Teletext receiver with page up and page down functions
BACKGROUND OF THE INVENTION 
     This invention relates generally to teletext (TTX) systems and particularly to teletext systems having multiple page memory storage. Teletext systems, wherein primarily textual information is transmitted during the vertical blanking intervals of a television signal, have been known for some time. Such systems have been slow to gain popularity in the United States, although they have been in use in Europe for a number of years. To obtain the benefits of teletext transmissions, a teletext processor or decoder is required. Generally, processor circuitry is incorporated into a television receiver to enable acquisition of the transmitted data and the storing of that data in a teletext page memory. The teletext signal format involves a series of magazines each having up to 100 pages that are transmitted one after the other in a cyclical manner. TTX data is acquired by means of user entered magazine and page number requests. When a circulating page of TTX data has been acquired, the information is displayed on the cathode ray tube (CRT) in the viewer&#39;s television receiver. Some teletext processors have relatively large memories and are capable of acquiring a plurality of pages of TTX data. In U.S. Pat. No.  4,388,645, multiple page storage of TTX data is provided in a cable system. In that arrangement, the cable head-end is provided with means for acquiring a multiplicity of teletext pages and for arranging for their appropriate transmission at predetermined times. 
     In the publication, Digit 2000 VLSI Digital TV System, Edition 1984/5, by Intermetall Semiconductors of ITT, which publication is hereby incorporated by reference, a teletext processor unit (TPU) is described in which up to eight pages may be acquired in response to appropriate user input commands. Minimum acquisition delay would be experienced when reading through the pages of TTX data that are in the memory. 
     The system described in the Digit 2000 publication thus provides for easy and fast &#34;paging&#34; among a group of user preselected teletext pages. The system of the U.S. Pat. No. 4,388,645 patent provides for retransmission of previously acquired pages of TTX data based upon a time code inserted by the cable operator, when the data is acquired. The present invention is directed to a system in which responsive to a user request for a desired page of TTX data, a number of predetermined adjacent pages of TTX data are automatically acquired and placed in memory and are readily available for viewing in response to simple page up and page down commands. 
     OBJECTS OF THE INVENTION 
     A principal object of the invention is to provide a novel teletext system. 
     Another object of the invention is to provide an automatic teletext system in which access time between adjacent teletext pages is minimized. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects and advantages of the invention will be apparent upon reading the following description in conjunction with the drawings, in which: 
     FIG. 1 is a simplified block diagram of a television receiver and TTX system of the prior art; 
     FIG. 2 is a simplified block diagram of the teletext processor constructed in accordance with the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In FIG. 1, a television signal tuner receives signals from an antenna or the like and supplies them to an IF amplifier 12 where they are detected and processed by well-known means (not shown). The output of IF amplifier 12 is supplied to a video CODEC unit (VCU) 14 which in turn supplies a CRT 16. A TTX processor 18 is bidirectionally coupled to VCU 14 and is in turn controlled by a microprocessor based central control unit (CCU) 20. CCU 20 controls operation of tuner 10, IF amplifier 12 and other portions of the television receiver, which have been omitted for simplicity. A keyboard (KB) 22 is coupled to CCU 20 and enables a user to control the functioning of the television receiver and TTX processor. It will be appreciated that keyboard 22 may be supplemented by a remote control system for permitting control of CCU 20 by a user from a distance. The FIG. 1 depiction is essentially that of the VLSI Digit 2000 Digital TV System of the Publication mentioned above. 
     In FIG. 2, TTX processor 18 is indicated by the dashed line box. It includes a memory 28 which is a 64 kilobyte DRAM (dynamic random access memory). The DRAM is organized into a TTX sector memory 30 that includes sectors numbered 0-7 and a page request register 32 for flagging the sectors in sector memory 30 and their contents. A block 31, indicating the flags, is shown between memory 30 and page request register 32, for convenience in description. Page request register 32 includes a plurality of sections 32a-32f, and sectors 32x and 32y which are indicated in dashed lines. Sections 32a-32f are used with the present invention to store a sequence of contiguous pages of TTX data. Sections 32x and 32y are used for other purposes not involved with this invention. The flags in block 31, labelled Fa-Ff and Fx and Fy correspond to the respective sections in the page request register. A display register 34 is interconnected by a bidirectional communications bus with page request register 32. DRAM 28 is also connected via a bidirectional communications bus 25 with a teletext processor unit (TPU) 26 which in turn is connected to CCU 20 by a bidirectional communications bus 27. Keyboard 22 includes buttons 21 and 23 for activating page up and page down functions, respectively. A ROM 24 is coupled to CCU 20 and supplies a program for operating the teletext system in accordance with the invention. 
     In operation, in response to an acquisition signal from the keyboard 22, the teletext processor sets the appropriate flag in block 31, acquires the page of teletext data that has been requested and places the page number in the page request register. In accordance with the inventive method, appropriate additional flags are set and the teletext system automatically acquires five other pages of teletext data, which are all loaded into sector memory 30. The pages acquired thus form a contiguous sequence of pages of TTX data. Assuming the requested page is P, the system acquires P-1, P, P+1, P+2, P+3 and P+4. For example, if teletext page number 102 is requested, flag Fe is set and flag Ff, corresponding to the adjacent lower page 101 and flags Fa-Fd, corresponding to the four adjacent higher pages 103-106 are set. The corresponding pages of TTX data are then acquired and stored in sector memory 30. As illustrated, the page numbers are identified in the page request register with the requested page 102 occupying section 32e, page 101 occupying 32f, page 103 occupying 32d, etc. Simultaneously, CCU 20 stores information in its memory to indicate the page currently being displayed (page 102), the high page number (106) and the low page number (101) in the sector memory. Thus, in response to a request for page 102, pages 101-106 are acquired, and page 102 is displayed for viewing by the user. (It is not necessary that all pages be completely acquired before display of page 102, however.) 
     The inventive method is designed to accommodate normal viewer reading habits and acquires four pages of TTX data following the requested page and only a single page preceding the requested page. Normally, a user will read the selected page and &#34;page forward&#34; to read additional pages. Only occasionally will a viewer want to refer back to a prior page. Paging is accomplished by the viewer initiating the page up or page down function either by depression of keys 21 and 23, respectively, on keyboard 22 or by sending an appropriate command via a remote control unit (not shown). In general, the adjacent teletext page will already be in memory 30, and display of that page will occur very rapidly. If, for example, a page up signal is sent, display register 34 reflects page 103 for display on the CRT screen. The low page number in CCU 20 is incremented from 101 to 102, the high page number in CCU 20 is incremented from 106 to 107. The corresponding flags are cleared and set and page number 101 in section 32f is replaced by the next higher page number in the sequence which is 107. The TTX data corresponding to the replaced page number (101) is overwritten as the data corresponding to new TTX page 107 is acquired and stored in the memory in that location. A further page up request would result in number 102 in section 32e being replaced by number 108, display register 34 indicating information corresponding to section 32c and the incrementing of the low and high page numbers in CCU 20. The TTX page of data in memory 30, corresponding to TTX page 102, is replaced with data corresponding to TTX page 108, as that data is acquired. 
     A page down request proceeds in the opposite direction with the page number 106 in section 32a being replaced with number 100. The high page, low page and displayed page information in CCU 20 is incremented or decremented as the page up and page down commands are executed. 
     Under certain circumstances, the user may request TTX pages, through use of the page up and page down commands, at such a rate that the requested page has not yet been acquired. Rather than displaying erroneous data, the software routine provides for jumping out to its normal direct access mode and the system reinitializes itself with the desired page number being treated as a direct request for that page number. This is not perceptible to the user. The software routine also accounts for the &#34;wrap around&#34; in page numbers since the page numbers are restricted to 0-99. The software routine for performing the inventive method is attached hereto as an appendix. 
     In summary, on direct access, the variables, i.e. high page number, low page number and the displayed page, are established in CCU 20, the appropriate flags are set in the memory and the teletext system acquires all of the teletext data encompassed between the high and low page numbers. The acquired page numbers are loaded into the page request register. In response to a page up command, the high page number is incremented by one, the low page number is incremented by one, the new sector memory location for the one page of TTX data that is to be acquired is calculated and the display register is incremented by one. An opposite routine is followed for the page down command with the high and low page numbers being decremented by one. It will be appreciated that during the page up and page down functions, only one page of TTX data is replaced in the sector memory. That page of TTX data is replaced with the new page of TTX data. ##SPC1##