSU, an electrostatic latent image is not formed during that period, resulting in printing failure.

  An object of the present invention is to provide an image forming apparatus capable of more reliably preventing underrun during image printing.

  An image forming apparatus according to the present invention that achieves the above object has a function of executing color printing and monochrome printing. In the monochrome printing, color component data including black component data and white component dummy data is used. An image forming apparatus that performs printing with a color component having a data amount per main scanning line smaller than that of a black component, and in the color printing, black component data and color component data of a color image to be printed In the monochrome printing, the first DMA transfer request is sent to the memory, the bus, and the memory in which the black component data of the monochrome image to be printed and the color component data composed of the dummy data are developed. Therefore, the black component data of the color image is obtained in the color printing, and the black component data of the monochrome image is obtained in the monochrome printing. Each of the first DMA control unit including a first FIFO for temporarily storing the read black component data read from the memory using the bus, and a second DMA transfer request to the memory Thus, in the color printing, the color component data of the color image is read out from the memory using the bus, and the color component data including the dummy data of the monochrome image is read out from the memory in the monochrome printing. A second DMA control unit including a second FIFO to be temporarily stored; and a bus arbitration unit that arbitrates the right to use the bus when the first DMA transfer request and the second DMA transfer request compete with each other. , Using the black component data received through the first FIFO and the color component data received through the second FIFO. A printer engine that prints the color image on paper in the color printing, and prints the monochrome image on paper in the monochrome printing, and the first DMA control unit receives the first DMA transfer request when the first DMA transfer is requested. The first information obtained by converting the amount of black component data temporarily stored in the first FIFO into the number of main scanning lines is sent to the bus arbitration unit together with the first DMA transfer request, and the second The DMA controller sends second information obtained by converting the amount of color component data temporarily stored in the second FIFO into the number of main scanning lines at the time of the second DMA transfer request, and the second DMA transfer request. To the bus arbitration unit, and the bus arbitration unit, when the first DMA transfer request and the second DMA transfer request compete with each other, the number of main scanning lines indicated by the first information When The number of main scanning lines indicated by the second information is compared, and if the number of main scanning lines indicated by the first information is smaller than the number of main scanning lines indicated by the second information, the first information If the right to use the bus is given to the DMA controller, and the number of main scan lines indicated by the second information is smaller than the number of main scan lines indicated by the first information, the second DMA controller Is given the right to use the bus.

  The operation and effect of the present invention are as follows. When underrun occurs in black component data and color component data transferred to the printer engine, an electrostatic latent image is not formed during that period, resulting in printing failure. The number of main scanning lines that can be drawn with the amount of black component data temporarily stored in the first FIFO is compared with the number of main scanning lines that can be drawn with the amount of color component data temporarily stored in the second FIFO. The larger is the margin for underrun.

  The monochrome printing method in the image forming apparatus according to the present invention uses black component data and color component data composed of white component dummy data, and the amount of data per main scanning line is larger than the black component. This is a method of executing printing with fewer. In this method, the color component has a smaller amount of data per main scanning line than the black component. Therefore, even if the amount of black component data temporarily stored in the first FIFO and the amount of color component data temporarily stored in the second FIFO are the same, the main scan can be drawn with the amount of temporarily stored data. The number of lines is greater for color component data than for black component data.

  In the present invention, in monochrome printing, the first information obtained by converting the amount of black component data temporarily stored in the first FIFO at the time of the first DMA transfer request into the number of main scanning lines is the first DMA transfer request. They are sent to the bus mediation department together. Second information obtained by converting the amount of color component data temporarily stored in the second FIFO into the number of main scanning lines at the time of the second DMA transfer request is sent to the bus arbitration unit together with the second DMA transfer request. It is done. When the first DMA transfer request and the second DMA transfer request conflict, the number of main scanning lines indicated by the first information is compared with the number of main scanning lines indicated by the second information. If the number of main scanning lines indicated by the information 1 is smaller than the number of main scanning lines indicated by the second information, the right to use the bus is given to the first DMA controller. If the number of main scanning lines indicated by the second information is smaller than the number of main scanning lines indicated by the first information, the right to use the bus is given to the second DMA control unit.

  As described above, according to the present invention, the value obtained by converting the amount of black component data temporarily stored in the first FIFO into the number of main scanning lines and the color component data temporarily stored in the second FIFO. The right to use the bus is arbitrated by comparing the amount obtained by converting this amount into the number of main scanning lines. Accordingly, it is possible to more reliably prevent underrun during image printing.

  In monochrome printing, the amount of data per main scanning line is smaller than the black component of the color component, for example, the number of pixels per main scanning line and / or the number of bits (bytes) per pixel. It is to reduce.

  In the above configuration, the first look-up table in which the amount of black component data temporarily stored in the first FIFO and the first information are associated with each other, and temporarily stored in the second FIFO. A second look-up table that associates the amount of color component data with the second information, and the first DMA control unit stores the first FIFO in the first FIFO at the time of the first DMA transfer request. With respect to the amount of black component data temporarily accumulated, the first information corresponding to the amount of black component data is obtained with reference to the first look-up table, and the second DMA control unit For the amount of color component data temporarily stored in the second FIFO at the time of the second DMA transfer request, the second information corresponding to the amount of the color component data is used for the second lookup. Buru can be determined with reference to.

  According to this configuration, in the first lookup table, the amount of black component data temporarily stored in the first FIFO is associated with the first information, and in the second lookup table, the first information is associated with the first information. The amount of color component data temporarily stored in the second FIFO is associated with the second information. Therefore, the first information sent together at the time of the first DMA transfer request and the second information sent together at the time of the second DMA transfer request can be quickly obtained.

  In the above configuration, the image processing apparatus includes a storage unit that stores a program for executing the color printing and the monochrome printing. In the program, in the monochrome printing, a color component composed of the white component of the monochrome image per main scanning line. The amount of data is the same as the bus width of the bus.

  In monochrome printing, since the color component data consists of white component dummy data, it is possible to freely set the data amount per main scanning line for the color component. According to this configuration, in monochrome printing, the data amount of the color component composed of the white component of the monochrome image per main scanning line is made the same as the bus width of the bus. Accordingly, when the second DMA transfer request is generated once, the color component data for one main scanning line can be transferred. Therefore, in monochrome printing, handling of color component data in the program can be simplified.

  According to the present invention, underrun can be more reliably prevented during image printing.

1 is a perspective view illustrating an entire image forming apparatus according to an embodiment of the present disclosure. FIG. 2 is a diagram illustrating an internal structure of a main body of the image forming apparatus illustrated in FIG. 1. FIG. 2 is a block diagram illustrating a configuration of the image forming apparatus illustrated in FIG. 1. FIG. 2 is a block diagram illustrating a configuration of an image print processing unit provided in the image forming apparatus illustrated in FIG. 1. It is a figure which shows an example of a structure of 1st FIFO and 2nd FIFO. It is a figure which shows an example of a 1st lookup table. It is a figure which shows an example of the 2nd lookup table. 6 is a timing chart for explaining data transfer when a first DMA transfer request and a second DMA transfer request are not in conflict. 10 is a timing chart for explaining data transfer when a first DMA transfer request and a second DMA transfer request are in conflict (part 1). It is a figure which shows an example of the data accumulation amount of the 1st FIFO in the 1st, and the 2nd FIFO. 12 is a timing chart for explaining data transfer when a first DMA transfer request and a second DMA transfer request are in conflict (part 2). It is a figure which shows an example of the data accumulation amount of the 1st FIFO in the 2nd, and the 2nd FIFO.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a perspective view showing an entire image forming apparatus 1 according to an embodiment of the present invention. FIG. 2 is a diagram illustrating an internal structure of the apparatus main body 100 of the image forming apparatus 1. The image forming apparatus 1 can be applied to, for example, a digital multi-function peripheral having a copy, printer, scanner, and facsimile function. The image forming apparatus 1 includes an apparatus main body 100, a document reading unit 200, a document feeding unit 300, and an operation unit 400. In FIG. 2, the operation unit 400 is omitted.

  A document reading unit 200 is disposed on the apparatus main body 100, and a document feeding unit 300 is disposed on the document reading unit 200.

  The document feeder 300 functions as an automatic document feeder, and can continuously send a plurality of documents placed on the document placement unit 301 to the document reading unit 200.

  The document reading unit 200 includes a carriage on which an exposure lamp or the like is mounted, a document table made of a transparent member such as glass, a CCD (Charge Coupled Device) sensor, and a document reading slit (all not shown). The CCD sensor outputs the read original as image data.

  The apparatus main body 100 includes a sheet storage unit 101, an image forming unit 103, and a fixing unit 105. The sheet storage unit 101 is disposed at the lowermost part of the apparatus main body 100 and includes sheet cassettes 107 a to 107 d that can store a bundle of sheets. The paper cassettes 107a to 107d are configured in three stages. A sheet cassette 107a is disposed at the top, a sheet cassette 107b is disposed below the sheet cassette 107a, and sheet cassettes 107c and 107d are disposed side by side at the bottom.

  Among the sheet cassettes 107a to 107d, in the bundle of sheets stored in the selected cassette, the uppermost sheet is sent toward the sheet conveyance path 107 of the apparatus main body 100 by driving a pickup roller (not shown). . The sheet is conveyed to the image forming unit 103 through the sheet conveyance path 107.

  The sheet conveyance path 107 extends in a substantially vertical direction from the lower side to the upper side along one side surface (right side surface in FIG. 2) of the apparatus main body 100, and the other side surface (left side surface in FIG. 2) above. And extends substantially horizontally along the lower side of the document reading unit 200. A discharge tray 131 is provided at the end. Of the paper transport path 107, a portion extending in a substantially horizontal direction is a paper transport path 107e.

  The image forming unit 103 forms a toner image on the conveyed paper. The image forming unit 103 includes a yellow image forming unit 111Y, a magenta image forming unit 111M, a cyan image forming unit 111C, and a black image forming unit 111BK, which are arranged according to the order in which the toner images are transferred to the transfer belt 113. These units have the same configuration and will be described by taking the yellow image forming unit 111Y as an example.

  The yellow image forming unit 111Y includes a photosensitive drum 115 and an exposure device 117. Around the photosensitive drum 115, a charging device 119, a developing device 121, and a cleaning device 123 are arranged. The charging device 119 uniformly charges the peripheral surface of the photosensitive drum 115. The exposure device 117 generates light modulated in accordance with image data (image data output from the document reading unit 200, image data transmitted from a personal computer, image data received by facsimile), and is uniformly charged. Irradiate the peripheral surface of the photosensitive drum 115. As a result, an electrostatic latent image corresponding to yellow image data is formed on the peripheral surface of the photosensitive drum 115. In this state, by supplying yellow toner from the developing device 121 to the peripheral surface of the photosensitive drum 115, a toner image corresponding to yellow image data is formed on the peripheral surface.

  The transfer belt 113 can move counterclockwise while being sandwiched between the photosensitive drum 115 and the primary transfer roller 125. The yellow toner image is transferred from the photosensitive drum 115 to the transfer belt 113. The yellow toner remaining on the peripheral surface of the photosensitive drum 115 is removed by the cleaning device 123. The above is the description of the yellow image forming unit 111Y.

  Above the yellow image forming unit 111Y, the magenta image forming unit 111M, the cyan image forming unit 111C, and the black image forming unit 111BK, containers containing corresponding color toners, that is, a yellow toner container 127Y, a magenta toner container 127M, a cyan toner container 127C, and a black toner container 127BK are arranged. Each color developing device 121 is supplied with toner from a corresponding container.

  As described above, the yellow toner image is transferred to the transfer belt 113, and the magenta toner image is transferred onto the toner image. Similarly, the cyan toner image and the black toner image are transferred onto the transfer belt 113. As a result, a color toner image is formed on the transfer belt 113. In this way, a toner image of each color pattern is superimposed and transferred onto the transfer belt 113, whereby a color toner image is formed on the transfer belt 113. The color toner image is transferred by the secondary transfer roller 129 onto the sheet conveyed from the sheet storage unit 101 described above.

  The sheet on which the color toner image is transferred is sent to the fixing unit 105. The fixing unit 105 includes a heating roller and a fixing roller. The paper on which the color toner image is transferred is sandwiched between these rollers. As a result, heat and pressure are applied to the color toner image and the paper, and the color toner image is fixed to the paper. The sheet is discharged to a discharge tray 131.

  The operation unit 400 includes an operation key unit 401 and a display unit 403. The display unit 403 has a touch panel function, and displays a screen including soft keys. The user operates the soft keys while viewing the screen to make settings necessary for executing functions such as copying.

  The operation key unit 401 is provided with operation keys including hard keys. Specifically, a function switch key for switching between a start key, a numeric keypad, a stop key, a reset key, a copy, a printer, a scanner, and a facsimile is provided.

  The start key is a key for starting operations such as copying and facsimile transmission. The numeric keypad is a key for inputting numbers such as the number of copies and a facsimile number. The stop key is a key for stopping the copy operation or the like halfway. The reset key is a key for returning the set contents to the initial setting state.

  The function switching key includes a copy key, a transmission key, and the like, and is a key for switching between a copy function, a transmission function, and the like. When the copy key is operated, an initial copy screen is displayed on the display unit 403. When the transmission key is operated, an initial screen for facsimile transmission and mail transmission is displayed on the display unit 403.

  FIG. 3 is a block diagram showing the configuration of the image forming apparatus 1 shown in FIG. The image forming apparatus 1 has a configuration in which an apparatus main body 100, a document reading unit 200, a document feeding unit 300, an operation unit 400, a control unit 500, and a communication unit 600 are connected to each other by a bus. Since the apparatus main body 100, the document reading unit 200, the document feeding unit 300, and the operation unit 400 have already been described, description thereof will be omitted.

  The control unit 500 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), an image memory, and the like. The CPU executes control necessary for operating the image forming apparatus 1 on the above-described components of the image forming apparatus 1 such as the apparatus main body 100. The ROM stores software necessary for controlling the operation of the image forming apparatus 1. The RAM is used for temporary storage of data generated during execution of software, storage of application software, and the like. The image memory temporarily stores image data (image data output from the document reading unit 200, image data transmitted from a personal computer, image data received by facsimile, etc.).

  The control unit 500 has the function of the image print processing unit 501. This will be described later.

  The communication unit 600 includes a facsimile communication unit 601 and a network I / F unit 603. The facsimile communication unit 601 includes an NCU (Network Control Unit) for controlling connection of a telephone line with a destination facsimile and a modulation / demodulation circuit for modulating / demodulating a signal for facsimile communication. The facsimile communication unit 601 is connected to the telephone line 605.

  A network I / F unit 603 is connected to a LAN (Local Area Network) 607. A network I / F unit 603 is a communication interface circuit for executing communication with a terminal device such as a personal computer connected to the LAN 607.

  FIG. 4 is a block diagram illustrating a configuration of the image print processing unit 501. The image print processing unit 501 has a configuration in which the CPU 11, the EEPROM 13, the DRAM 15, the first DMA control unit 17, and the second DMA control units 19 </ b> C, 19 </ b> M, and 19 </ b> Y are connected to the bus 21. The image print processing unit 501 further includes a bus arbitration unit 35, a first image processing unit 23, and second image processing units 29C, 29M, and 29Y.

  The EEPROM 13 is an example of a storage unit, and stores programs for executing color printing and monochrome printing in advance. In this program, the amount of data per main scanning line of black and color components (cyan component, magenta component, yellow component) in color printing, and color component (cyan component) consisting of black and white components in monochrome printing. , Magenta component, yellow component) per one main scanning line is determined. As will be described later, in monochrome printing, the amount of data per main scanning line of the color component composed of the white component of the monochrome image is made the same as the bus width of the bus 21.

  The CPU 11 controls the operation of the image print processing unit 501 in accordance with the program stored in the EEPROM 13.

  The DRAM 15 is an example of a memory, and print data of an image to be printed described in PDL (page description language) is developed as dot data. More specifically, in color printing, dot data of black component data D1, cyan component data D2, magenta component data D3, and yellow component data D4 of a color image to be printed is developed in the DRAM 15. Cyan component data D2, magenta component data D3, and yellow component data D4 are color component data.

  In monochrome printing, dot data of black component data D1, cyan component data D2, magenta component data D3, and yellow component data D4 of a monochrome image to be printed is developed in the DRAM 15. Cyan component data D2, magenta component data D3, and yellow component data D4 are color component data. In monochrome printing, the color component data is white component dummy data.

  Color printing handles black component data, cyan component data, magenta component data, and yellow component data, but monochrome printing requires separate printing programs for color printing and monochrome printing if only black component data is handled. Become. As in the present embodiment, by handling cyan component data, magenta component data, and yellow component data even in monochrome printing, the printing program can be shared between color printing and monochrome printing.

  When handling cyan component data, magenta component data, and yellow component data in monochrome printing, these color component data are not printed because they are dummy data of white components. For this reason, in the printing program, the amount of data per main scanning line at the time of printing is smaller than that of the black component for the color component. This reduces the burden on the CPU 11 and the like. In monochrome printing, reducing the amount of data per line of main scanning than that of black components means, for example, reducing the number of pixels per main scanning line and / or the number of bits (bytes) per pixel. That is.

  The first DMA control unit 17 transfers the black component data D1 developed in the DRAM 15 to the first image processing unit 23 instead of the CPU 11 when the CPU 11 is given the authority to transfer data. When the first DMA control unit 17 executes the transfer of the black component data D1, the first DMA control unit 17 uses the bus 21 to send the first DMA transfer request R1 to the DRAM 15. As a result, the black component data D1 developed in the DRAM 15 is transferred to the first image processing unit 23 using the bus 21.

  The first DMA control unit 17 includes a first FIFO 25 and a first lookup table 27. These will be described later.

  The second DMA control unit 19C transfers the cyan component data D2 expanded in the DRAM 15 to the second image processing unit 29C instead of the CPU 11 when the CPU 11 is given the authority to transfer data. When the second DMA control unit 19C executes the transfer of the cyan component data D2, the second DMA control unit 19C sends a second DMA transfer request R2 to the DRAM 15 using the bus 21. As a result, the cyan component data D2 developed in the DRAM 15 is transferred to the second image processing unit 29C using the bus 21. The second DMA control unit 19M performs the same processing as the second DMA control unit 19C for the magenta component data D3 and the second DMA control unit 19Y for the yellow component data D4. If there is no need to distinguish between the second DMA control units 19C, 19M, and 19Y, they are referred to as a second DMA control unit 19.

  The second DMA control unit 19C includes a second FIFO 31C and a second lookup table 33C. The second DMA control unit 19M includes a second FIFO 31M and a second lookup table 33M. The second DMA control unit 19Y includes a second FIFO 31Y and a second lookup table 33Y. These will be described later.

  The bus arbitration unit 35 includes a first DMA transfer request R1 for black component data D1, a second DMA transfer request R2 for cyan component data D2, a second DMA transfer request R3 for magenta component data D3, and When at least two of the second DMA transfer requests R4 for the yellow component data D4 are in conflict, the DMA control unit arbitrates which DMA controller is given the right to use the bus 21.

  The first image processing unit 23 performs zoom processing, filter processing, and the like on the black component data D1. The zoom process is a process for enlarging or reducing an image in the main scanning direction. A filter is a process for smoothing or enhancing an image. The black component data D1 processed by the first image processing unit 23 is sent to the exposure device 117 of the black image forming unit 111BK, and beam light for forming a black component electrostatic latent image is generated.

  The second image processing unit 29C performs zoom processing, filter processing, and the like on the cyan component data D2. The cyan component data D2 processed by the second image processing unit 29C is sent to the exposure device 117 of the cyan image forming unit 111C, and beam light for forming an electrostatic latent image of the cyan component is generated.

  The second image processing unit 29M executes zoom processing, filter processing, and the like on the magenta component data D3. The magenta component data D3 processed by the second image processing unit 29M is sent to the exposure device 117 of the magenta image forming unit 111M, and beam light for forming an electrostatic latent image of the magenta component is generated.

  The second image processing unit 29Y performs zoom processing, filter processing, and the like on the yellow component data D4. The yellow component data D4 processed by the second image processing unit 29Y is sent to the exposure device 117 of the yellow image forming unit 111Y to generate beam light for forming a yellow component electrostatic latent image. If there is no need to distinguish between the second image processing units 29C, 29M, and 29Y, they are referred to as a second image processing unit 29.

  The exposure devices 117 of the black image forming unit 111BK, the cyan image forming unit 111C, the magenta image forming unit 111M, and the yellow image forming unit 111Y are laser scanning units (LSU).

  As described above, the data of each color component processed by the image print processing unit 501 is sent to the exposure device 117 for each color of the printer engine 133. The printer engine 133 includes a black image forming unit 111BK, a cyan image forming unit 111C, a magenta image forming unit 111M, and a yellow image forming unit 111Y. The printer engine 133 uses the black component data D1 received through the first FIFO 25 and the color component data (cyan component data D2, magenta component data D3, yellow component data D4) received through the second FIFOs 31C, 31M, and 31Y. In color printing, a color image is printed on paper, and in monochrome printing, a monochrome image is printed on paper.

  The first FIFO 25 and the second FIFOs 31C, 31M, 31Y will be described. The second FIFO will be described using the second FIFO 31C for cyan component data, but the same can be said for the second FIFOs 31M and 31Y for magenta component data and yellow component data.

  The black component data D1 processed by the first image processing unit 23 is transferred to the exposure device 117 of the black image forming unit 111BK. If an underrun occurs in the black component data D1 transferred to the exposure device 117, a black component electrostatic latent image cannot be formed during that period. Similarly, the cyan component data D2 processed by the second image processing unit 29C is transferred to the exposure device 117 of the cyan image forming unit 111C. If an underrun occurs in the cyan component data D2 transferred to the exposure device 117, an electrostatic latent image of the cyan component cannot be formed during that period.

  In order to prevent the occurrence of underrun in the black component data D1, the first FIFO 25 is provided, and the black component data D1 read from the DRAM 15 by the first DMA control unit 17 is temporarily stored in the first FIFO 25. To do. The black component data D1 read from the DRAM 15 is sent to the first image processing unit 23 through the first FIFO 25. Similarly, in order to prevent underrun from occurring in the cyan component data D2, the second FIFO 31C is provided, and the cyan component data D2 read from the DRAM 15 by the second DMA control unit 19C is converted into the second FIFO 31C. Temporarily accumulate in The cyan component data D2 read from the DRAM 15 is sent to the second image processing unit 29C through the second FIFO 31C.

  FIG. 5 is a diagram illustrating an example of the configuration of the first FIFO 25 and the second FIFO 31C. Each of the first FIFO 25 and the second FIFO 31C is a 1000-stage FIFO, and one stage is 8 bits.

  In color printing, one main scanning line of black component and cyan component is, for example, 5000 pixels, and one pixel is, for example, 8 bits. Therefore, if the first FIFO 25 is full, the black component data D1 corresponding to 0.2 main scanning lines is accumulated. Similarly, if the second FIFO 31C is full, cyan component data D2 corresponding to 0.2 main scanning lines is accumulated.

  On the other hand, in monochrome printing, one main scanning line of the black component is 5000 pixels as in color printing, and one pixel is 8 bits. However, one main scanning line of the cyan component is, for example, 128 pixels, and one pixel is, for example, 1 bit. In monochrome printing, since the cyan component is a white component dummy, one pixel can be expressed by one bit, the number of pixels in one main scanning line is 128, and the bus width of the bus 21 is the same.

  In monochrome printing, if the first FIFO 25 is full, the black component data D1 for the main scanning line of 0.2 lines is accumulated. On the other hand, if the second FIFO 31C is full, the cyan component data D2 corresponding to 62.5 main scanning lines is accumulated.

  Thus, in monochrome printing, the color component (cyan component, magenta component, yellow component) has a smaller number of pixels constituting one main scanning line and a smaller number of bits constituting one pixel than the black component. Even if the amount of data stored in the second FIFO 25 and the second FIFO 31C, 31M, 31Y is the same, the margin for underrun is different. If the number of main scanning lines is large, there is a margin for underrun.

  FIG. 6 is a diagram illustrating an example of the first lookup table 27 provided in the first DMA control unit 17. FIG. 7 is a diagram illustrating an example of the second lookup table 33C provided in the second DMA control unit 19C. The second look-up table will be described using the second look-up table 33C for cyan component data, but the same applies to the second look-up tables 33M and 33Y for magenta component data and yellow component data. I can say that.

  The first look-up table 27 indicates the amount of black component data D1 temporarily stored in the first FIFO 25 and the value obtained by converting those data amounts into the number of main scanning lines (first information I1) in monochrome printing. ). The second look-up table 33C has an amount of cyan component data D2 temporarily accumulated in the second FIFO 31C and a value obtained by converting these data amounts into the number of main scanning lines (second information I2) in monochrome printing. ).

  The first DMA controller 17 uses the first information corresponding to the amount of black component data D1 for the amount of black component data D1 temporarily stored in the first FIFO 25 at the time of the first DMA transfer request R1. I1 is obtained by referring to the first look-up table 27. The first DMA control unit 17 sends the first information I1 to the bus arbitration unit 35 together with the first DMA transfer request R1.

  The second DMA control unit 19C obtains the second information I2 corresponding to the cyan component data D2 with respect to the amount of the cyan component data D2 temporarily stored in the second FIFO 31C at the time of the second DMA transfer request R2. , By referring to the second lookup table 33C. The second DMA control unit 19C sends the second information I2 to the bus arbitration unit 35 together with the second DMA transfer request R2.

  The second DMA controller 19M uses the second information corresponding to the amount of magenta component data D3 for the amount of magenta component data D3 temporarily stored in the second FIFO 31M at the time of the second DMA transfer request R3. I3 is obtained by referring to the second lookup table 33M. The second DMA control unit 19M sends the second information I3 to the bus arbitration unit 35 together with the second DMA transfer request R3.

  The second DMA control unit 19Y obtains the second information I4 corresponding to the yellow component data D4 with respect to the amount of yellow component data D4 temporarily stored in the second FIFO 31Y at the time of the second DMA transfer request R4. , By referring to the second lookup table 33Y. The second DMA control unit 19Y sends the second information I4 together with the second DMA transfer request R4 to the bus arbitration unit 35.

  The bus arbitration unit 35 will be described. The color component data will be described using the cyan component data D2, but the same applies to the magenta component data D3 and the yellow component data D4. FIG. 8 is a timing chart for explaining data transfer when the first DMA transfer request R1 and the second DMA transfer request R2 are not in conflict.

  Both the first DMA transfer request R1 and the second DMA transfer request R2 are active when they are at the H level and inactive when they are at the L level. If the period in which the first DMA transfer request R1 is active and the period in which the second DMA transfer request R2 is active overlap, the first DMA transfer request R1 and the second DMA transfer request R2 compete.

  As shown in FIG. 8, if the first DMA transfer request R1 and the second DMA transfer request R2 do not conflict, the bus arbitration unit 35 does not arbitrate the right to use the bus 21. The first DMA control unit 17 reads the black component data D1 developed in the DRAM 15 shown in FIG. 4 during the period in which the first DMA transfer request R1 is active, and passes through the first FIFO 25 to 1 to the image processing unit 23. The second DMA control unit 19C reads the cyan component data D2 developed in the DRAM 15 during the period in which the second DMA transfer request R2 is active, and performs the second image processing via the second FIFO 31C. The data is transferred to the unit 29C.

  FIG. 9 is a timing chart for explaining data transfer when the first DMA transfer request R1 and the second DMA transfer request R2 are in conflict. For example, as shown in FIG. 10, the amount of black component data D1 temporarily stored in the first FIFO 25 at the time of the first DMA transfer request R1 is set to 500, and the second level at the time of the second DMA transfer request R2. The amount of cyan component data D2 temporarily stored in the FIFO 31C is 16 stages.

  The first DMA control unit 17 converts the black component data D1 temporarily stored in the first FIFO 25 at the time of the first DMA transfer request R1 into a conversion value (first information) corresponding to the black component data D1. Is obtained with reference to the first lookup table 27 shown in FIG. In this case, 0.1 (that is, the main scanning line is 0.1 line).

  The second DMA control unit 19C obtains a conversion value (second information) corresponding to the cyan component data for the cyan component data D2 temporarily stored in the second FIFO 31C at the time of the second DMA transfer request R2. This is obtained with reference to the second look-up table 33C shown in FIG. In this case, it is 1.0 (that is, the main scanning line is 1.0 line).

  The bus arbitration unit 35 compares the converted value (0.1) for the black component data D1 with the converted value (1.0) for the cyan component data D2, and the converted value of the black component data D1 is the cyan component data D2. Therefore, the right to use the bus 21 is given to the first DMA controller 17. Therefore, during the period Ta in which the first DMA transfer request R1 is active and the second DMA transfer request R2 is active, the first DMA control unit 17 performs the black component data D1 developed in the DRAM 15. Is transferred to the first image processing unit 23 via the first FIFO 25. During the period Ta, the second DMA control unit 19C cannot read the cyan component data D2 developed in the DRAM 15. After the end of the period Ta, the second DMA control unit 19C reads the cyan component data D2 developed in the DRAM 15 and transfers it to the second image processing unit 29C via the second FIFO 31C.

  FIG. 11 is a timing chart for explaining data transfer when the first DMA transfer request R1 and the second DMA transfer request R2 compete with each other as in FIG. For example, as shown in FIG. 12, the amount of black component data temporarily stored in the first FIFO 25 at the time of the first DMA transfer request R1 is 800, and the second DMA transfer request R2 The amount of cyan component data temporarily stored in the FIFO 31C is assumed to be two stages.

  The first DMA control unit 17 converts the black component data D1 temporarily stored in the first FIFO 25 at the time of the first DMA transfer request R1 into a conversion value (first information) corresponding to the black component data D1. Is obtained with reference to the first lookup table 27 shown in FIG. In this case, it is 0.16 (that is, the main scanning line is 0.16 lines).

  For the cyan component data D2 temporarily stored in the second FIFO 31C at the time of the second DMA transfer request R2, the second DMA control unit 19C converts the converted value (second information) corresponding to the cyan component data D2. Is obtained with reference to the second look-up table 33C shown in FIG. In this case, it is 0.125 (that is, the main scanning line is 0.125 lines).

  The bus arbitration unit 35 compares the converted value (0.16) for the black component data D1 with the converted value (0.125) for the cyan component data D2, and the converted value of the cyan component data D2 is the black component data D1. Therefore, the right to use the bus 21 is given to the second DMA controller 19C. Accordingly, during the period Tb in which the first DMA transfer request R1 is active and the second DMA transfer request R2 is active, the second DMA control unit 19C has the cyan component data D2 developed in the DRAM 15 Is transferred to the second image processing unit 29C via the second FIFO 31C. During the period Tb, the first DMA control unit 17 cannot read the black component data D1 developed in the DRAM 15. After the end of the period Tb, the first DMA control unit 17 reads the black component data D1 developed in the DRAM 15 and transfers it to the first image processing unit 23 via the first FIFO 25.

  The main effects of this embodiment will be described. Although a description will be given using a cyan component as a color component, the same applies to a magenta component and a yellow component. Referring to FIG. 4, when an underrun occurs in black component data D1 and cyan component data D2 transferred to printer engine 133, an electrostatic latent image is not formed during that period, resulting in a printing failure. The number of main scanning lines that can be drawn with the amount of black component data D1 temporarily stored in the first FIFO 25 and the number of main scanning lines that can be drawn with the amount of cyan component data D2 temporarily stored in the second FIFO 31C. In comparison, the larger one has a greater margin for underrun.

  The monochrome printing method in the image forming apparatus 1 according to the present embodiment uses black component data D1 and cyan component data D2 composed of white component dummy data, and the cyan component per main scanning line rather than the black component. This is a method for executing printing with a reduced amount of data. In this method, the cyan component has a smaller amount of data per main scanning line than the black component. Therefore, even if the amount of black component data D1 temporarily stored in the first FIFO 25 and the amount of cyan component data D2 temporarily stored in the second FIFO 31C are the same, the amount of data temporarily stored can be drawn. As for the number of main scanning lines, the cyan component data D2 is larger than the black component data D1.

  In the present embodiment, in monochrome printing, the first information I1 obtained by converting the amount of black component data D1 temporarily stored in the first FIFO 25 into the number of main scanning lines at the time of the first DMA transfer request R1 is the first information. The DMA transfer request R1 is sent to the bus arbitration unit 35. The second information I2 obtained by converting the amount of cyan component data D2 temporarily stored in the second FIFO 31C into the number of main scanning lines at the time of the second DMA transfer request R2 together with the second DMA transfer request R2 It is sent to the bus arbitration unit 35. When the first DMA transfer request R1 and the second DMA transfer request R2 compete, the number of main scanning lines indicated by the first information I1 and the number of main scanning lines indicated by the second information I2 are determined. In comparison, if the number of main scanning lines indicated by the first information I1 is smaller than the number of main scanning lines indicated by the second information I2, the right to use the bus 21 is given to the first DMA control unit 17. If the number of main scanning lines indicated by the second information I2 is smaller than the number of main scanning lines indicated by the first information I1, the right to use the bus 21 is given to the second DMA control unit 19C.

  As described above, according to the present embodiment, a value obtained by converting the amount of the black component data D1 temporarily stored in the first FIFO 25 into the number of main scanning lines and cyan temporarily stored in the second FIFO 31C. The right to use the bus 21 is arbitrated by comparing the amount of the component data D2 with the value converted into the number of main scanning lines. Accordingly, it is possible to more reliably prevent underrun during image printing.

  Further, according to the present embodiment, in the first lookup table 27 shown in FIG. 6, the amount of the black component data D1 temporarily accumulated in the first FIFO 25 is associated with the first information I1. In the second lookup table 33C shown in FIG. 7, the amount of cyan component data D2 temporarily stored in the second FIFO 31C is associated with the second information I2. Therefore, the first information I1 sent together at the time of the first DMA transfer request R1 and the second information I2 sent together at the time of the second DMA transfer request R2 can be quickly obtained.

  Furthermore, according to the present embodiment, in monochrome printing, the data amount of the cyan component consisting of the white component of the monochrome image per main scanning line is made the same as the bus width (128) of the bus 21. Thus, when the second DMA transfer request R2 is generated once, the cyan component data D2 for one main scanning line can be transferred. Therefore, in monochrome printing, handling of the cyan component data D2 in the program can be simplified.

  Although the electrophotographic image forming apparatus 1 has been described as an example of the present embodiment, the present invention can also be applied to an inkjet image forming apparatus.

1 Image forming apparatus 13 EEPROM (an example of a storage unit)
15 DRAM (an example of memory)
17 First DMA controller 19, 19C, 19M, 19Y Second DMA controller 21 Bus 25 First FIFO
33, 33C, 33M, 33Y Second FIFO
35 Bus Mediation Department

Claims (3)

It has a function of executing color printing and monochrome printing. In the monochrome printing, color component data composed of black component data and white component dummy data is used, and the color component per main scanning line is higher than the black component. An image forming apparatus that executes printing with a reduced amount of data,
In the color printing, the black component data and color component data of the color image to be printed are expanded, and in the monochrome printing, the black component data of the monochrome image to be printed and the color component data including the dummy data are expanded. Memory and
With bus,
By sending a first DMA transfer request to the memory, the black component data of the color image is read from the memory using the bus, and the black component data of the monochrome image is read from the memory in the monochrome printing. A first DMA control unit including a first FIFO for temporarily storing the read black component data;
By sending a second DMA transfer request to the memory, the color printing uses the color component data of the color image, and the monochrome printing uses the color component data consisting of the dummy data of the monochrome image, respectively. A second DMA control unit including a second FIFO for temporarily storing the read color component data.
A bus arbitration unit that arbitrates the right to use the bus when the first DMA transfer request and the second DMA transfer request conflict;
Using the black component data received through the first FIFO and the color component data received through the second FIFO, the color image is printed on the paper in the color printing, and the monochrome image is printed on the paper in the monochrome printing. A printer engine for printing,
The first DMA control unit converts the first information obtained by converting the amount of black component data temporarily stored in the first FIFO into the number of main scanning lines at the time of the first DMA transfer request. To the bus arbitration unit together with the DMA transfer request of
The second DMA control unit converts the second information obtained by converting the amount of color component data temporarily stored in the second FIFO into the number of main scanning lines at the time of the second DMA transfer request. To the bus arbitration unit together with the DMA transfer request of
The bus arbitration unit, when the first DMA transfer request and the second DMA transfer request compete with each other, the number of main scanning lines indicated by the first information and the main information indicated by the second information. If the number of main scanning lines indicated by the first information is smaller than the number of main scanning lines indicated by the second information, the bus is used by the first DMA controller. If the number of main scanning lines indicated by the second information is smaller than the number of main scanning lines indicated by the first information, the image gives the right to use the bus to the second DMA control unit. Forming equipment. A first lookup table that associates the amount of black component data temporarily accumulated in the first FIFO with the first information;
A second lookup table that associates the amount of color component data temporarily stored in the second FIFO with the second information;
The first DMA control unit obtains the first information corresponding to the amount of black component data for the amount of black component data temporarily stored in the first FIFO at the time of the first DMA transfer request. , Referring to the first look-up table,
The second DMA control unit obtains the second information corresponding to the amount of color component data for the amount of color component data temporarily stored in the second FIFO at the time of the second DMA transfer request. The image forming apparatus according to claim 1, wherein the image forming apparatus is obtained with reference to the second look-up table. A storage unit for storing a program for executing the color printing and the monochrome printing;
3. The program according to claim 1, wherein in the monochrome printing, a data amount of a color component composed of the white component of the monochrome image per main scanning line is the same as a bus width of the bus. Image forming apparatus.

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