JPH08276642A - Image forming apparatus equipped with paper transfer controlling device - Google Patents

Abstract

PURPOSE: To reduce a burden of paper control on CPU of an image data controller and an image formation controller and to increase the speed of printing operation by installing a paper transfer controller and a random access memory which is possessed commonly by the paper transfer controller and an image data controller. CONSTITUTION: CPU communicates with a paper supply-discharge apparatus through a paper handling interface 12, controls a paper supply deck and a paper discharge apparatus, and collects status information of those apparatuses. Also, CPU 13 exchanges information with a video controller 9 through a dual port memory. In addition, CPU 13 takes up the branch signals of signals /PRINT, /VSYNC, /PDLV, /SPCHG, /PFED of the video interface between the video controller 9 and an engine controller 8 to determine paper supply- discharge timing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention controls a paper feeding / discharging device of an image forming apparatus by a dedicated paper conveying control device separate from the image forming control device to improve the performance of the entire image forming device. Is.

[0002]

2. Description of the Related Art Conventionally, an image forming apparatus using an electrophotographic system is provided with an image forming control device for controlling the entire electrophotographic process including a paper feeding / discharging process to collectively control the entire image forming device. I was going. Further, in the conventional apparatus, when the paper feeding / discharging apparatus is added as an option, these additional apparatuses are connected to the image forming control apparatus in a one-to-one manner.

Further, a command for moving the paper feeding / discharging device and status information of these devices have been issued through the image forming control device.

[0004]

However, in recent years, there has been a demand for a common image forming unit, which is the heart of the image forming apparatus, and the sheet feeding and discharging apparatus around the image forming section to be rearranged according to the user's application. did it. In such a case, in the conventional configuration, it is necessary to replace the image forming control device itself or to previously incorporate control programs and interfaces of all the paper feeding and discharging devices connectable to the image forming control device.

Further, since the command and status of the paper feeding / discharging device are performed through the image forming control device, the load on the CPU of the image forming control device becomes heavy. Recently, in order to promote user friendliness, there is a desire to display the movement and status of the image forming apparatus to the user in as much detail as possible in real time, and it is necessary to send the status signals of the paper feeding and discharging apparatuses to the host computer side by side. There is.

In such a case, there is a problem that the communication speed is delayed and the amount of information is insufficient if the image forming control device is interposed therebetween. In order to solve this problem, an expensive CPU must be used as the CPU of the image forming control device, or the image forming control device has a large-capacity random access memory, and the status information of the paper feeding and ejecting device is displayed. You have to remember it.

Therefore, the first object of the present invention is to reduce the load of the CPU of the image information control device and the CPU of the image formation control device for paper management and to speed up the original printing operation of the image forming device. It is to provide a device.

A second object of the present invention is to provide an image forming apparatus capable of minimizing changes in the image information control apparatus and the image forming control apparatus when the paper feeding and discharging apparatus is recombined. Is.

A third object of the present invention is to provide an image forming apparatus which is provided with a CPU dedicated to control of sheet conveyance to comprehensively manage the movement of paper in the image forming apparatus, eliminates dead time and realizes the highest throughput. May be provided.

A fourth object of the present invention is to provide an image forming apparatus capable of promptly informing the user of the status of the image forming apparatus.

A fifth object of the present invention is to provide an image forming apparatus in which the memory of the image information control apparatus is occupied for a short time so that the memory can be used efficiently.

A sixth object of the present invention is to provide an image forming apparatus in which the sheet conveying control device judges the state of the sheet feeding apparatus and selects the optimum sheet feeding source to maximize the throughput of the image forming apparatus. That is.

[0013]

In order to achieve the above object, according to the present invention, firstly, a paper conveyance control device is provided so that the CPU of the image information control device can concentrate on the control of the image information and the image formation control. The CPU of the device dedicates itself to image formation and releases it from the management of the paper feeding / discharging device, speeds up the original printing operation of the image forming device, and controls the paper conveyance even if the paper feeding / discharging device is reconfigured. It is only necessary to replace the program of the apparatus, and the change of the image information control apparatus and the image formation control apparatus is minimized.

Secondly, according to the present invention, a dedicated CPU is provided in the paper transport control device to integrally manage the movement of the paper in the image forming apparatus, and printing is performed so that the fastest throughput can be obtained from the paper transport control device. Permission information is provided to optimally control the image forming apparatus.

Thirdly, according to the present invention, the paper conveyance control device is provided with a memory for sharing information with the image information control device, the image information control device receives a schedule of pages to be printed, and the paper conveyance control device performs a printing operation. Get the fastest throughput by moving the paper prior to. At the same time, the movement of the paper currently moving in the image forming apparatus is captured step by step in the shared memory, and the movement of the paper is sent to the host computer side via the image information control device, so that the status of the image forming apparatus is notified to the user. I can inform you quickly.

Fourthly, according to the present invention, when the paper conveyance control device quickly catches the movement of the paper moving in the image forming apparatus and confirms that the paper discharge is completed successfully, the image information is detected when a jam or an error occurs. By providing the information that the data retained in the image memory for re-outputting the image by the control device can be erased, the time for which the image information control device occupies the image memory is minimized. In particular, when the image forming apparatus becomes multifunctional and the number of paper feed ports and paper ejection ports increases, the time remaining in the device changes for each paper. The sheets are not ejected in the order in which they were fed. In the past, the image memory was cleared after all paper was ejected, but it is better to clear the image memory for paper ejected earlier so that the memory can be used effectively. In the present invention, a RAM release flag is provided for each page,
The memory can be cleared for each page.

Fifthly, according to the present invention, the sheet conveyance control device knows the print schedule in advance and quickly picks up the state of the sheet feeding device to judge the state of the sheet feeding device and select the optimum sheet feeding source. . For example, if there is no more paper in the designated paper source, another substitute paper source is selected, or if a paper source with a high transport speed is available, that paper source is selected.

[0018]

Embodiments of the present invention will now be described with reference to the drawings.

(Embodiment 1) FIG. 1 is a circuit block diagram of a paper conveyance controller (paper handling controller: abbreviated as PHC) of the present invention and a connection interface between the PHC and an image information controller (called a video controller). Show.

Before entering the description of FIG. 1, the overall configuration of the image forming apparatus will be described with reference to FIG. In FIG. 2, reference numeral 1 denotes an image forming apparatus main body, which is a printer equipped with a known electrophotographic laser beam writing apparatus. Reference numeral 2 is a display unit of the main body 1. A double-sided unit 3 is a device for reversing the paper once printed, returning to paper feeding, and printing again on the back side.
Reference numeral 4 denotes an envelope feeder, which is an envelope paper feeding device used for printing envelopes. A multi-purpose tray 5 feeds a small amount of irregular size paper. 6 is a large-capacity paper feed deck. A staple finisher 7 is a paper discharge device for stapling and stacking the paper discharged from the main body. Of these, 3, 4, 6, and 7 are optional devices that are sold separately from the main body.

Next, the arrangement and relationship of each control device will be described with reference to FIG. Reference numeral 8 denotes an image forming control device for controlling the image forming operation of the main body, which is commonly referred to as an engine controller, and performs electrophotographic process control, double-sided unit in the main body, and paper conveyance timing control of the envelope feeder. An image information control device, commonly called a video controller 9, receives data to be printed from a host computer and creates image information to be printed. Reference numeral 10 denotes a paper conveyance control device, commonly called a paper handling controller (abbreviated as PHC), which performs overall control of the paper feed deck and the finisher 7. 12 is
An interface cable that connects the paper feeding and discharging device to the PHC is called a paper handling interface.

Now, returning to FIG. 1, the contents will be described. A CPU 13 is an 8-bit microcomputer. Reference numeral 14 is a type of random access memory dual port memory having an arbitration function. Reference numeral 15 is a read-only memory, which is mounted in a socket and is replaceable. Reference numeral 16 is a buffer amplifier for the interface. Reference numeral 17 is a reset circuit, which is an external reset signal / R.
Reset with ESET. Reference numeral 18 is a buffer amplifier for the interface.

The main constitution of the PHC 10 is as described above. The CPU 13 communicates with the paper feeding / discharging device via the paper handling interface 12, controls the paper feeding deck 6 and the paper discharging device 7, and collects status information of these devices. The CPU 13 also exchanges information with the video controller 9 via the dual port memory. Further, the CPU 13 uses the signals / PRNT, / VSYNC, / PDLV, / SP of the video interface between the video controller 9 and the engine controller 8.
A branch of CHG and / PFED is taken in to determine the paper feed / discharge timing.

The types of each signal are as follows. D0 to D7: For DUALPORT MEMORY 8-bit data line AD0 to AD10: For DUALPORT MEMORY
11-bit address line / CS: DUALPORTM
EMORY chip select line / OE: DUALPORTM MEMORY output enable line / WE: DUALPORTM MEMORY enable enable line / BUSY: DUALPORT MEMORY busy line / PRINT signal: Print command issued by the video controller 9 to the engine controller 8 / VSYNC signal: Engine controller Sub-scanning synchronization signal issued by 8 / PFED signal: Feeding reminder signal issued by the engine controller 8 to the feeding deck 6 / SPCHG signal: Matching the paper feeding speed issued by the engine controller 8 to the feeding deck 6 with the internal feeding speed / PDLV signal: A signal that informs the timing when the engine controller 8 ejects paper from the exit of the main body / RESET signal: This signal is an option Signal for resetting CPU of controller by hardware Note that the symbol “/” indicates low level active.

Next, the video controller 9 and the PHC 10
The exchange of information via the memory 14 between the two will be described in some more detail. The dual port memory is divided into the following three types of parts. 1 Transport status management area 000h to 3D1h 2 Command & status management area 400h to 7FDh 3 Startup processing area 7FEh to 7FFh

Below, the transport status management area, command &
Defined separately from the status management area. The conveyance status management area is used to specify the paper conveyance operation. The command & status management area is used for detailed management of CONFIGURATION (connection status) and status of the paper feeding / discharging device.

Further, when changing the data of the transport status management area once written, the transport status management area change request command is used. The command on the left is command &
It is processed as one of the normal commands using the status management area.

Conveyance status management area: (1) The video controller 9 controls the printing of each image.
The paper feed port, the paper size, the paper discharge port, and the paper discharge process are written in the transport status management area, and an operation start instruction is given. (2) The PHC 10 controls the paper feed deck 6, the main body 1, and the paper discharge finisher 7 in accordance with the above instructions, and manages the entire paper conveyance. The PHC 10 notifies the video controller of the paper transport state in real time. (3) The video controller notifies the PHC 10 in real time of the paper feeding / discharging of the main body and the print start state. With this information, the PHC 10 grasps all the paper transport information. (4) In the transport status area, by using the memory for 40 sheets in a ring shape, the latest 40 sheets of information are always shared by the video controller 9 and the PHC 10.

Command & Status Management Area: (1) The video controller 9 writes command data in the command area, and P is set by the condition flag.
Notify the HC10. (2) The PHV 10 recognizes the arrival of a command by the condition flag, performs processing, writes the status data in the status area, and notifies the video controller by the condition flag. (3) The command is always written from the video controller side. (4) As the status, the PHC 10 always returns a status corresponding to the command. (5) Using the above command & status, connection information (CONFIGURATION) at device startup,
Acquires detailed jam information and detailed failure information when a jam occurs.

Tables 1 and 2 of the attached sheet show examples of use in the transportation status management area. Tables 1 and 2 show an example in which the double-sided unit 3 is used to carry 8 sheets and 16 images.
Item No. in this memory. And their names and their outlines are explained in the attached Tables 3 to 6. In the table, C in the data direction indicates the video controller 9, and 0C indicates the PHC 10.

How to read Tables 1 and 2 will be described. When attempting to print, the video controller 9 first designates an image number, paper number, copy number, JOB number, and paper size in Item Nos. 1 to 6 in the condition designation area. For one page, start from the physical address 000h. When the execution flag is set to 1, it means that the execution is started as soon as the condition is satisfied.

Next, the printing conditions are specified, and the paper feeding condition, that is, the paper feeding source is designated. Next, specify the discharge conditions. For both sides of the paper ejection unit, the paper is the first page of front printing (front side)
Means that after printing, the second page (reverse side) is printed by inserting it in the duplex unit, reversing it, and re-feeding it.

Items up to Item No. 15 are items designated by the video controller 9. When the designation is made up to this point, the paper handling controller 10 issues an instruction to the sheet feeding deck 6 and the finisher 7 according to the designated items. If the paper feeding / discharging device is ready, the print permission flag is set to 00h (OK).
To

Upon seeing this, the video controller 9 issues a print signal / PRNT to the engine controller. This signal is also checked by the CPU 13 to confirm that the printing operation has started. Furthermore, the video controller 9
Write operation start 1h to temNo20 print state.

When paper feed is started from the paper feed deck side when the paper feed is started, the PHC 10 has Item No. 19 in the memory 14.
In the case of paper feeding on the main body side, the video controller writes the paper feeding execution 2h in the main body in the same address.

As a result, even if the paper is managed by the PHC, the PH
What is the current situation with paper feeding in the main body that C does not manage?
Both the HC and the video controller are visible. This is an advantage of sharing information by memory. Regarding the paper discharge, the paper discharge in the main body 1 is detected by the sensor 20 at the exit of the fixing device 22 as shown in FIG.
The image forming apparatus 8 outputs the signal. The discharge of the finisher 7 is detected by the exit sensors 21a to 21c for each page.

When the paper discharge is completed, the PHC 10 judges the paper discharge inside the main body and the finisher paper discharge, and the Item 14 of the memory 14 is judged.
Data is written in No. 20 paper discharge state. Insulator V
The PHC 10 judges the PDLV signal of the IDE I / F. In the finisher discharge, the PHC 10 judges the discharge completion signal from the finisher 7.

When the paper discharge is completed, the PHC 10 writes END into the ItemNo 21 of the memory 14. ST in the table
ART indicates that the operation has already started, and 0 indicates that the operation has not started. When the paper discharge operation is completed, the PHC stores the Ite in the memory 14.
Write OK (01h) to the RAM release of mNo17.
This information is written for each image number, that is, for each page.

This indicates that the image memory of the written pages stored in the video controller 9 may be erased because it is no longer necessary for each page for reprinting when a print abnormality occurs. The video controller 9 erases the memory after confirming that there is no jam or print error in the status. Without this information, the video controller 9 must store the image information forever and cannot effectively use the memory.

In the present invention, the RAM release timing for each page can always be known from the table in the memory 14. In the present invention, although there is a principle that the memory 14 is used in order of advancing the address in page order, the reading / writing procedure of each item may be random.

Therefore, all pages can be checked in real time for the printing status and the progress of the pages already designated. This information can be sent to the host computer side or displayed on the main body display unit 2 via the video controller. As a result, the user can easily know the print states of all the sheets of paper in the image forming apparatus.

(Second Embodiment) In the first embodiment, the information exchange method via the PHC and the memory 14 of the video controller has been described. Next, an example of the paper transport control that can be realized by the PHC referring to the paper handling schedule of the memory 14 will be described.

In the present invention, the paper handling controller 10 receives in advance from the video controller a schedule of sheets of paper to be printed.
This means that when the paper conveyance distance from the paper feed deck 6 placed under the main body 1 to the main body 1 is long, the paper can be delivered early in anticipation of the time.

For example, in Table 1, image No. 8 is paper feed No. 1
Unit (paper feed deck 6 in this embodiment), then double-sided,
Next is paper feed No. 1 again. In such a case, first feed the paper from the paper feed deck. This paper is stopped at the entrance of the main body 1. If the paper transport path is long and two sheets of paper can exist in the transport path, another sheet will be immediately fed from the paper feed deck.

Since the paper handling controller 10 knows the paper feed schedule in advance, such advance paper feed can be performed.

The procedure for preceding feeding of the PHC 10 will be described with reference to a flowchart. In step S101, the print state of the memory 14 is searched to find the latest print start page.
In step S102, the paper feed unit designation of the page whose print state is FFh (start state) is checked. If the paper feed deck is designated in step S103, step S1
In 04, it is checked whether the paper feeding deck is performing the paper feeding operation.
In this case, in step S105, the paper feed preparation state is entered, and the paper feed is executed after a predetermined time. If NO, step S10
At 6, the paper is fed immediately. In step S107,
Check the paper feed unit on the next page, and go to step S
Return to 103.

(Third Embodiment) Next, an embodiment for further improving the efficiency of the preceding paper feeding will be described. This is a case where the paper feed deck has a plurality of paper feed units. A description will be given according to the flowchart of FIG. This is also used at the time of preceding paper feeding in the second embodiment. In step S201, a search is made to see if there are paper feed sources of the same size (the paper size of each paper feed source is checked and stored in advance by the PHC 10). If there is, step S20
In step 2, a paper feed source with a short transportation time is selected. Since the feeding time of each paper source is stored in the paper feeding device, the PHC10
Read in advance via the interface line 12.

In step S203, the presence / absence of paper in the earlier paper feed source is checked, and if there is, paper is fed in step S204. If there is no paper in step S203, step S203
In 205, the slow paper source is selected, and in step S206,
The presence or absence of paper is detected, and if there is, paper is fed in step S207.

In step S201, if there is no paper source of the same size, the paper source can be specified. Therefore, in step S208,
If the presence / absence of paper is checked, the paper is fed in step S204, and if not, the absence of paper is displayed on the display unit 2 in step S209. However, the display timing is set to be just before the sheet feeding operation is actually started with the sheet feeding source. This is because the user is confused if the pre-feeding is displayed too early.

In this way, the paper feed source can be selected by using the time margin of the preceding paper feed, and the fastest throughput can be obtained. This is also possible because the PHC 10 can read the paper feed schedule in the memory first. Also,
Even when the paper source is switched to another paper source when there is no paper, it can be executed with a time margin in advance.

(Fourth Embodiment) In the first embodiment, the memory 1
Although reading and writing from and to 4 are random, while the designated items are being designated, for example, the feeding condition and the discharging condition are set to the video controller 4
If the PHC reads and executes it while being specified, the operation may be partially left unspecified.

The countermeasure will be described. The memory 14ItemNo1 in Table 1 and an execution flag are provided. This definition is shown in Table 3. In the detailed data contents of Table 3, the designation "2, ... Writing and discharging paper condition data but not operating" is given.

That is, when writing the designated items in the memory 14, immediately before that, the data of 02h is written in the execution flag of the corresponding page, and if the designated items are written, the PHC
10 does not start operation. Therefore, PHC remains partially unspecified
Does not move.

As another means, it is possible to prevent the PHC 10 from operating until an execution instruction is issued to the execution flag. This is the data content of the execution flag data in Table 3,
"1. Perform normal operation according to data". That is, the PHC 10 does not start operating until 01h data is written in the execution flag.

The operation of the PHC1 at this time is shown in the flowchart of FIG. In step S301, Item of the memory 14
The CPU 13 of the PHC reads the mNo1 execution flag and sets it to 0.
Check if it is 2h. If YES, pass without doing anything.

If NO, it is checked in step S302 whether or not the execution flag is 01h, and if YES, the specified conditions such as the paper feed condition, the paper discharge condition and the print condition designation are read in step S303, and in step S304. Starts the operation according to the specification.

If NO in step S302, in step S305, another content 03h of the execution flag is set.
Perform ~ 06h analysis. In this embodiment, 02h is checked, but it is also possible to start the operation by checking only 01h.

[0058]

【The invention's effect】

(1) By providing a shared memory in the building of the image information control device and the paper conveyance control device and exchanging information, the paper conveyance control device can manage the schedule of the paper conveyance control device. Therefore, it is possible to feed a plurality of sheets in advance. Therefore, even if a paper feeding device with a long conveyance path is combined, printing is possible without reducing throughput. (2) The advance paper feeding allows a time margin, and it becomes possible to select the most suitable paper feeding source and obtain the fastest throughput. (3) The paper transport control device professionally controls the paper,
By notifying the image information control device of the control timing, the image information control device is released from the paper conveyance control, and the image information processing can be speeded up. (4) The paper conveyance control device writes all movements of all papers in the image forming apparatus to the shared random access memory, and the image information control device displays the same to the user so that the user can make the papers in the image forming apparatus. You can learn to pick up the movement of. (5) The execution flag is provided in the shared memory to indicate that the image information control device is writing the specified condition, or the operation start instruction is written to the memory so that the paper conveyance control device starts the operation while the specified condition is being written. It can be prevented. This is very effective in preventing troubles by allowing random access by sharing the memory. (6) By detecting the end of paper conveyance for each page, writing the result in the page to the random access memory and notifying the result, and releasing the image memory for each page,
Image memory can be used efficiently.

[Table 1]

[Table 2]

[Table 3]

[Table 4]

[Table 5]

[Table 6]

[Brief description of drawings]

FIG. 1 is a circuit block diagram showing a first embodiment of the present invention.

FIG. 2 is an overall view of the image forming apparatus.

FIG. 3 is a layout view of a main control device of the present invention.

FIG. 4 is a flowchart of a second embodiment.

FIG. 5 is a flowchart of a third embodiment.

FIG. 6 is a flowchart of a fourth embodiment.

[Explanation of symbols]

 1 Main Body 2 Display Section 3 Double-sided Unit 4 Envelope Feeder 6 Paper Feeding Deck 7 Finisher 8 Image Forming Control Device 9 Image Information Control Device (Video Controller) 10 Paper Transport Control Device (PHC) 13 CPU of PHC 14 Dual Port Memory 15 of PHC ROM

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinichiro Maekawa 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Yutaka Tokura 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Incorporated (72) Inventor Yoichi Toyokura 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Satoshi Egawa 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. ( 72) Inventor Shigeru Ueda 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (14)

[Claims] 1. An image forming apparatus, an image information control apparatus for controlling image information, an image forming control apparatus for controlling an image forming operation, the image information control apparatus, the image forming control apparatus, and a paper conveyance control. An image forming apparatus, which is provided with a paper conveyance control device that specializes in: and a random access memory shared between the paper conveyance control device and the image information control device. 2. The image forming apparatus according to claim 1,
An image forming apparatus characterized in that a random access memory stores a management table relating to paper feeding, paper discharging, and printing conditions of the image forming apparatus. 3. The image forming apparatus according to claim 1,
An image forming apparatus, wherein a portion for storing print permission information is provided in a random access memory, and the print permission information is writable only by a sheet conveyance control device. 4. The image forming apparatus according to claim 1,
An image forming apparatus characterized in that a sheet conveyance control device manages a schedule of a printing operation of the image forming device by exchanging information between the image information control device and each sheet feeding / discharging device. 5. The image forming apparatus according to claim 1,
The paper conveyance control device controls the paper feed / ejection device according to the paper feed / ejection information specified in advance in the random access memory from the image information control device and writes the status of each paper feed / ejection device in the random access memory. A characteristic image forming apparatus. 6. The image forming apparatus according to claim 1,
When the image information control device receives the image information to be printed from the host computer or the print command, the image information control device notifies the paper feed / discharge information to the paper transport control device before the printing operation. An image forming apparatus characterized in that each paper feeding / discharging device is instructed to perform a preparatory operation in advance based on the information. 7. The image forming apparatus according to claim 6,
An image forming apparatus characterized in that when a paper-out condition is detected during pre-feeding, an alternative paper-feed source is selected and the paper is fed. 8. The image forming apparatus according to claim 1,
When a plurality of paper feed sources are provided, the paper conveyance control device selects a paper feed source that realizes the fastest throughput within a range in which the printing order instructed by the image information control device can be observed. . 9. The image forming apparatus according to claim 1,
The image forming apparatus is characterized in that the random access memory is a dual port memory having an arbitration function. 10. The image forming apparatus according to claim 5, wherein, when the image information control device writes the designation condition in the random access memory, immediately before that, information indicating designation is written in the memory, and while the information is being output. Is an image forming apparatus that prohibits the sheet conveyance control device from operating based on the specified condition. 11. The image forming apparatus according to claim 5, wherein the random access type transport control device is prohibited from operating based on the specified condition until the image information control device writes an operation start instruction in the random access memory. An image forming apparatus characterized by the above. 12. The image forming apparatus according to claim 1, wherein the paper conveyance control device has a portion for storing paper conveyance end information, and manages the image information by the paper conveyance end information. . 13. The image forming apparatus according to claim 12, further comprising means for notifying the erasability of the image memory for each page of the image by the sheet conveyance end information. 14. The image forming apparatus according to claim 13, further comprising writing means for writing notification information to a specific address in the random access memory as means for notifying that the image memory can be erased.