Abstract:
A display control device for controlling a display of a display device responding to display processing from a plurality of processing units. A display controlling program controls the display device in response to at least one processing unit. The display controlling program receives a request from one processing unit to acquire one of predefined display areas, and determines whether to provide an authorization to acquire one of a plurality of predefined display areas in response to an acquisition request from the one processing unit. When a plurality of requests to acquire the same one of predefined display areas from a plurality of processing units are received, authorization is provided to a single processing unit that made one of the requests to acquire the same one of predefined display areas. The display device is instructed by a processor, based on the display controlling program. A memory, connected to the processor, stores the display controlling program. When an acquisition request for the same one of predefined display areas is received, the processor instructs the display device based on the display controlling program.

Description:
REFERENCE TO RELATED APPLICATIONS 
   This application is a divisional application of pending U.S. patent application Ser. No. 10/749,589 filed on Jan. 2, 2004, now U.S. Pat. No. 7,221,362 which is a divisional of U.S. patent application Ser. No. 09/320,543 filed May 27, 1999, that issued as U.S. Pat. No. 6,710,789. 

   All the disclosure in Japanese Patent Applications HEI 10-147815 “Display control device and method” (filed on May 28, 1998) and HEI 11-133419 “Display control device and method” (filed on May 14, 1999), including specifications, claims, drawings and abstract, are hereby incorporated herein reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a technology for control display on a screen by a plurality of processing units (tasks and applications), and more particularly to an allocation of the display area. 
   2. Description of the Related Art 
   When a plurality of applications display on one screen, a window system, such as X-Window System, has been used. In these window systems, each application displays acquiring the respective window (multi-window). 
   Japanese Laid-Open Patent Application HEI4-274289 discloses a device which groups windows acquired by each application, and displays or does not display in group units. 
   Also in accordance with Japanese Patent Laid-Open No. 1-100662, when contents displayed on a plurality of windows are inter-related, these plurality of windows are simultaneously displayed so that the user can easily understand the display contents. 
   However, with the conventional display based on a multi-window, what application displays on what display area basically depends on the application. Therefore it is possible for an application to display a window which overlaps with the window displayed by another application. When such a problem occurs, the user must change the position of the window which is overlapped by another window in order to view the display of the window, which is troublesome. 
   In satellite broadcasting TV, where users need not change the positions of windows, different applications must be used to prevent the overlapping display of windows. For such devices, a conventional window system cannot be used. 
   In accordance with the Japanese Laid-Open Patent Application HEI4-274289, multiple windows specified by an application are grouped so as to improve the operability of each window, but the handling of overlapping of windows depends on the application. In other words, an undesired display of multi-windows is inevitable, and the above mentioned problems are not solved. 
   In accordance with the Japanese Laid-Open Patent Application HEI1-100662, the handling of overlapping windows also depends on the application, where an undesired display of multi-windows is still inevitable, and the above mentioned problems are not solved. 
   SUMMARY OF THE INVENTION 
   With the foregoing in view, it is an object of the present invention to provide a device and a method which can display data in an appropriate display area for each processing unit, such as an application, according to the applied equipment. 
   (1) A display control device and method according to the present invention defines a plurality of display areas in the display device, and when a display area acquisition request is received from each processing unit, it is decided whether to use the requested display area, and the processing unit which is allowed to use the display area can display data there. By defining display areas in advance, and by allowing the use of each display area, without leaving control to each processing unit, an appropriate display for each processing unit according to the applied equipment becomes possible. Also inappropriate display is prevented. 
   (2) When display area acquisition requests are received from a plurality of processing units, the display control device according to the present invention judges whether the display areas subject to respective acquisition requests can coexist, and if the plurality of processing units are requesting acquisition of display areas which cannot coexist, use is allowed to one of the processing units. As a consequence, a plurality of display processing which cannot coexist can be prevented and appropriate display becomes possible. 
   (3) When the display areas subject to respective acquisition requests all or partially overlap, the display control device according to the present invention judges as coexistence impossible. As a consequence, it is possible to control such that displays by a plurality of processing units do not overlap. 
   (4) When a plurality of processing units request acquisition of one display area, the display control device according to the present invention judges as coexistence impossible. As a consequence, it is possible to control such that two or more processing units are not allowed to use one display area. 
   (5) When a plurality of display areas subject to respective acquisition requests partially overlap, the display control device according to the present invention judges as coexistence possible. As a consequence, it is possible to control such that a partial overlapping display is allowed. 
   (6) When a display processing is executed for a plurality of display areas which can coexist with partial overlapping portions, the display control device in accordance with the present invention displays assigning priority to an area having a higher priority in the overlapped portion. As a consequence, it is possible to control such that the overlapped portion is displayed according to priority. 
   (7) The display control device in accordance with the present invention judges the possibility of coexistence based on the coexistence relationship information where the possibility of coexistence of a plurality of display areas has been defined in advance. As a consequence, it is possible to quickly judge whether the requested display areas can coexist. 
   (8) When an acquisition request for a display area which cannot coexist is received, the display control device in accordance with the present invention allows use to the processing unit which sent the request first. As a consequence, it is possible to assign priority to the display by the processing unit which sent the display request first. 
   (9) When an acquisition request for a display area which cannot coexist is received, the display control device in accordance with the present invention allows use to the processing unit which has the higher priority. As a consequence, it is possible to display data which is most urgent, such as a warning display. 
   (10) When an acquisition request for a display area which cannot coexist is received, the display control device in accordance with the present invention allows use to the processing unit which requests the area having the highest priority. As a consequence, areas in a display can be different depending on the urgency. 
   (11)-(14) The display control device according to the present invention stores a processing unit which requested acquisition but was not allowed use of the display area as an acquisition waiting, and allows use of the display area when allowance is possible. As a consequence, use is allowed sequentially for display area acquisition requests. Each processing unit does not have to request acquisition again. If use is allowed considering the order of received requests, priority given to the processing units, and priority given to the display areas, then use can be allowed according to sequence in the order considering such priorities. 
   (15) When a request for a display area which cannot coexist is received, the display control device according to the present invention changes the display area requested by one or more processing units so as to allow use as a plurality of display areas which can coexist. As a consequence, a plurality of displays can coexist as much as possible while maintaining an appropriate display by a plurality of display areas. 
   (16) When a request for a display area which cannot coexist is received, the display control device according to the present invention changes the display area based on dependency relationship information defining the changes of the display area to make coexistence possible. As a consequence, the display area can be quickly changed so as to make coexistence possible. 
   (17) (21) The display control device according to the present invention defines the processing units which are allowed use for each display area as acquisition right information, and when a display area acquisition request is received from each processing unit, the display control device refers to the acquisition right information and decides whether use of the display area is allowed for each processing unit. As a consequence, it is possible to control by allocating processing units for each display area. 
   (18) The display control device according to the present invention does not allow two or more processing units simultaneous use of one display area. As a consequence, it is possible to control so as to correlate a display area and a processing unit on a one-to-one basis. 
   (19) (20) The display control device according to the present invention allows two or more processing units simultaneous use of one display area. As a consequence, it is possible to control so as to allow two or more processing units to use one display area. 
   (22) (23) When the processing unit which requested the display area is actually not in a state to display on the display area, or is not in a state to execute processing related to the display processing, the display control device according to the present invention does not allow the processing unit to use the display area even if the display area requested by the processing unit can coexist with display areas requested by other processing units. As a consequence, to make display efficient, use is not allowed for a processing unit which cannot actually execute display processing and processing related to display. 
   (24) The display control device according to the present invention also has display processing supervisory means, wherein when each processing unit executes display processing for each display area, it is supervised whether the display processing is by a processing unit which is allowed use of the display area. As a consequence, execution of invalid display processing can be supervised. 
   (25) (26) The display control device according to the present invention assigns a key to the processing unit when use of a display area is allowed, and the display processing supervisory means supervises by judging whether the key shown by the processing unit is the correct key. As a consequence, invalid display processing can be easily supervised. By assigning a different key each time, invalid display processing using an old key can be prevented. 
   (27) When a processing unit attempted to execute display processing for a display area which is not allowed use is discovered, the display control device according to the present invention executes processing to disable the display processing by the processing unit. As a consequence, a processing unit which attempted invalid display processing can be removed. 
   In the present invention, “processing unit” refers to a set of processings to obtain a certain result. One processing unit may be comprised of one task, but may include two or more tasks. 
   The concept “case when all the display areas subject to the acquisition requests overlap” includes the case when two or more acquisition requests are received for the same display area. 
   “Cannot coexist” is the case when displaying in a plurality of display areas is not desirable. Depending on the equipment to which the display control device is applied to or depending on the status, a plurality of display areas may not be able to coexist if a part of the display area overlaps, or may be able to coexist even if overlapping exists in a predetermined allowable range. There is also a case when a specific display area can coexist even if it overlaps with another display area. 
   The concept “resource used by a processing unit” includes not only hardware but also software, such as data and programs. 
   The concept “display area storage means” refers to a means for storing the definitions of display areas, and includes means for substantially defining display areas, regardless table format or descriptions in a program. In the embodiments, the display area definition table in  FIG. 6  falls under this concept. 
   The concept “display area management means” refers to a means for deciding whether use of the area is allowed at least when a display area acquisition request is received. In the embodiments, the display control program shown in e.g.  FIG. 8  falls under this concept. 
   The concept “computer” refers to a device which executes processing according to a program, and includes a personal computer, and a CPU and MPU built-in to such equipment as a TV. 
   “Recording medium where a program is recorded” is such a recording medium as ROM, RAM, a flexible disk, CD-ROM, memory card and hard disk, where a program is recorded. This concept includes not only such a recording medium as a hard disk which is connected to a CPU and with which the recorded program is directly executed, but also such a recording medium as CD-ROM which records a program to be executed after installing it on a hard disk. A program here includes not only a program which can be directly executed, but also a source format program, compressed program and enciphered program. 
   Features, other objectives, applications and effects of the present invention will be clarified by referring to the embodiments and drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a drawing depicting an embodiment of a display control device in accordance with the basic concept of the present invention; 
       FIG. 2  is a drawing depicting a general configuration of the display control device  2  according to the first embodiment; 
       FIG. 3  is a drawing depicting a hardware configuration when the display control device in  FIG. 2  is applied to a digital broadcasting receiver; 
       FIG. 4  is a drawing depicting details of an AV decoder; 
       FIG. 5  is a drawing depicting an example of defining a display area; 
       FIG. 6  is a drawing showing content of a display area definition table; 
       FIG. 7  is a drawing showing content of an acquisition status storage table; 
       FIG. 8  is a flow chart showing an acquisition request processing portion of a display control program in accordance with the first embodiment; 
       FIG. 9  is an example of a screen display on TV set  36 ; 
       FIG. 10  is an example of a screen display by a plurality of applications; 
       FIG. 11  is a flow chart showing a release request processing portion of the display control program in accordance with the first embodiment; 
       FIG. 12  is a drawing depicting a basic hardware configuration of the display control device according to the embodiment of the present invention; 
       FIG. 13  is a drawing depicting a general configuration of the display control device  2  according to the second embodiment; 
       FIG. 14  is a drawing depicting a display area definition example; 
       FIG. 15  is a drawing showing content of a display area definition table; 
       FIG. 16  is a drawing showing content of an acquisition status storage table; 
       FIG. 17  is a drawing showing content of a coexistence relationship table; 
       FIG. 18  is a flow chart showing an acquisition request processing portion of a display control program in accordance with the second embodiment; 
       FIG. 19  is an example of a display of a program schedule on screen; 
       FIG. 20  is a flow chart showing a supervisory processing portion of the display control program in accordance with the second embodiment; 
       FIG. 21  is an example of a display of a program schedule and weather forecast; 
       FIG. 22  is a flow chart showing a supervisory processing portion of the display control program in accordance with the second embodiment; 
       FIG. 23  is a drawing showing content of a display area priority table; 
       FIG. 24  is a flow chart showing an acquisition request processing portion of a display control program in accordance with the third embodiment; 
       FIG. 25  is a display area definition example on a screen; 
       FIG. 26  is a drawing showing a coexistence relationship table; 
       FIG. 27  is a drawing showing a display area priority table; 
       FIG. 28  is a flow chart of a program for display processing; 
       FIG. 29  is a drawing depicting an example of a screen when a display area for urgent display having high priority is created; 
       FIG. 30  is a drawing showing content of a processing unit priority table; 
       FIG. 31  is a flow chart showing an acquisition request processing of a display control program in accordance with the fourth embodiment; 
       FIG. 32  is a drawing depicting a general configuration of the display control device  2  according to the fifth embodiment; 
       FIG. 33  is a drawing showing content of a dependency relationship table; 
       FIG. 34  is a flow chart showing an acquisition request processing portion of a display control program in accordance with the fifth embodiment; 
       FIG. 35  is a drawing showing content of an acquisition status storage table; 
       FIG. 36  is a drawing depicting a general configuration of the display control device  2  according to the sixth embodiment; 
       FIG. 37  is a drawing showing content of an available resource table; 
       FIG. 38  is a drawing showing content of a use resource table; 
       FIG. 39  is a flow chart showing an acquisition request processing portion of a display control program in accordance with the sixth embodiment; 
       FIG. 40  is an example of a display on a screen; 
       FIG. 41  is a flow chart showing an acquisition request processing portion of a display control program in accordance with the seventh embodiment; 
       FIG. 42  is a flow chart showing a release request processing portion of the display control program in accordance with the seventh embodiment; 
       FIG. 43  is a drawing showing an example of content stored in an acquisition waiting table; 
       FIG. 44  is a flow chart showing a portion of a processing acquisition request in waiting status of the display control program in accordance with the seventh embodiment; 
       FIG. 45  is a drawing depicting a general configuration of a display control device according to the eighth embodiment; 
       FIG. 46  is an example of a display area definition example; 
       FIG. 47  is a drawing showing a display area definition table; 
       FIG. 48  is a drawing showing an acquisition right information table; 
       FIG. 49  is a flow chart showing an acquisition request processing portion of a display control program in accordance with the eighth embodiment; 
       FIG. 50  is a drawing showing an acquisition right information table; 
       FIG. 51  is a drawing showing an acquisition right information table where the upper limit of the number of usable tasks is limited; 
       FIG. 52  is a flow chart showing an acquisition request processing portion of the display control program; and 
       FIG. 53  is a drawing showing an acquisition status storage table. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Table of Contents 
   1. Display Control Device in Accordance with the Basic Concept of the Invention 
   2. First Embodiment 
   
       
       
         
           2.1 General Configuration 
           2.2 Example of Application to Digital Broadcasting Receiver
 
3. Second Embodiment
 
           3.1 General Configuration 
           3.2 Embodiment Applied to a Digital Broadcasting Receiver 
           3.3 Handling of Task Attempted Invalid Processing
 
4. Third Embodiment
 
           4.1 Example when Overlapped Areas are not Allowed to Coexist 
           4.2 Example when Overlapped Areas are Allowed to Coexist
 
5. Fourth Embodiment
 
6. Fifth Embodiment
 
7. Sixth Embodiment
 
8. Seventh Embodiment
 
9. Other Embodiments
 
10. Eighth Embodiments
 
           10.1 General Configuration 
           10.2 Example when One Processing Unit is Allocated to One Display Area 
           10.3 Example when a Plurality of Processing Units are Allocated to One Display Area 
           10.4 Example when a Plurality of Tasks are Allowed to use One Display Area 
         
       
     
  
   1. Display Control Device in Accordance with the Basic Concept of the Invention 
     FIG. 1  shows a general configuration of the display control device  2  as an embodiment of the basic concept of the present invention. The display control device  2  comprises display area management means  4  and display area storage means  6 . The display area storage means  6  stores definitions of a plurality of display areas which are set on a screen of the display device  8 . To the display area management means  4 , a display area acquisition request for displaying is sent from a plurality of processing units R 1 -Rn. The display area management means  4  decides whether use of the display area is allowed for each processing unit, considering the relationship of the plurality of display areas requested from each processing unit R 1 -Rn. Each processing unit R 1 -Rn executes display processing for the display areas for which use is allowed. 
   In this way, after each processing unit R 1 -Rn sends a display area acquisition request, the display area management means  4  notifies each processing unit R 1 -Rn whether use is allowed. As a consequence, display on a plurality of areas by each processing unit R 1 -Rn can be appropriately controlled. 
   2. First Embodiment 
   2.1 General Configuration 
     FIG. 2  shows a general configuration of a display control device  2  as an embodiment of the present invention. In this embodiment, acquisition status storage means  10  connected to the display area management means  4  is disposed. The acquisition status storage means  10  stores the acquisition status correlating a display area and tasks T 1 -Tn which are processing units which acquired the display area. When a display area acquisition request is received from one of the tasks T 1 -Tn, the display area management means  4  judges whether the display area has been acquired by another task based on the storage content of the acquisition status storage means  10 . If the display area has been acquired by another task, the task is not allowed to use the display area. If the display area has not been acquired by another task, the task is allowed to use the display area. 
   2.2 Example of Application to Digital Broadcasting Receiver 
     FIG. 3  shows a hardware configuration when the display control device shown in  FIG. 2  is applied to a digital broadcasting receiver. In this example, each function shown in  FIG. 2  is implemented by CPU  12 . 
   In satellite digital broadcasting and ground wave digital broadcasting, a plurality of services are multiplexed and sent as a transport stream. The radio wave captured by an antenna  38  is sent to a tuner  30 . The tuner  30  selects and demodulates the transport stream carrying the desired service according to the control of the CPU  12 . The demodulated transport stream is sent to a transport decoder (TS decoder)  32 . The transport decoder  32  selects the desired service from the transport stream according to the control of the CPU  12 , and outputs it to an audio video decoder (AV decoder)  34 . The AV decoder receives the data, decompresses the compressed data, carries out D/A conversion, and outputs video composite signals (e.g. NTSC signals). 
     FIG. 4  shows details of the AV decoder  34 . The decompression circuit  41  decompresses the output from the TS decoder  32  and sends it to a video RAM  42 . In data broadcasting, display content is controlled by overwriting the V-RAM  42  from the CPU  12 . A composite signal generation circuit  44  converts the content of the V-RAM  42  from digital to analog so as to convert to video composite signals. 
   Referring to  FIG. 3 , A TV set  36 , which is a display device, receives the video composite signals and outputs images and sound. A modem  17 , which is a communication control circuit, is used for communication with the outside via telephone lines. 
   The CPU  12  controls the above mentioned receive processing according to a station selection application (program) recorded in a ROM  16 . The CPU  12  judges which service is to be received based on the input by the user, which is input from an operation input section  40 . The operation input section  40  may be a receiving part of a remote controller (not illustrated) or operation buttons disposed on the receiver main body. 
   In the ROM  16 , such tasks as a caption application, a program schedule application, a program reservation application, a data receiving application, and a system setting application have been recorded, in addition to the station selection application. Also in the ROM  16 , a display control program and a display area definition table have been recorded. A work memory  14  functions as a work area of the CPU  12 . 
     FIG. 5  shows a display area definition example on the screen of the TV set  36 . In this embodiment, each display area E 1 -E 3  is defined so as not to overlap with each other. In the ROM  16 , a display area definition table (display area storage means) for indicating the definitions of each display area E 1 -E 3  has been recorded, as  FIG. 6  shows. In this embodiment, the coordinates are indicated by display dots, where the upper left corner of the screen is (0, 0), the lateral direction is X and the longitudinal direction is Y. The lower right corner is (679, 339). 
   The work memory  14  has an acquisition status storage table for recording acquisition status correlating each area E 1 -E 3  and tasks which acquired each area, as  FIG. 7A  shows. 
     FIG. 8  shows a flow chart of an acquisition request processing portion (display area management means) of the display control program recorded in the ROM  16 . Now, with reference to this flow chart, the case when a data receiving application (task T 1 ) executes display processing for the display area E 2 , will be described. The data receiving application is an application for receiving data broadcasting (e.g. weather forecasting data) and executing display based on this data. At first the data receiving application sends a request to acquire the display area E 2  to the CPU  12 . The CPU  12  receives this request and starts the display control program shown in  FIG. 8  (Step S 201 ). 
   Then the CPU  12  reads the display task storage table in the work memory  14 , and acquires a use status of the requested display area E 2  (Step S 202 ). Based on the obtained status, the CPU  12  judges whether the requested display area E 2  has been acquired by another application (task) (Step S 203 ). Here, the display area E 2  has not been acquired by any other task, as  FIG. 7A  shows. Therefore the processing advances to Step S 204 . 
   In Step S 204 , the data receiving application (task T 1 ) is stored correlating to the display area E 2  of the display task storage table.  FIG. 7B  shows the display task storage table after storing the task T 1 . 
   Then the CPU  12  notifies the data receiving application (task T 1 ) to allow use of the requested display area E 2 . In this way, the data receiving application (task  1 ) acquires a display right for the display area E 2 . The data receiving application which acquired the display area E 2  executes display processing for the area. In other words, according to the data receiving application, the CPU  12  overwrites the V-RAM  42  based on the received content of the data broadcasting, and displays data broadcasting, as shown in  FIG. 9 . 
   A case when a program schedule application (task T 3 ) requests acquisition of the display area E 2  again in the above status will be explained. The program schedule application is an application to receive and display an electronic program schedule (EPG). In this case as well, the display control program shown in  FIG. 8  is started by the acquisition request from the program schedule application (task T 3 ) (Step S 201 ). The CPU  12  recognizes that the requested display area E 2  has already been acquired by the data receiving application (task  1 ) based on the acquisition status storage table (see  FIG. 7B ). Therefore the processing advances from Step S 203  to S 207 . In this embodiment, two tasks are not allowed to use the same display area, so the CPU  12  notifies the program schedule application (task T 3 ) that the display area E 2  cannot be acquired (Step S 207 ). The program schedule application (task T 3 ) receives this message, and selects whether to wait until the display area E 2  is released or to request acquisition of another display area, or to give up display at this time. 
     FIG. 10  shows an example of the screen display when the program schedule application requests to acquire a display area E 3  and a program reservation application requests to acquire a display area E 1  in the above status. According to this embodiment, each application is allowed use of a display area such that disorder is not caused by e.g. overlapping of a display by each application, therefore display by a plurality of applications can be appropriately executed, as shown in  FIG. 10 . 
   When the above data receiving application (task T 1 ) which acquired the display area E 2  ends the display processing on the display area, the data receiving application (task T 1 ) requests release of the display area E 2  to the CPU  12 .  FIG. 11  shows a flow chart of a processing program (release request processing) in this case. The CPU  12  receives the release request and starts processing shown in  FIG. 11  (Step S 301 ). At first, the CPU  12  obtains the working status of the display area E 2 , for which release was requested, from the acquisition status storage table (Step S 302 ). Since the content of the acquisition status storage table at this point is as shown in  FIG. 7B , the CPU  12  recognizes that the display area E 2  has been acquired by the data receiving application (task T 1 ). 
   Then the CPU  12  judges whether the task which requested the release has actually acquired the display area. This judgment is made based on whether the task which requested the release of the display area matches the task which has acquired the display area (step S 303 ). This judgment is made to prevent a task which has not acquired the display area from requesting an incorrect release. When the tasks do not match in Step S 303 , the display area is not released, and failure of the release is notified to the task which requested the release (Step S 307 ). 
   Since the data receiving application (task T 1 ) which requested release of the display area E 2  has actually acquired the display area E 2  here, processing advances to Step S 304 . In Step S 304 , the task T 1  which was stored correlating to the display area E 2  in the acquisition status storage table is deleted. As a result, the content of the acquisition status storage table becomes the status shown in  FIG. 7A . Therefore if a new acquisition request for the display area E 2  is received, use can be allowed. 
   After deleting the task from the acquisition status storage table, the CPU  12  notifies the data receiving application (task T 1 ) that the area is released (Step S 305 ). 
   In the above embodiment, when display area acquisition requests are received from a plurality of applications (tasks), it is judged whether the display areas subject to the acquisition request are the same areas, and if they are, then the task which requested the acquisition first is allowed use of the display area. In other words, if a plurality of tasks request acquisition for the same display area, it is judged that coexistence is impossible, and if the tasks request acquisition for different areas, then it is judged that coexistence is possible. 
   3. Second Embodiment 
   3.1 General Configuration 
     FIG. 13  shows a general configuration of a display control device  2  according to the second embodiment of the present invention. In this embodiment, coexistence relationship storage means  20  is disposed. The coexistence relationship storage means  20  stores the coexistence relationship information to indicate whether a plurality of display areas can coexist. The display area management means  4  judges whether the display areas desired by the acquisition requests from each processing unit R 1 -Rn can coexist, based on the coexistence relationship information of the coexistence relationship storage means  20 . If coexistence is impossible, the processing unit which requested acquisition first is allowed use of the display area. 
   A display processing supervisory means  22  judges whether each display processing by each processing unit R 1 -Rn is for a display area where use of each display processing is allowed. If the display processing is for a display area where use is not allowed, the display processing is not accepted. 
   In the first embodiment, one task corresponds to one processing unit. In the second embodiment, however, the case where one processing unit R 1  includes a plurality of tasks T 11 -T 1   m  will be explained. For example, a program schedule application as a processing unit includes three tasks, that is, 1) task  1 , which sends operation input from an operation input section  40  to task  2  or task  3  depending on the situation, 2) task  2  which displays the program schedule on screen, and 3), task  3  which displays the details of the program on screen. 
   A display area acquisition request is sent from each processing unit R 1 -Rn, and use is allowed for each processing unit R 1 -Rn. An acquisition request may be sent from each processing unit R 1 -Rn independently, or be sent from a specific task of each processing unit R 1 -Rn as a representative of the processing unit. The latter case will be explained below. 
   3.2 Embodiment Applied to a Digital Broadcasting Receiver 
   The case when the display control device  2  in  FIG. 13  is applied to a digital broadcasting receiver will be explained. The hardware configuration is the same as in  FIG. 3 . In the ROM  16 , however, coexistence relationship information is also recorded, in addition to definitions of the display areas and the display control program. 
     FIG. 14  shows the definitions of the display areas in this embodiment. In this embodiment, the display area E 1  for the entire screen, the display area E 2  for the left half, the display area E 3  for the right half, the display area E 4  for the upper half, and the display area E 5  for the lower half are defined. This definition content is stored in the ROM  16  as a display area definition table, as shown in  FIG. 15 . Also, as  FIG. 16  shows, the work memory  14  stores the acquisition status storage table which indicates the correspondence between a display area and the processing unit which acquires this area. In this embodiment, a key number is assigned to a processing unit which is allowed to display, as mentioned later. This key number is also stored in the acquisition status storage table. 
     FIG. 17  shows the coexistence relationship table stored in the ROM  16 . In this embodiment, areas cannot coexist if they overlap. In  FIG. 17 , display areas which cannot coexist are recorded for each display area, but display areas which can coexist may be recorded. 
     FIG. 18  shows a flow chart of the acquisition request processing portion of the display control program recorded in the ROM  16 . Processing when the processing unit R 2  requests acquisition of the display area E 3  while the display area E 2  has been acquired by the processing unit R 1 , as shown in  FIG. 16B , will be explained. In this explanation, the processing unit R 1  is assumed to be the program schedule application and the processing unit R 2  to be the data receiving application. In this case, the program schedule application, which is the processing unit R 1 , is currently executing display in the display area E 2 , as shown in  FIG. 19 . 
   When the acquisition request is received from the task T 21  (for example, a task for displaying the content of data broadcasting on screen), which represents the data receiving application (processing unit R 2 ), the CPU  12  starts the processing shown in  FIG. 18  (Step S 401 ). Then the CPU  12  refers to the acquisition status storage table, and obtains data on which processing unit has acquired each display area (Step S 402 ). In this case, the display area E 2  has been acquired by the program schedule application (processing unit R 1 ) and the other display areas are open. 
   Then referring to the coexistence relationship table in  FIG. 17 , the CPU  12  obtains data on areas which cannot coexist with the display area E 3  requested by the data receiving application (processing unit R 2 ) (Step S 403 ). In this case, the display areas E 1 , E 4  and E 5  are the areas which cannot coexist. 
   Then the CPU  12  judges whether the display area E 3  for which acquisition is requested has been acquired by another processing unit. Also the CPU  12  judges whether one of the display areas E 1 , E 4  and E 5 , which cannot coexist with the requested display area E 3 , has been acquired by another processing unit. If one of these areas E 3 , E 1 , E 4  and E 5  has been acquired by another processing unit, the CPU  12  returns an acquisition failure notice to the task which sent the request (Step S 408 ). 
   In this case, all the display areas E 3 , E 1 , E 4  and E 5  are open, so processing advances to Step S 405 . In Step S 405 , the processing unit R 2  and the key number, corresponding to the display area E 3 , are stored in the acquisition status storage table (see  FIG. 16C ). The CPU  12  sends the key number to the task T 21  representing the data receiving application (processing unit R 2 ) to notify that use of the display area is allowed (Step S 406 ). The task T 21  receives the key number and notifies that the use of the display area E 3  is allowed along with the key number to the other tasks T 22 -T 2   n  (for example, a task for displaying the main menu, and a task for displaying the sub-menu) belonging to the data receiving application (processing unit R 2 ). In this way, use of the display area E 3  is allowed to the data receiving application (processing unit R 2 ). In this embodiment, a key number, including date and time when use is allowed, is generated and assigned. In this case, the key number “3205151307” is generated as area number “3”, processing unit number “2”, month “05”, day “15”, hour “13” and minute “07”. The key number may be generated by another encryption processing. 
   In this embodiment, it is supervised whether the display processing instructions sent from each task belonging to each processing unit is for the display area for which use is allowed.  FIG. 20  shows a flow chart of the supervisory processing program (display processing supervisory means). Supervision of display processing by the task T 22  belonging to the data receiving application (processing unit R 2 ) which obtained the display area E 3  will be explained below. 
   The task T 22  of the data receiving application notifies the requesting display area E 3 , the assigned key number “3205151307” and the display content (for example, “straight line, x1=10, y1=20, x2=10, y2=80”) to the CPU  12 . Receiving this, the CPU  12  starts the processing in  FIG. 20  (step S 501 ). At first, the CPU  12  refers to the acquisition status storage table in Step S 502 , and recognizes that the key number of the display area E 3  is “3205151307” (see  FIG. 16C ). Then the CPU  12  judges whether the key number notified by the task T 22  which requested display processing and the key number of the acquisition status storage table match (Step S 503 ). 
   When they do not match, the CPU  12  does not execute display processing regarding that the task belonging to a processing unit which is not allowed use of the display area attempts invalid display processing. In other words, the display content is not displayed. 
   In this case, the key number “3205151307” matches, therefore the CPU  12  judges the display processing request as valid, and executes the display processing for the display area E 3  (Step S 504 ). As a result, the display content is displayed. This display processing may be executed by the CPU  12 , or by another CPU or circuit. 
   In this way, the program schedule application uses the area E 2  at the left, and the data receiving application uses the area E 3  at the right. If the program schedule application attempts display processing for the area E 3 , or if the data receiving application attempts display processing for the area E 2 , then the display processing is disabled by the supervisory processing program. Thus the program is supervised so as to maintain an appropriate display by disabling display processing by a task belonging to a processing unit which is not allowed use of the display area. 
   Next, the case when the caption application (processing unit R 3 ) requests acquisition of the upper half display area E 4  while the left half display area E 2  has been acquired by the program schedule application (processing unit R 1 ) (see  FIG. 16B ) will be explained. 
   When the acquisition request is received, the CPU starts the processing shown in  FIG. 18  (Step S 401 ). Since another processing unit has acquired the display area E 2 , which cannot coexist with the display area E 4  in Step S 404 , the processing advances to Step S 408 . In Step S 404 , the CPU  12  returns an acquisition failure notice to the processing unit R 3 . In other words, in this embodiment, the left half display area E 2  and the upper half display area E 4  cannot coexist since they partially overlap. 
   In the above case, a key number is not assigned to a task belonging to the processing unit R 3 , therefore display processing for the display area  4  cannot be executed. Even if display processing is attempted, the display processing is disabled by the supervisory processing program shown in FIG.  20 . 
   In this embodiment, a key number is encrypted by including such elements as hour and minute. Therefore even when use of the same display area is allowed, the key number may be different for each assignment. In the case of the status shown in  FIG. 16C , for example, when the processing unit R 1  releases the display area E 2  and the processing unit R 4  is allowed use of the display area, a key number different from the one for processing unit R 1 , that is, “2105151209”, is assigned. As a consequence, even if a task belonging to the processing unit R 1  attempts display processing for the display area E 2  using the old key number, “2105151305”, the display processing is disabled. 
   3.3 Handling of Task Attempted Invalid Processing 
   In the above mentioned case, display processing by a task is not executed if key numbers do not match. However, as Step S 506  in  FIG. 22  shows, subsequent processing may be completely disabled for the processing unit which requested the display processing. In other words, regarding the processing unit as a processing unit which attempted invalid processing, the display area which the processing unit has acquired is forcibly released, resources the processing unit is using are forcibly released, and information on the processing unit recorded in the kernel which is performing task control is deleted, so as to remove the processing unit. In this way, invalid processing by an invalid processing unit can be prevented by removing the processing unit which attempted invalid processing. 
   4. Third Embodiment 
   4.1 Example when Overlapped Areas are not Allowed to Coexist 
   In accordance with the above mentioned first embodiment and second embodiment, when a plurality of processing units request acquisition of display areas which cannot coexist, the processing unit which sent an acquisition request first is allowed use of the display area. However, it is also acceptable that priority be assigned to each display area, and a processing unit which requested a display area which has the highest priority among the plurality of processing units which requested acquisition is allowed use of the display area. 
   An embodiment using this type processing will be explained below. For convenience of explanation, the second embodiment applied to a digital broadcasting receiver is basically used for explanation. 
   In the ROM  16  ( FIG. 3 ), a display area priority table, as shown in  FIG. 23 , has been recorded. The display area priority table defines priority for each display area. In this embodiment, the smaller the number assigned as priority the higher the priority. 
     FIG. 24  shows a flow chart of the acquisition request processing portion of the display control program in accordance with the present embodiment. The following explanation is based on the case when the processing unit R 3  requests acquisition of the display area E 1  (entire area) while the processing unit R 1  has acquired the display area E 2  (left half area), and the processing unit R 2  has acquired the display area E 3  (right half area), as shown in  FIG. 16C . 
   When the acquisition request from the processing unit R 3  is received, the CPU  12  starts the processing shown in  FIG. 24  (Step S 401 ). Then referring to the acquisition status storage table in  FIG. 16C  and the coexistence relationship table in  FIG. 17 , the CPU  12  judges whether the display area E 1  requested by the processing unit R 3  can coexist with the areas which have already been acquired (Steps S 402 , S 403 , S 410 ). Since the display E 1  cannot coexist with the display area E 2  and the display area E 3 , the processing advances to Step S 411 . 
   In Step S 411 , referring to the display area priority table in  FIG. 23 , the CPU  12  judges whether the newly requested display area has a higher priority than the display areas which have been acquired and cannot coexist with the newly requested display area. If the priority is not higher (priority is lower or the same), an acquisition failure notice is sent to the processing unit which requested acquisition (Step S 413 ). Since priority of the display area E 1  requested by the processing unit R 3  is “1”, and priority of the display areas E 2  and E 3  which have been acquired is “2”, the display area E 1  has the higher priority. Therefore processing advances to Step S 412 . 
   In Step S 412 , the display areas E 2  and E 3  which have been acquired are released. In this case, the processing unit R 1  and R 2  are deleted from the display area storage table. Then processing advances to Steps S 405  and S 406 , and the processing unit R 3  is allowed use of the display area E 1 . As a result, use of the screen allowed to processing units R 1  and R 2  is changed to use of the entire screen allowed to the processing unit R 3 . 
   In this way, in accordance with the present embodiment, when acquisition of display areas which cannot coexist is requested, use is allowed to a processing unit which requested a display area having a higher priority. 
   4.2 Example when Overlapped Areas are Allowed to Coexist 
   In the above mentioned case, overlapped areas are not allowed to coexist. However, overlapped areas may be allowed to coexist, where for the overlapped portion, a display area having a higher priority is displayed with priority. 
   In this case,  FIG. 25  shows the definition of the display areas,  FIG. 26  shows a coexistence relationship table, and  FIG. 27  shows a display area priority table. The flow chart of the acquisition request processing is the same as FIG.  24 . 
   Assume that an urgent display application requests acquisition of the top part display area E 4  while an application is using the display area E 1  on the entire screen. In this case, the urgent display application is allowed to use the display area E 4  since the area E 4  can coexist with the area E 1 . 
     FIG. 28  shows a flow chart of the display processing program. It is preferable to provide the display processing program as a part of the operating system (OS). The case when an urgent display application which is allowed to use the display area E 4 , as mentioned above, executes display processing for the display area E 4 , will be explained as an example. At first, the display processing request sent by the urgent display application is judged whether it is a valid request by the supervisory processing shown in  FIG. 22 . If judged as valid because key numbers match, the display processing request is sent to the display processing program of the OS in Step S 504  in  FIG. 22 . 
   When the display processing request is received, CPU judges whether the target area of the display processing request (area E 4  in this case) overlaps with another area for which use has been allowed (Step S 801  in  FIG. 28 ). Since it overlaps with the area E 1  for which use has been allowed here, processing advances to Step S 802 . In Step S 802 , CPU judges whether priority of the target area (E 4  in this case) is higher than that of the other area (E 1  in this case). Since the target area has the higher priority here, processing advances to Step S 803 , and write processing for the target area is executed. In other words, the CPU  12  overwrites the target area (E 4  in this case) portion of V-RAM  42  according to the display processing request. 
   In this way, the urgent display, as shown in  FIG. 29 , is executed. By creating an area for the urgent display to overlap another area and by assigning a higher priority, as shown in this example, an appropriate urgent display becomes possible while efficiently using the screen. 
   When a display request processing is executed for the display area E 1  in the status shown in  FIG. 29 , the processing flow is as follows. Since the other area E 4  has a higher priority in Step S 802 , processing advances to Step S 804 . In Step S 804 , write processing is executed for the target area, excluding the portion of the other area. In other words, the CPU  12  overwrites the target area E 1  portion of V-RAM  42 , excluding E 4 , according to the display processing request. As a result, the display area E 1  can be overwritten without deleting the urgent display of the display area E 4 . 
   5. Fourth Embodiment 
   In accordance with the third embodiment, when a plurality of processing units request acquisition of display areas which cannot coexist, a processing unit which requested a display area having the highest priority is allowed use of the display area. However, priority may be assigned to each processing unit so that a processing unit having the highest priority is allowed use of the display area. 
   In this case, it is preferable that the processing unit priority table shown in  FIG. 30  is stored in the ROM  16 , and the acquisition request processing shown in  FIG. 31  is executed. In  FIG. 31 , when a plurality of processing units request acquisition of display areas which cannot coexist, it is judged whether the processing unit newly requested acquisition has a higher priority than a processing unit which has acquired an area which cannot coexist (Step S 414 ). If the processing unit which newly requested acquisition has a higher priority, the display area of the processing unit which has acquired the display area is released, and the processing unit which newly requested acquisition is allowed use of the display area (Step S 412 ). 
   The order of acquisition requests, priority of the display areas, and priority of the processing units may be freely combined in deciding which processing unit is allowed use of the display area. 
   6. Fifth Embodiment 
     FIG. 32  shows a general configuration of the display control device  2  according to the fifth embodiment of the present invention. In this embodiment, dependency relationship storage means  24  is disposed. In the dependency relationship storage means  24 , display areas which cannot coexist with the requested display area are indicated, and display area change information for making display areas coexist has been recorded. Based on the information of the dependency relationship storage means  24 , the display area management means  4  judges whether a display area which cannot coexist with the requested display area have been acquired by another processing unit. When the display area has already been acquired, the display area management means  4  changes the already acquired display area of the processing unit for making it coexist based on the information of the dependency relationship storage means  24 , and allows the processing unit which requested acquisition use of the requested display area. 
   The hardware configuration, when the display control device  2  in  FIG. 32  is applied to a digital broadcasting receiver, is the same as in  FIG. 3 . In the ROM  16 , however, dependency relationship information is also recorded, in addition to the definitions of display areas and the display control program. 
   The definitions of display areas in this embodiment are the same as  FIG. 14 , and the content of the display area definition table is the same as  FIG. 15 . The acquisition status storage table is the same as  FIG. 16 . 
     FIG. 33  shows the content of the dependency relationship table for recording dependency information. The dependency relationship table is stored in the ROM  16 . The second line of this table, for example, shows that when acquisition is requested for the display area E 2 , and if the display area E 1  has been acquired by another processing unit, coexistence is made possible by changing the area of another processing unit from E 1  to E 3 . 
     FIG. 34  shows a flow chart of an acquisition request processing portion of the display control program recorded in the ROM  16 . The case when the processing unit R 2  requests acquisition of the display area E 2  while the display area E 1  has been acquired by the processing unit R 1  (see  FIG. 35A ) will be explained below. 
   When an acquisition request is received from the processing unit R 2 , the CPU  12  starts the processing shown in  FIG. 34  (Step S 601 ). At first, referring to the acquisition status storage table, the CPU  12  judges whether the requested display area E 2  has been acquired by another processing unit. If it has been acquired, processing advances to Step S 611 , and the CPU  12  returns an acquisition failure notice to the processing unit R 2 . In this case, the display area E 2  is open, as shown in  FIG. 35A , so the processing advances to Step S 604 . 
   In Step S 604 , referring to the dependency relationship table shown in  FIG. 33 , the CPU  12  obtains information on areas which the requested display area E 2  depends on. In this case, the display areas E 1 , E 4  and E 5  are areas which the display area E 2  depends on. 
   Then referring to the acquisition status storage table, the CPU  12  judges whether the display areas E 1 , E 4  and E 5  which the display area E 2  depends on have been acquired by another processing unit (Step S 606 ). If they have not been acquired by another processing unit, the CPU  12  allows the processing unit which requested acquisition to use the display area in Steps S 607  and S 608 , regarding that use of the display area will not cause any problems in terms of display area coexistence. In this case, the display area E 1  (entire screen area) which the display area E 2  depends on has been acquired by the processing unit R 1 . Therefore if use of the display area E 2  (left half screen area) were allowed to the processing unit R 2 , a part of the display area would overlap and appropriate display would not be executed. 
   So in this embodiment, the display area of the processing unit R 1  is changed from E 1  (entire screen area) to E 3  (right half screen area) according to the dependency relationship table in  FIG. 33  (Step S 610 ). After this change, the processing unit R 2  which requested acquisition is allowed use of the display area E 2  (left half screen area). As a consequence, the processing unit R 1  displays on the right half of the screen, and the processing unit R 2  displays on the left half of the screen. 
   In Steps S 607  and S 608 , the CPU  12  releases the display area E 1 , and at the same time notifies changes to the display area T 3 , a new key number, “3105151322”, to the processing unit R 1 , and sends key number “2205151321” to the processing unit R 2  for the display area T 2 .  FIG. 35B  shows the content of the acquisition status storage table after change. 
   In this way, when acquisition is requested for a display area which cannot coexist, allocation of display areas is changed so that coexistence becomes possible. 
   In accordance with this embodiment, the display area which has been acquired is changed to make coexistence possible, but the display area which acquisition is requested may be changed to make coexistence possible. When the display area E 2  (left half screen area) has been acquired by the processing unit R 1 , for example, if the display area E 1  (entire screen area) is requested by the processing unit R 2 , the request of the processing unit R 2  may be changed to the display area E 3  (right half screen area) for which use is allowed. 
   7. Sixth Embodiment 
     FIG. 36  shows a general configuration of the display control device according to the sixth embodiment of the present invention. In this embodiment, an available resource storage means  28  and a use resource storage means  26  are disposed. The available resource storage means  28  stores information on resources of each processing unit R 1 -Rn. Here the concept “resource” includes not only such hardware as a modem, speaker, video equipment, CD-ROM and DVD drive, but also such software as data and programs. The use resource storage means  26  stores the current availability status of each resource. 
   When a display area acquisition request is received from processing units R 1 -Rn, the display area management means  4  judges whether the display area can coexist with the display areas which have been acquired by other processing units. If coexistence is not possible, the processing unit is not allowed use of the display area. If coexistence is possible, the display area management means  4  obtains information on a resource to be used by the processing unit which requested acquisition referring to the available resource storage means  28 . Then referring to the use resource storage means  26 , the display area management means  4  checks whether the resource can be used now. If the resource cannot be used, the display area management means  4  does not allow the processing unit which requested acquisition use of the display area. This is because allowing use of the display area is meaningless since the processing unit cannot execute processing using the resource. For example, when the processing unit cannot display unless the resource is available, display is not executed even if use of the display area is allowed to the processing unit. 
   With the foregoing in view, it is preferable to judge whether resources required for display processing can be used. A resource which is not directly related to display processing but is very closely related to screen display, such as a speaker, may also be judged whether it can actually be used. In other words, not only resources which the processing unit needs for display processing but also resources required for sound processing related to the display processing may be judged whether they can actually be used. 
   The hardware configuration, when the display control device  2  in  FIG. 36  is applied to a digital broadcasting receiver, is the same as  FIG. 3 . In the ROM  16 , however, the available resource table shown in  FIG. 37  is stored. In the work memory  14 , the use resource table shown in  FIG. 38  is stored. 
     FIG. 39  shows a flow chart of the acquisition request processing portion of the display control program recorded in the ROM  16 . Here, the case when the task T 2  of the processing unit R 2  requests acquisition of the display area E 3  at the lower part of the screen while the task T 1  of the processing unit R 1  has acquired the display area E 2  at the upper right of the screen, as shown in  FIG. 7B , will be explained. It is assumed that the processing unit  2  is a browser application. The browser application accesses the Internet via a modem  17  to read home pages. It is also assumed that the processing unit R 1  is a telephone shopping application which executes display, as shown in  FIG. 40 . Here, the viewer has selected a purchase application, therefore the CPU  12  calls the reception center of the telephone shopping company via the modem  17 . In other words, the modem  17  has already been used by the telephone shopping application (processing unit R 1 ) as shown in  FIG. 38 . 
   When an acquisition request is received from the browser application (processing unit R 2 ), the CPU  12  starts the processing shown in  FIG. 39  (Step S 701 ). Then referring to the acquisition status storage table in  FIG. 7B , the CPU  12  judges whether the requested display area E 3  has been acquired by another processing unit (Steps S 702 , S 703 ). In this case, the display area E 3  is open, so processing advances to Step S 704 . 
   In Step S 704 , referring to the available resource table in  FIG. 37 , the CPU  12  extracts resources to be used by the processing unit R 2  which requested acquisition. In this case, a modem and a speaker are extracted. Then referring to the use resource table in  FIG. 38 , the CPU  12  judges whether the extracted modem and speaker are in use by another processing unit (Steps S 705 , S 706 ). When all extracted resources can be used, the CPU  12  allows use of the display area to the processing unit, and writes that the resources to be used by the processing unit are in use in the use resource table in  FIG. 38  (Steps S 708 , S 709 ). 
   In this case, the modem is in use by the telephone shopping application (processing unit R 1 ), as shown in  FIG. 38 , so processing advances from Step S 706  to S 710 . In Step S 710 , the CPU  12  notifies the browser application (processing unit R 2 ) that display area acquisition failed. In this way, it is judged whether use of the display area is allowed considering the use status of resources. 
   When a processing unit requests to release an area, the CPU  12  writes the release of the resource which the processing unit has been using in the use resource table. As a consequence, always the latest use status is stored in the use resource table. 
   In accordance with the above embodiment, the resource cannot be used if another processing unit is using it. However, for a resource which specified the number of processing units (or tasks) that can be used simultaneously, whether that resource can be used may be judged by the number of processing units (tasks) which are actually using the resource. 
   In the above explanation, use of the display area is allowed after judging whether such a resource as a modem is available. However, when the processing unit is for displaying the data of an electronic program schedule, use of the display area may be allowed after judging whether the data is actually received. In other words, the resources include not only hardware but also such software as data. 
   8. Seventh Embodiment 
   In accordance with the above embodiments, when acquisition is requested for a display area which cannot coexist, an acquisition failure notice is returned to the processing unit. However, the processing unit which is not allowed use of the display area may be stored as acquisition waiting, so as to acquire the display area when use can be allowed. 
   This embodiment will be explained based on the second embodiment in  FIG. 13 . The flow chart of acquisition request processing is shown in  FIG. 41 , instead of  FIG. 18 . The flow chart of release request processing is shown in  FIG. 42 . In the work memory  14 , the acquisition waiting table, as shown in  FIG. 43 , is stored. 
   Here, the case when the content of the acquisition status storage table is in the status shown in  FIG. 16C  (that is, the status when the processing unit R 1  is using the left of the screen and the processing unit R 2  is using the right of the screen) and the processing unit R 4  newly requests acquisition of the display area E 2  will be explained. It is assumed that nothing has been stored in the acquisition wait table, as shown in  FIG. 43A . 
   When an acquisition request from the processing unit R 4  is received, the CPU  12  refers to the acquisition status storage table ( FIG. 16 ) and coexistence relationship table ( FIG. 17 ), and judges whether use of the display area E 2  can be allowed (Step S 402 , S 403 , S 404 ). In this case, the display area E 2  has been acquired by the processing unit R 1  and cannot coexist, so processing advances to Step S 410 . 
   In Step S 410 , the CPU  12  notifies acquisition waiting to the processing unit R 4 , and the CPU  12  stores information that the processing unit R 4  is waiting for acquisition of the display area E 2  in the acquisition wait table (Step S 411 ). 
   When processing units have already been stored in the acquisition wait table, the processing units may be rearranged according to predetermined priority. In other words, the processing units are rearranged such that a processing unit with a higher priority comes first. For the priority used for this rearrangement, the order of sending acquisition requests, priority assigned to the requested display areas (see  FIG. 23 ), and priority assigned to processing units ( FIG. 30 ), for example, can be used. 
   In this way, the processing unit which is not allowed use is stored in the acquisition wait table. 
   Next, release request processing will be explained referring to  FIG. 42 . Here, it is assumed that the processing unit R 1  requests the display area E 2  in the status shown in  FIG. 16C  for explanation. The acquisition wait table is assumed to be in the status shown in  FIG. 43B . 
   When the release request is received, the CPU  12  refers to the acquisition status storage table, and judges whether the processing unit R 1  which requested release of the display area E 2  has acquired the display area E 2  (Steps S 302 , S 303 ). Since the processing unit R 1  has acquired the display area E 2  in this case, the CPU  12  deletes the processing unit R 1  from the acquisition status storage table and returns a release OK notice (Steps S 304 , S 305 ). 
   Then the CPU  12  advances to Step S 310  and reads the acquisition wait table, shown in  FIG. 43B , from the beginning. Here, the request by the processing unit R 4  for the display area E 2  is read. For this acquisition request in wait status, the CPU  12  executes processing of the acquisition request in wait status, as shown in  FIG. 44 . Since the area E 2  requested by the processing unit R 4  can coexist in this case, processing advances from Step S 404  to S 405 . 
   In Step S 405 , the CPU  12  stores the processing unit R 4  in the acquisition status storage table and returns the key number to the processing unit R 4  (Steps S 405 , S 406 ). Then the CPU  12  deletes the acquisition request by the processing unit R 4  for the display area E 2  from the acquisition wait table (Step S 412 ). 
   In this way, the processing unit R 4  can be allowed to acquire the display area at the point when use of the display area becomes possible. 
   Then the CPU  12  reads the next acquisition request stored in the acquisition wait table, and executes the processing shown in  FIG. 44  for this request as well. This is because two or more requests may be allowed to use a respective area when the released area is large. After executing processing for all acquisition requests in wait status in the order of priority, the CPU  12  ends release request processing (Step S 407 ). 
   In accordance with this embodiment, each processing unit which requested acquisition is eventually allowed use of the respective area according to the change of status even if use is not immediately allowed. 
   9. Other Embodiments 
   In the above embodiments, the case when the present invention is applied to a digital broadcasting receiver was explained, but the present invention can be applied to equipment where a plurality of applications execute display processing. In other words, the present invention can be applied to equipment having the basic configuration shown in  FIG. 12  (the work memory  14  and the ROM  16  may be integrated). For example, the present invention can be applied to a home game machine, a telephone with display and a personal computer. 
   In a car navigation system, the present invention can be applied for displaying map information and Internet information, for example. 
   Also in a DVD system, the present invention can be applied when image information and such text information as a menu are displayed during the authoring of images. 
   The present invention can also be applied to the screen display of a personal computer. Particularly, the present invention is effective for computers used in factory automation (FA), where the user cannot change the screen display format. 
   In the above embodiments, the tasks T 1 -Tn for carrying out display processing are executed by the CPU  12 , but may be executed by another CPU. 
   Also in the above embodiments, display areas have been defined in advance, but the user may change the size and position of the display areas. 
   Also in the above embodiments, each means in the general configuration is implemented by the CPU, but a part or all of the means may be configured by hardware logic. 
   10. Eighth Embodiment 
   10.1 General Configuration 
   In accordance with the above embodiments, it is judged whether the display area subject to the acquisition requested can coexist with other display areas which have been used, and if coexistence is possible, use of the display area is allowed. However, processing units which are allowed use of the display area may be predetermined for each display area so that allowing use of the display area is judged according to this information. 
     FIG. 45  shows the general configuration of the display control device  2  according to the eighth embodiment. The display area storage means  6  stores definitions of the display areas set on the screen of the display device  8 . In this embodiment, acquisition right information storage means  30  connected to the display area management means is disposed. The acquisition right information storage means  30  stores processing units which can be allowed use of the display area for each display area. When one of the tasks T 1 -Tn requests acquisition of a display area, the display area management means  4  judges whether use of the display area can be allowed to the task based on the content stored in the acquisition right information storage means  30 . If the acquisition right for the requested display area is given to the task in the acquisition right information storage means  30 , use is allowed. If the acquisition right is not given, use is not allowed. 
   10.2.1 Example when One Processing Unit is Allocated to One Display Area 
   The hardware configuration, when this embodiment is applied to digital satellite broadcasting, is shown in  FIG. 3 .  FIG. 46  shows a display area definition example in accordance with this embodiment.  FIG. 47  shows the display area definition table stored in the ROM  16 . And  FIG. 48  shows the acquisition right information table stored in the ROM  16 . According to this acquisition right information table, use of the display area E 1  is allowed to the task T 1 , use of the display area E 2  is allowed to the task T 2 , and use of the display area E 3  is allowed to the task T 3 . 
     FIG. 49  shows a flow chart of the acquisition request processing portion of the display control program stored in the ROM  16 . For example, the case when the task T 3  requests acquisition of the display area E 1  will be explained. At first, the CPU  12  obtains the acquisition right information table from the ROM  16  (Step S 901 ). Then the CPU  12  judges whether the task T 3 , which requested the acquisition, has an acquisition right for the display area E 1  referring to the acquisition right information table (Step S 902 ). In this case, the task T 3  does not have an acquisition right for the display area E 1 , so the CPU  12  notifies an acquisition failure to the task T 3  (Step S 904 ). 
   When the task T 1  requests acquisition of the display area E 1 , the CPU  12  also judges whether use is allowed referring to the acquisition right information table in the same manner (Step S 902 ). In this case, the task T 1  has an acquisition right for the display area E 1 , so the CPU  12  notifies an acquisition OK to the task T 1  (Step S 903 ). 
   In this way, in accordance with this embodiment, each display area is defined so as not to overlap, and only one processing unit (task) is allowed use of each display area, therefore the display of each task does not overlap and is not lost. 
   10.3 Example when a Plurality of Processing Units are Allocated to One Display Area 
   The acquisition right information table may be defined as shown in  FIG. 50 , so that one display area can be used by a plurality of tasks (processing units). In this state, acquisition request processing is executed so that only one task (processing unit) is allowed use of each display area. For example, when the task T 1  requests acquisition of the display area E 1 , use is allowed if no other tasks have acquired the display area. When the task  1  requests acquisition of the display area E 1 , use is not allowed when another task (task T 2  or T 5 ) has acquired the display area. 
   In this way, when a plurality of tasks (tasks which have an acquisition right for the display area) request acquisition of one display area, the task which requested acquisition first is allowed use of the display area. However, the task which requested acquisition last may be allowed use of the display area. Also priority may be assigned to each task in advance so that a task which has the highest priority is allowed use of the display area. 
   10.4.1 Example when a Plurality of Tasks are Allowed to Use One Display Area 
   In this example, when a plurality of tasks (tasks which have an acquisition right for the display area) request acquisition of one display area, a plurality of tasks which requested acquisition are allowed use of the display area. In this case, display processing is executed by the plurality of tasks which are allowed use of the display area for the one display area. Therefore, in this case, display processing among the plurality of tasks which are allowed use of the one display area is adjusted among the tasks. In other words, an adjustment of display processing among the tasks is necessary, but this adjustment among the tasks is easy since the number of tasks which can use each display area is limited. 
   The upper limit of the number of tasks (number of processing units) which can be used simultaneously may be defined in the acquisition right information table, as shown in  FIG. 51 . In this table, use of the display area E 1  is allowed to the tasks T 1 , T 2  and T 5 , but the number of tasks which can be allowed simultaneously is defined as 2. Use of the display area E 2  is allowed to the task T 2 , and the number of tasks which can be allowed simultaneously is defined as 1. Also, use of the display area E 3  is allowed to the task T 3  and T 4 , and the number of tasks which can be allowed simultaneously is defined as 2. In this embodiment, the work memory  14  has the acquisition status storage table shown in  FIG. 53 , to manage the number of tasks using each display area. 
     FIG. 52  shows a flow chart of acquisition request processing in accordance with this embodiment. Here, the case when the task T 5  requests acquisition of the display area E 1  while the tasks T 1  and T 2  have been allowed use of the display area E 1 , as shown in  FIG. 53 , will be explained as an example. 
   At first, the CPU  12  obtains the acquisition right information (Step S 1001 ), and judges whether the task T 5  has an acquisition right for the display area E 1  (Step S 1002 ). In this case, the task T 5  has the acquisition right (see  FIG. 51 ), so processing advances to Step S 1003 . In Step S 1003 , the CPU  12  obtains information on the number of tasks using the display area E 1  referring to the acquisition status storage table in  FIG. 53 . In this case, the CPU  12  recognizes that two tasks, T 1  and T 2 , are using the display area E 1 . 
   Then the CPU  12  judges whether the number of tasks using the display area, which is 2, is smaller than the number of tasks which can use the display area written in the acquisition right information table, which is 2 (Step S 1004 ). In this case, the former is not smaller than (equal to) the latter, so the CPU  12  judges that no more tasks are allowed use of the display area, and notifies an acquisition failure (Step S 1007 ). 
   In this way, tasks exceeding the number of tasks which can use the display area are not allowed use of the display area. By limiting the number of tasks which can use the display area like this, the adjustment of display processing among tasks is prevented from becoming complicated. 
   In the above embodiment, the CPU  12  refers to the acquisition right information table, as shown in  FIG. 50 , and the task T 3  is not allowed use of the display area E 1 , for example. However, a task which is not written in the acquisition right information table, such as the task T 3 , may be allowed use of the display area if acquisition is requested by the task alone, so that when acquisition is requested by a task having an acquisition right (e.g. T 1 ), the task having the acquisition right is allowed use of the display area and use by the task T 3  is cancelled. 
   The eighth embodiment can be implemented by combining with one of the first to seventh embodiments. Also for the eighth embodiment, a modification similar to the second to seventh embodiments can be applied to the first embodiment. 
   While the embodiments of the present invention, as disclosed herein, constitute preferred forms, it is to be understood that each term was used as illustrative and not restrictive, and can be changed within the scope of the claims without departing from the scope and spirit of the invention.