Abstract:
A digital television transmitter transmits a transport stream (hereinafter referred to as “TS”) comprising content data for a plurality of channels to receivers. In the transmitter, program information is periodically inserted in the TS; and an expected time of program alteration is included in said TS. A television receiver comprises a first portion always supplied with an electric power, a second portion which, if supplied with a second electric power, becomes capable of collecting program information included in said TS in corporation with said first portion, and a third portion which. if supplied with a third electric power, becomes capable of displaying said program. At an expected time of program alteration previously received, the second power is supplied to the second portion to collect program information, which is preferably stored in nonvolatile memory. The transmitter sending an alert signal to the receiver via a second transmission media ensures the reception of changed or special program information.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention generally relates to a digital video channel broadcasting system comprising a transmitter and a multiplicity of receivers and, more particularly, to a method and subsystem for use in such a system for effectively transmitting and receiving program information while reducing the electric power consumed for program information reception in each receiver. 
     2. Description of the Prior Art 
     In a digital television broadcasting system such as a satellite broadcasting, a CATV (cable television) system, etc., a broadcasting station or transmitter periodically transmits program information by including the program information in a transport stream, which comprises time-division multiplexed program data for a plurality of channels. The program information is received and stored by television receivers for displaying a program guide in response to a user&#39;s request. However, a program may be changed and a special or emergency broadcast may be delivered at any time. For this reason, in order to cope with the changes in program and special or emergency broadcasts, television (TV) receivers have to keep on receiving the program information even when no channel is viewed, causing the electric power consumption of each TV receiver to be increased. 
     Japanese unexamined patent publication Hei.9-275,530 discloses “TELEVISION RECEIVER” as a solution to this problem. In the TV receiver, a controller is always supplied with electric power. A first power supply to a tuner and a signal processing circuit and a second power supply to an audio circuit, a driver circuit, a display device and a loudspeaker are controlled by the controller. The electronic program guide (EPG) is received only at times preset by the user, in which only the first power supply is effected. Both the first and second power supplies are effected during the user viewing a program, and none of them is effected otherwise. 
     However, if any change in the EPG has been made after the last time of EPG reception, the change will not be reflected in a TV program schedule displayed by a command from the user. Further, any special or emergency broadcast which is not included in the last EPG data is missed in the above-cited prior art. 
     It is an object of the invention to provide a digital TV transmitter and a receiver that ensures the reception of program information and any irregular program while saving the power consumption in the receiver. 
     Generally speaking, only a part of EPG data has been changed even in EPG data received at a relatively long interval such as several hours. Therefore, it is not efficient to update all of the stored program information each time of EPG data reception. 
     It is another object of the invention to provide a digital TV transmitter and a receiver that saves the power consumption in the receiver by updating only data portions of the stored program information which include changed EPG data. 
     If a receiver has a memory with a capacity insufficient to store all of the received EPG data, it will take some time to collect EPG data which has not stored in the memory and to display program information in response to a program schedule display command from the user. 
     It is still another object of the invention to provide a digital TV transmitter and a receiver that first displays programs of higher priorities which have been stored in nonvolatile memory and then displays programs of lower priorities which have been received after the detection of a program information display command for providing a quick response. 
     SUMMARY OF THE INVENTION 
     A digital television transmitter transmits a transport stream (hereinafter referred to as “TS”) comprising content data for a plurality of channels to receivers. In the transmitter, program information is periodically inserted in the TS; and an expected time of program alteration is included in said TS. A television receiver comprises a first portion always supplied with an electric power, a second portion which, if supplied with a second electric power, becomes capable of collecting program information included in said TS in corporation with said first portion, and a third portion which, if supplied with a third electric power, becomes capable of displaying said program. At an expected time of program alteration previously received, the second power is supplied to the second portion to collect program information, which is preferably stored in nonvolatile memory. 
     Since the transmitter can send an alert signal to the receiver via a second transmission media, it is ensured that the receivers can receive changed program information and program information for special or emergency broadcast. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The features and advantages of the present invention will be apparent from the following description of an exemplary embodiment of the invention and the accompanying drawing, in which: 
     FIG. 1 is a diagram showing an exemplary arrangement of a digital TV broadcasting system in accordance with an illustrative embodiment of the invention; 
     FIG. 2 is a schematic diagram showing an arrangement of the above mentioned program information record; 
     FIG. 3 is an example of an expected alteration time list at 15:00 of 12/10; 
     FIG. 4 is a flow chart showing an exemplary operation executed by the computer  202  when a new program information record  300  has been added to the database or any program information record  300  of the database has been altered; 
     FIG. 5 shows an exemplary emergency code format; 
     FIG. 6 is a diagram showing an example of an update time list at 16:00 of 12/17; 
     FIGS. 7A and 7B, when combined at encircled letters A and B, constitute a flow chart showing an exemplary operation of the controller  225  collecting the program information in response to the reach of a first time and date in the update time list of FIG. 6 in accordance with the illustrative embodiment of the invention; 
     FIG. 8 is a diagram showing an exemplary structure of a program guide table that contains program information for each program of each channel; 
     FIG. 9 is a flow chart showing an exemplary operation of an interrupt subroutine executed by the controller  225  in response to an interrupt from the communication IF  228 ; 
     FIG. 10 is a flow chart showing an exemplary operation executed before the operation of FIG. 7; 
     FIG. 11 is an exemplary step to be inserted between the steps  454  and  460  of the flow chart of FIG. 7; 
     FIG. 12 is a flow chart showing an exemplary operation executed in stead of step  456  to save the capacity of the nonvolatile memory  226 ; 
     FIG. 13 is a diagram showing an example of a priority table; 
     FIG. 14 is a diagram showing an exemplary readiness map defined when the user issued a program time table display command at a time from 3 p.m. and to 4 p.m. of December 17; 
     FIG. 15 is a flow chart showing an exemplary operation of displaying a program time table in accordance with the principles of the invention; and 
     FIG. 16 is a diagram showing an exemplary readiness map defined when the display area is set for the channels  7  through  14  and for hours from 12/17 19:00 to 12/18 7:59. 
     Throughout the drawing, the same elements when shown in more than one figure are designated by the same reference numerals. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a diagram showing an exemplary arrangement of a digital TV broadcasting system in accordance with an illustrative embodiment of the invention. The present invention is applicable to any broadcasting system that frequently transmits program information together with the program contents in a multiplexed manner. However, in FIG. 1, the digital TV broadcasting system  1  is assumed to be a satellite broadcasting system. The broadcasting system  1  comprises at least one broadcasting satellite earth station or digital TV transmitter  2  for transmitting a transport stream comprising a plurality (M) of channels, a broadcasting satellite space station  3  which relays transport streams including the one from the digital TV transmitter  2 , a multiplicity of digital TV receivers  4  for receiving the transport streams from the space station  3 , and a second transmission media  5  which enables the digital TV transmitter  2  to inform the TV receivers  4  of irregular broadcasts such as special and emergency broadcasts and/or changes in the program information. The second transmission media  5  may be any transmission media which is other than the broadcasting satellite  3  and which causes the power consumption in each TV receiver  4  during waiting for a communication from the earth station  2  to be less than the power consumption in each TV receiver  4  during receiving the program information without using program contents, i.e., without displaying any program. Some examples of the second transmission media  5  are a telephone network, a power line, an AM (amplitude modulation) or FM (frequency modulation) radio wave, a CATV, etc. 
     The digital TV transmitter  2  comprises M channel units  201  each for supplying a contents data stream of each of the programs for the channel; a computer  202  for preparing and storing PSI (Program Specific Information described later) data and SI/EPG (Service Information/Electronic Program Guide) data; a data buffer  203  for temporarily storing the PSI and SI/EPG data (or program data or information); a transmission unit  204  for multiplexing and transmitting the contents data streams and the program information; and a transmission controller  205  for controlling the data buffer  203  and the transmission unit  204 . In order to communicate to the subscriber TV receiver  4 , the digital TV transmitter  2  further comprises a communication interface  206  for providing the computer  202  with an interface to the second transmission media  5 . The received signal processor  211  comprises a tuner  213  for selecting a specified one of the received transport streams; a VIF/SIF (video intermediate frequency processor and sound intermediate frequency processor) for extracting the PSI and SI/EPG data, and a video signal and an audio signal for a channel specified by a control signal from the controller  225  from the selected transport stream; and a video signal processor (labeled “V”)  215 . The output portion  212  comprises deflecting circuits (labeled “V OUT”)  216 ; an audio signal processor and output circuit (A PRO/OUI)  217 ; and video and audio output devices  218 . 
     If the second transmission media  5  is a public-switched telephone network then the second transmission media  5  preferably comprises first relay points (not shown), placed in respective areas in a nation or a service area of the digital TV, for relaying the communication from the digital TV transmitter  2 ; second relay points (not shown), placed in respective smaller areas in each area, for relaying the communication from an associated first relay point; and terminal relay points (not shown) placed in exchange offices in each smaller area for relaying the communication from an associated second relay point to the subscriber TV receivers  4  serviced by respective exchange offices. 
     The digital TV receiver  4  comprises a received signal processor  211  for processing received signals to provide a video signal and an audio signal for a specified channel in a transport stream which contains the specified channel and to provide EPG data; an output portion  212  for providing a video and audio output in response to the video signal and the audio signal; a controller  225  for controlling the received signal processor  211 , a nonvolatile memory  226  for storing the program information, I/O devices  227  which enable the user to control the digital TV receiver  4 ; and at least one electric power supply  230 . In order to be informed by the TV transmitter  2 , the digital TV receiver  4  further comprises a communication interface  228  for providing the controller  225  with an interface from the second transmission media  5 . 
     A first electric power is always supplied from a first power terminal  230   a  of the power supply  230  through conductors shown in solid lines to the controller  225 , the I/O devices  227  and the communication interface (IF)  228  so that the TV receiver  4  can be informed at any time by the TV transmitter  2 . The TV receiver  4  further comprises a switch circuit  231  inserted between the first power terminal  230   a  and a conductor leading to the received signal processor  211  and the nonvolatile memory  226  and a switch circuit  232  inserted between a second power terminal  230   b  of the power supply  230  and the output portion  212 . The control terminals of the switch circuits  231  and  232  are connected with respective control output terminals of the controller  225 . This enables the controller  225  to control independently respective supplies of a second electric power from the switch circuit  231  and a third electric power from the switch circuit  232 . When neither a channel nor the program information is received, both the switches  231  and  232  are controlled to open. When only the program information is being received without receiving any channel, the switch  231  is kept closed while keeping the switch  232  open. When any channel is being viewed, both the switches  231  and  232  are kept closed. 
     In operation, the operator of the TV transmitter  2  creates a program information database (not shown) for storing program information in the computer  202  and enters a program information record for each of the programs within at least a predetermined period, e.g., 48 hours for each of the channels  1  through M. 
     FIG. 2 is a schematic diagram showing an arrangement of the above mentioned program information record. In FIG. 2, the program information record  300  comprises channel ID field  310 , program guide data fields  320 , and PSI data fields  305 . This program information record  300  is created for each broadcasting program of each channel. The channel ID field  310  contains an ID of the channel i (1≦i≦M). The program guide data fields  320  contain a program ID  321 , a program name  322 , the category  323  of the program, start time and date  324 , end time and date  325 , a channel ID  326 , create/change time &amp; date  327 , time to be changed  328 , a priority  329  and other descriptive data  330 . The create/change time &amp; date  327  is a time when the program information record  300  has been created or altered last. The value of the create/change time &amp; date  327  is automatically set in the create/change time &amp; date field  327  by the computer  202  when the program information record  300  is added or altered. The operator is permitted to include the priority  329  data and/or the time to change  328  in the program information record  300  if necessary. The priority  329  is set by the operator for the program information record  300 . 
     The use of Expected Program Alteration Time 
     The time to change  328  is the expected time of alterations to the program information record  300 . This information is used for programs some details of which can not be decided till a certain event occurs. An example of such programs is a relay broadcast of a game or match in which one of the competitors can not be decided till a particular game or match is over. This information enables the TV receivers  4  to update the program information stored in the nonvolatile memory  226  at the time to change  328 . In other words, the value of the time-to-change field  328  triggers an operation of the TV receiver  4  collecting program information at the time specified by the time-to-change field  328 . It is noted that the alteration to the program information record  300  has to be completed sufficiently, say, some minutes before the expected time of the alteration so that the transmission of altered program information record  300  is started before the time to change  328 . In a preferred embodiment, the time to change  328  is so adjusted that the time interval between any adjacent times to change  328  is not shorter than a predetermined time period, say, one hour. In order to facilitate the operation, the computer  202  preferably keeps an expected alteration time list  340  as shown in FIG.  3 . In this example, alterations are scheduled at 15:30, 18:00 of 12/17 and 11:30 of 12/18. 
     The program information records  300  in the program information database are frequently compiled into SI/EPG packets, which is multiplexed with the channel data streams more frequently, e.g., every one through several seconds for transmission. 
     FIG. 4 is a flow chart showing an exemplary operation executed by the computer  202  when a new program information record  300  has been added to the database or any program information record  300  of the database has been altered. In step  402 , the current time is stored in the create/change time field  327  of the program information record  300 . In step  404 , a test is made to see if the record  300  is an added one. If so, a test is made in step  406  to see if a value exists in the time-to-change field  328  of the record  300 . If the test result is NO in step  404  or  406 , then the control is passed to step  418 , where the past value(s) or the value(s) indicative of a time before the current time is (or are) deleted from the expected alteration time list  340  of FIG.  3 . Then in step  420 , the record  300  is compiled into PSI data and the PSI data is passed to the data buffer  30 , terminating the operation. 
     If the test result is YES in decision step  406 , a test is made in step  408  to see if the list  340  contains a value within a preset period or interval (say, one hour) after the time to change  328  in the record  300 . If so, the value is stored in the time-to-change field  328  of the record  300  in step  410  and the control is passed to step  418 . Thereafter, the steps  418  and  420  are executed as described above. 
     If the test result is NO in step  408 , then another test is made in step  412  to see if the list  340  contains a value within the preset period or interval before the time to change  328  of the record  300 . If so, the value plus the preset period is stored in the time-to-change field  328  of the record  300  in step  414 . If a longer interval is permitted between program information collections, the preset period may be added to the value of the time-to-change field  328  in step  414 . 
     After step  414  or if the test result is NO in step  412 , the control is passed to step  416 , where the value of the time-to-change field  328  is added to the expected alteration time list  340 . Thereafter, the steps  418  and  420  are executed as described above and then the operation is terminated. 
     By doing this, the TV transmitter  2  can inform the TV receivers  4  of the expected alteration times for the programs the expected alteration time of which can be determined in advance. 
     In addition to the above operation, program information update (or collection) times that are set periodically or at the operator&#39;s discretion may be transmitted. This enables the TV receivers  4  to update the program information for programs whose program information has been changed unexpectedly. Preferably, the program information update (or collection) times are also listed in order of time in the expected alteration time list  340 . 
     It is also noted that the TV transmitter  2  may transmit a predetermined emergency code indicative of an emergency or special broadcast. Assuming that the emergency code is represented as C em , the emergency code has the following format as shown in FIG.  5 . 
     
       
         C em [time and date], 
       
     
     where [time and date] is option. Specifically, if the emergency code is transmitted alone without time and date, this means that an emergency broadcast is being delivered. If the emergency code is accompanied by time and date, this means that an emergency broadcast is going to be delivered at the time and date. 
     However, the TV receivers  4  that are informed of the on-going or expected emergency broadcast are only TV receivers that happens to be executing a program information collection operation or to be receiving any channel during the transmission of the emergency codes. The other TV receivers  4  can not know the emergency broadcast. In order to ensure the reception of any emergency broadcast, the TV receivers  4  are preferably alerted through the second transmission media  5 . 
     Alerting Through the Second Transmission Media  5   
     If an irregular broadcast such as an emergency broadcast is scheduled in advance, the operator may enter a program information record  300  for the irregular broadcast, including the emergency code with a broadcasting time and date. In response to the detection of the emergency code, the computer  202  places alert calls to predetermined relay points if the second transmission media is a PSTN (public switched telephone network). In this case, the computer  202  may place the alert call either immediately after the detection of the emergency code or at the time accompanying the emergency code. 
     If there is no time to inform of an emergency broadcast in advance, the operator immediately puts an emergency broadcast while transmitting a special program information record including the emergency code with no time and date accompanied. In response to the detection of the emergency code, the computer  202  again places alert calls to predetermined relay points. Doing this ensures the reception of an emergency broadcast. 
     On the other hand, the digital TV receiver  4  updates the program information stored in the nonvolatile memory  226  by collecting EPG data during viewing a channel and in program information collection operations. The program information collection operations are triggered by the above-described times to change (or expected alteration time)  328  extracted in the program information record  300  and the program information update (or collection) times. For this purpose, each TV receiver  4  preferably keeps an update time list that is the same as the expected alteration time list  340 . FIG. 6 is an example of an update time list at 16:00 of 12/17. The update time list  340   a  contains expected alteration times  328  as well as program information update times in order of time. It is seen from FIG. 6 that the TV receiver  4  has received 12/17 21:00, 12/18 18:00 and 12/18 21:00 either as expected alteration times or program information update times in the program information collection operation at the expected time of 12/17 15:30. 
     FIGS. 7A and 7B, when combined at encircled letters A and B, constitute a flow chart showing an exemplary operation of the controller  225  collecting the program information in response to the reach of a first time and date in the update time list of FIG. 6 in accordance with the illustrative embodiment of the invention. In step  444 , the controller  225  turns on the switch  231  to receive a transport stream. In step  446 , a test is made to see if the emergency code is detected. If so, a test is made in step  448  to see if the emergency code C em  is accompanied by a time and date. If not, meaning that an emergency broadcast is on the air, then the controller  225  further turns on the switch  232  selecting the channel delivering the emergency broadcast in step  450  and ends the operation. It is noted that instead of turning on the switch  232 , the controller  225  may alert the user by lighting an indicator or making a sound in step  450 . 
     If the emergency code C em  is accompanied by a time and date in step  448 , the controller  225  saves the time and date and the channel on which the emergency broadcast is delivered in a predetermined memory location in step  452 . 
     After step  452  or if the test result is NO in step  446 , the control is passed to step  454 , where a test is made to see if the received program guide record is new one. 
     It is noted that the controller  225  maintains a program information table as shown in FIG.  8 . Each ( 300   a ) of the records of the program guide table of FIG. 8 is almost similar to the program information record  300 . Each program guide record  300   a  comprises a channel ID  326 , a program ID  321 , a program name  322 , the category  323  of the program, start time and date  324 , end time and date  325 , create/change time &amp; date  327 , time to be changed  328 , a priority  329  and other descriptive data  330   a.    
     If the received program guide record is not found in the program guide table of FIG. 8, i.e., if YES in step  454 , then the program guide record is added to the table of FIG. 8 in step  456  and, if the time-to-change field  328  has a value, the value of the time-to-change field  328  is added to the update time list  340   a  in step  458 . 
     If the test result is NO in step  454 , a test is made in step  460  to see if the received program guide record  300   a  has been altered, i.e., if the create/change time and date of the received record differs from the corresponding field of the corresponding record of the program guide table of FIG.  8 . If so, the controller  225  updates the program guide table record with the received program guide record in step  462 . In this way, updating only the program guide records which have been altered contributes to the reduction in operation time for the program information collection and accordingly to the reduction in the power consumption. 
     In step  464 , the controller  225  makes a test to see if the time-to-change field  328  of the program guide table of FIG. 8 has been changed. If so, then the controller  225  deletes the corresponding value from the update time list  340   a  and adds the value of the time-to-change field  328  to the update time list  340   a  in step  468 . 
     After step  458  or  468 , or if the test result is NO in step  460  or  464 , the controller  225  proceeds to step  470 , where a test is made to see if the time and date saved in step  452  is reached. If so, the controller  225  turns on the switch  232  selecting the channel which is expected to deliver an emergency broadcast in step  472 . Otherwise, the controller  225  makes another test in step  474  to see if all kinds of SI/EPG packets have been exhausted. If so, the controller  225  ends the operation, and otherwise returns to step  446 . 
     The above-described operation is executed at each of the times listed in the update time list  340   a,  which enables the TV receiver  4  to promptly display a newest program schedule in response to a request from the user. 
     FIG. 9 is a flow chart showing an exemplary operation of an interrupt subroutine executed by the controller  225  in response to an interrupt from the communication IF  228 . If the communication IF  228  receives an alerting call, the IF  228  issues an interrupt signal to the controller  225 . The flow chart of FIG. 9 is identical to the part of the flow chart of FIG. 7A which part comprises the steps  444 ,  446 ,  448 ,  450  and  452 . For this reason, the detailed description of FIG. 9 will be omitted. 
     However, it is noted that once the time and date of emergency broadcast and the relevant channel is saved in a predetermined location in step  452  of FIG. 7A or  9 , the controller  225  monitors the current time periodically. If the controller  225  detects that the saved time and date is reached, the controller  225  turns on the switches  231  and  232  selecting the saved channel to receive the emergency broadcast. 
     Though the second transmission media  5  is used only for emergency broadcast in the above example, the second transmission media  5  may be also used for informing the TV receivers  4  of a change of any program. 
     In the operation of the TV transmitter  2  shown in FIG. 4, the steps  408  through  414  has been used to ensure that the interval between adjacent times to change  328  is not less than the preset period. Instead of doing this, the steps  408  through  414  may be eliminated from the flow chart of FIG. 4, and the controller  225  may execute a routine shown in FIG. 10 before executing the operation of FIGS. 7A and 7B instead of simply executing the routine of FIGS. 7A and 7B at the time specified by the first time and date of the update time list  340   a.  In step  480 , the controller  225  makes a test to see if it is a time specified by the first time and date in the update time list  340   a.  The controller  225  repeats step  480  till the first time and date is reached. In step  482 , the controller  225  make s a test to see if any time and date is being deferred (or registered as deferred). If not, the controller  225  registers the first time and date as deferred by setting a flag for the first time and date or by storing the first time and date in a predetermined location in step  484 . After step  484  or if the test result is YES in step  482 , the controller  225  proceeds to step  486 , where a test is made to see if the next time and date is within a predetermined period from the first time and date being deferred. If so, then the controller  225  waits till it becomes a time specified by the next time and date in the update time list  340   a  in step  488  and then returns to step  482 . If the test result is NO in step  486 , then the controller  225  ends the operation and enters the operation of FIG. 7, that is, proceeds to step  444  of FIG.  7 A. 
     If the update time list  340   a  contains 18:00, 18:03 and 18:05 for example, and the predetermined period is 5 minutes, then the controller  225  operates in the following manner. Since no time is being deferred at 18:00, the controller  225  registers 18:00 as deferred. Since the next time 18:03 is within the predetermined period of 5 minutes, the controller  225  waits till 18:03 at step  488 , and returns to step  482 . Since the time 18:00 is being deferred (step  482 ) and the next time 18:06 is not within 5 minutes from 18:00 ( 486 ), the controller  225  ends the operation. 
     It should be noted that the predetermined period may be set to any suitable value. 
     Displaying Program Information 
     The TV receiver  4  supports some display formats. A program time table and various program lists by category defined by the category field  323  of the program guide table are available. 
     By setting higher priorities to programs that the information provider desires to make the subscribers view, it is possible to display program information for programs with higher priorities faster than that of other programs. Doing this can increase the possibility of the higher-priority programs being viewed. 
     In the above-description it has been assumed that the nonvolatile memory  226  has enough capacity to store all of the program guide records transmitted from the TV transmitter  2 . However, the nonvolatile memory  226  may have insufficient capacity. We discuss such a case in the following. 
     In such a case, the basic strategy is to leave program guide records for higher-priority programs in the memory  226  while discarding lower priority program guide records. The value of the priority  329  field, the reception interval (detailed later), and the priorities assigned to relative positions in the program time table with respect to the cursor position (at the time of displaying a program time table) can be used as the degree of priority. 
     Reception Interval 
     In order to find the priority of each program, each program guide record  300   a  include a first reception time (T 1 ) field  331 , a reception count (Cr) field  332  and a reception interval (Ir) field  333 . T 1  is the time when the program guide record  300   a  has been first received. Cr is the number of receptions of the program guide record  300   a.  The reception interval Ir  333  is given by 
     
       
         (the current time−T 1 )/Cr. 
       
     
     It is assumed that the reception interval for a program for which only one program guide record has been received is simply given by 
     
       
         the current time−T 1 )Cr. 
       
     
     In order to keep the values Cr updated, it is necessary to increment the value of the reception count Cr each time of reception of the program guide record  300   a  regardless of whether the program guide record  300   a  has been altered or not. The flow chart of the controller&#39;s operation in which the reception interval Ir is used as the degree of priority is obtained by inserting a step  490  of FIG. 11 between the steps  454  and  460  and replacing the step  456  with a routine of FIG.  12 . 
     In FIG. 11, the controller  225  increments the value of the Cr field  332  of the record  300   a  in the program guide table of FIG. 8 in step  490  after step  454 , and proceeds to step  560 . 
     In FIG. 12, the controller  225  makes a test in step  491  to see if there is a space for storing the received program guide record in the nonvolatile memory  226 . If so, the controller  225  adds the record to the program guide table in step  494  and ends the operation. Otherwise, the controller  225  makes a test in step  492  to see if there is any record whose priority (reception interval Ir in this specific example) is lower (shorter in this example) than a predetermined value. It is noted that the reception interval Ir for a new program guide record may be set to any suitable value. If such a record is not found, then the controller  225  ends the operation. If such a record is found, the controller  225  discards the found record in step  493 , and proceeds to step  494 , where the received program guide record is added to the program guide table. 
     In the above example, programs of a longer reception interval is given a higher priority. This is because since it takes a longer time to receive a program guide record of a longer reception interval, it is preferable to make an arrangement to cause such program guide records as have longer reception intervals to be stored in the nonvolatile memory  226  by giving such the program higher priorities. However, programs of a longer reception interval may be given a lower priority. 
     Though the reception interval Ir is used as it is as the degree of priority, the degree of priority P may be defined as 
     
       
         
           P=A×Ir, 
         
       
     
     where A is an arbitrary constant. Alternatively, the degree of priority P may be defined as 
     
       
         
           P=A/Ir. 
         
       
     
     Thus, causing program guide records of higher priorities to be stored in the nonvolatile memory  226  enables program information for higher-priority programs to be displayed first. 
     If a plurality of lower-priority records are found in step  492 , various way of processing can be considered. All of the found record may be discarded. The one of the found records that has not been accessed for the longest time may first discarded. Or, The one of the found records that has been accessed the least frequently may first discarded. In this way, a judgement may be made by a combination of the degree of priority, the last access time  334  and the access frequency  335 . 
     Though the reception intervals Cr have been actually calculated by the controller  225  of the TV receiver  4 , the reception interval Cr,i.e., the degree of priority may be calculated or set by the TV transmitter  2  side and transmitted together with the program guide records to the TV receivers  4 . 
     In the above-described embodiment, a priority has been set to each program (or each program guide record). However, a priority may be set to each of the table types as shown in FIG.  13 . In this specific example, table types PAT, PMT, NIT, SDT and schedule EIT are given priorities of  1 ,  2 ,  5 ,  10  and  20 , respectively. 
     Displaying a Program Time Table Based on Readiness 
     According to the principles of the invention, once a frame of program time table is displayed, readiness is assigned to each element of a matrix formed by the channels available in the TV broadcasting system  1  and the hours for which program information is supplied by the TV transmitter  2 . FIG. 14 is a diagram showing an exemplary readiness map defined when the user issued a program time table display command at a time from 3 p.m. and to 4 p.m. of December 17. In FIG. 14, numerals written over respective columns correspond to channel numbers assigned to the available channels (36 channels in this example). The vertically arranged expressions indicate time and date for 48 hours from 3 p.m. In this specific example, programs of channels  1  through  8  from 12/17 3 p.m. to 12/18 2:59 p.m., i.e., programs in a range defined by a white box are first displayed in a frame. The first displayed programs have a readiness of  4 . Dotted areas  502  have a readiness of  3 . Slashed areas  503  have a readiness of  2 . Hatched areas have a readiness of  1 . 
     FIG. 15 is a flow chart showing an exemplary operation of displaying a program time table in accordance with the principles of the invention. In step  601 , the controller  225  displays a frame of program information in a predetermined range. In step  602 , the controller  225  applies a preset readiness pattern ( 501  through  504  in this specific example) to the current channel-time matrix to form a readiness map as shown in FIG.  14 . the controller  225  collects detailed information  337  (FIG. 8) for the programs of readiness  4 , and basic information for programs of the other readiness. It is assumed that the controller  225  usually collects data items  321  through  329  (basic information) for each program guide record  300   a  to save memory. In step  604 , a test is made to see if the user has made a request for displaying detailed information  337  for any program. If so, the controller  225  displays the requested detailed information  337  in step  605 . After step  605  or if the test result is NO in decision step  604 , then the control is passed to step  606 , where a test is made to see if any new display area is specified. 
     If so, the controller  225  displays a frame of program information in the specified display area in step  607  and moves the preset readiness pattern  501  through  504  to the new display area to form a new readiness map as shown in FIG. 16 in step  608 . In FIG. 16, the display area is set for the channels  7  through  14  and for hours from 12/17 19:00 to 12/18 7:59. Then, the controller  225  makes a test to see if the user has issued a termination command in step  609 . If so, the controller  225  ends the operation. If the test result is NO in step  606  or  609 , the controller  225  returns to step  603 . 
     The readiness pattern may be in any form and have more readiness values. 
     Modifications 
     In the above-described embodiment, the time to change  328 , the create/change time and date  327  and the priority  329  have been set to each program or program guide record. However, the time to change  328 , the create/change time and date  327  and the priority  329  may be set to each table type in a manner shown in FIG.  13 . 
     If each of the transport streams carries program information for channels of the other transport streams as well as own channels, the user can get newest program information even during viewing any channel. 
     Many widely different embodiments of the present invention may be constructed without departing from the spirit and scope of the present invention. It should be understood that the present invention is not limited to the specific embodiments described in the specification, except as defined in the appended claims.