`
`United States Patent
`§©3,886,302
`(tt)
`Kosco
`[45] May 27, 1975
`EwwApee,
`
`119
`
`[75]
`
`[54] CLOSED CIRCUIT TELEVISION MODEM
`ABSTRACT
`[57]
`SHARING SYSTEM
`A system for controlling CATV program viewing in a
`Inventor: Thomas J. Kosco, Harbor City,
`:
`wT
`.
`plurality of modes of operation. In a first mode of op-
`Calif.
`eration, a downstream digital transmission causes con-
`trol means to developfirst binary data for comparison
`[73] Assignee: Hughes Aircraft Company, Culver
`in a comparator with selected-channel code data from
`City, Calif. channel meansto enableafirst circuit to allow a first
`
`Jan. 28, 1974
`[22]
`Filed:
`or second category program to be selected and re-
`ceived by a subscriber during a predetermined tempo-
`[21] Appl. No.: 437,410
`rary periodof time. In a second mode ofoperation the
`enabling of a secondcircuit by the subscriberwill only
`.
`:
`:
`.
`cause the control means to be enabled if the sub-
`scriber is authorized toreceive that selected first cate-
`80ry program. In a third mode of operation the en-
`abling of the second circuit by the subscriber will en-
`program to be received. In a fourth mode ofoperation
`able a third circuit to allow a selected second category
`r
`.
`the selection of a third category program by the sub-
`scriber will enable a fourth circuit to allow that se-
`lected third category Program to
`be
`received.
`MODEM sharing networks are provided in the cable
`system interconnecting a local processing center and
`the various subscriber terminals. Each MODEM shar-
`ing network has modulation and demodulation cir-
`cuitry, and ability to handle about twelve subscriber
`terminals.
`
`[$2] U.S. Ch oo. 178/5.1; 325/308; 178/DIG. 13
`[SU]
`UMt. Chee cccccccccccccccccsevessseteeeeeecee, H04n 1/44
`[58]
`Field of Search ....... 325/308; 178/5.1, DIG. 13
`be]
`References Cited
`UNITED STATES PATENTS
`3,786,424
`1/1974 McVoyet al................ 178/DIG. 13
`3708cap
`S074 Wenetal pera
`
`3,806,814
`4/1974 Forbes... 178/DIG. 13.
`
`Primary Examiner—Maynard R. Wilbur
`Assistant Examiner—S. C. Buczinski
`Attorney, Agent, or Firm—W.H. MacAllister; Martin
`E. Gerry
`
`
`
`8 Claims, 10 Drawing Figures
`
`Yo Subscriber's
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`and
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`Button
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`
`Poy TV Request
`Chonnel Code
`
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`Eaee
`Subscriber Terminal 25
`.
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`PMC Exhibit 2108
`Apple v. PMC
`IPR2016-00753
`Page 1
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`PMC Exhibit 2108
`Apple v. PMC
`IPR2016-00753
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`
`
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`Apple v. PMC
`IPR2016-00753
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`PMC Exhibit 2108
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`IPR2016-00753
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`PMC Exhibit 2108
`Apple v. PMC
`IPR2016-00753
`Page 3
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`IPR2016-00753
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`PMC Exhibit 2108
`Apple v. PMC
`IPR2016-00753
`Page 4
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`Page 4
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`PMC Exhibit 2108
`Apple v. PMC
`IPR2016-00753
`Page 5
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`PMC Exhibit 2108
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`IPR2016-00753
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`Apple v. PMC
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`PMC Exhibit 2108
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`Apple v. PMC
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`IPR2016-00753
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`Apple v. PMC
`IPR2016-00753
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`

`3,886,302
`
`1
`CLOSED CIRCUIT TELEVISION MODEM
`SHARING SYSTEM
`
`BACKGROUND OF THE INVENTION
`
`This invention relates to CATV systems and particu-
`larly to a system for controlling CATV program view-
`ing in several modes of operation having a common
`MODEMsharing network for a plurality of subscriber
`terminals.
`Although the term “CATV,” as used herein, origi-
`nally meant Community Antenna Television it has
`come to represent a much broader field of communica-
`tions. Within the past decade additional services have
`been proposed and in some cases actually provided by
`some CATV systems operators.
`In the realm of one-
`way communicatinos (i.e., from a central transmitter to
`the subscribers), services such as AM and FM radio
`programs, weather broadcasts and locally originated
`television programs have been provided as part of the
`CATV services. With the availability of two-way cable
`distribution networks a vast numberof additional com-
`munications needs can be served. The availability of
`upstream communications channels allows the sub-
`scribers of a CATV system to be surveyed orpolled for
`viewing habits or billing and,
`in addition, allows the
`subscribers to obtain services which are unrelated to
`television. Therefore, although the term “CATV” is
`used herein it should be noted that the term includes
`two-way communications on a much broaderscale but
`which retains television programming as an important
`function.
`In the past, many systems have been proposed for se-
`lectively transmitting various television programs to
`subscribers. In one type of system a transmittingstation
`utilizes a coder unit to scramble the video and sound of
`the television programs so that conventional television
`receiver cannot receive anintelligible signal. The signal
`being received is so distorted or jittered that it cannot
`be viewed normally. However, when the television re-
`ceiver is equipped with a decoder to unscramble the
`coded signal, normal video and sound can be received.
`The use of the decoder to unscramble the coded signal
`is generally recorded for billing the subscriber at some
`later time.
`In a second type of system, a transmitting station fur-
`nishes each ofits subscribers with a list of films which
`it possesses, with each film having a specific selecting
`signal. Uponselecting a film from thelist, a subscriber
`actuates a control which turns on his television set and
`searches for a free channel on one ofa plurality of ca-
`bles connected to a distribution box which is coupled
`between the subscriber's location and the transmitting
`station. When a free channel is found, a signal informs
`the subscriber that he is connected with the transmit-
`ting station through a free channel which has been lo-
`cated. At that time the subscriber actuates a selector
`control which transmits through the free channel of the
`cable complex to the transmitting station a signal corre-
`spondingto the film which the subscriber has selected.
`The station then automatically selects the required
`film, starts this film and causes a high frequencytrans-
`mitter to transmit the television program via the free
`channel to the subscriber’s television set. At the com-
`pletion of the program, the transmission stops automat-
`ically and the television receiver is switched off auto-
`matically.
`
`5
`
`20
`
`30
`
`35
`
`40
`
`45
`
`50
`
`2
`In a third type of system a private coaxial distribution
`network allows a transmitting station network to simul-
`taneously transmit a plurality of unscrambled subscrip-
`tion television (TV) programs to each of a plurality of
`subscribers. EAch subscriber has a five-position switch
`on a special converter, which is coupled to the coaxial
`network and to the subscriber’s television antenna. In
`one position of the converter switch, free television is
`received via the subscriber's television antenna in a
`conventional manner. In a second position of the con-
`verter switch, voice and music can be received through
`the loudspeaker of the subscriber’s TV set via the cable
`distribution network. In each of the last three positions
`of the converter switch, a different pay television chan-
`nel can be received. It is important to note that the only
`television programsutilized in this system are pay tele-
`vision programs, since the coaxial network is effec-
`tively disconnected if the subscriber wants to receive
`free TV programs from his antenna. A response code,
`indicating the position of the converter switch, is sent
`back to the transmitting station so that the subscriber
`may be billed for watching any pay TV programs.
`In a fourth type of system each ofa plurality of sub-
`scribers is periodically interrogated from a central of-
`fice during a preselected time slot. If a subscriber actu-
`ates a control on his subscription TV receiver set so
`that a channel he desires to watch maybe utilized, a
`“yes” signal is sent back in response to the interroga-
`tion to indicate that a particular pay TV channel is
`being utilized or watched. A “no” response, of course,
`indicates that the particular pay TV channel
`is not
`being viewed. The yes responses are ultimately used to
`bill the subscribers.
`In all of the above types of systems, some positive ac-
`tion by the subscriber must be undertaken to enable a
`pay TV program from the transmitting station or cen-
`tral office to be viewed by the subscriber. When the
`subscriber has undertaken that positive action, whether
`by setting up a decoder, positioning a switch or actuat-
`ing a control, he will be subsequently billed for watch-
`ing the selected TV program because it is a pay TV pro-
`gram. As a result, the above types of systems do not
`provide a period of time during which a pay TV pro-
`gram may be previewed without charge, and then auto-
`matically disabled unless the subscriber has taken the
`required action to see the balance of the program for
`a fee. Furthermore, none of the above types of systems
`provide restricted pay TV programs for which the sub-
`scriber must be eligible to watch, as well as be willing
`to pay.
`None of the aforesaid systems have a common
`MODEM (modulator - demodulator) network as an in-
`tegral portion of the cable distribution subsystem,
`shared amonga plurality of subscriber terminals. Con-
`sequently, none of the systems make useofrelatively
`inexpensive, ordinary telephone transmission lines for
`interconnection of the MODEM networks with several
`subscriber terminals.
`
`SUMMARY OF THE INVENTION
`
`f
`
`i
`
`Accordingly, it is a general objective of this invention
`to provide a common MODEM sharing network, within
`the cable distribution subsystem shared amonga plural-
`ity of subscriber terminals. It is a further general objec-
`tive of this invention to interconnect data encoders and
`decoders of the MODEM sharing network BHREIESEiit 2108
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`3,886,302
`
`20
`
`4
`3
`FIG. 3 shows in tabular form one five-bit channel
`nary telephone transmission lines and thereby reduce
`code which may be used in the control of subscription
`system cost and increase economyof operation.
`TV channels;
`Another object of this invention ts to provide a sys-
`FIGS. 4 and§illustrate waveforms useful in explain-
`tem wherein at least one subscription program may be
`ing the operation of the controllogic circuit 47 of FIG.
`previewed without charge by the subscriber during at
`2,
`least one predetermined preview period.
`FIG. 6 is a schematic block diagram of the control
`Another object of this invention is to provide a sys-
`logic circuit 47 of FIG. 2;
`tem for allowing a restricted subscription program to
`FIG. 7 is a schematic block diagram of a two-way
`be received only by membersof a predetermined group
`CATVsystem incorporating the headend of the system
`of viewers.
`interconnected to the cable distribution subsystem
`Another object of this invention is to provide a sys-
`which includes the MODEMsharing network,
`tem which will enable a subscriber to selectively re-
`FIG. 8 is a schematic block diagram showinga typical
`ceive nonrestricted subscription programs, authorized
`subscriber terminal as used with the MODEM sharing
`restricted subscription programs, free previews of sub-
`network, and telephone transmission line and coaxial
`scription programs, and free programs.
`cable interconnecting the MODEM sharing network
`A further object of this invention is to provide a sys-
`with the typical subscriber terminal,
`tem which enables an authorized subscriber to switch
`FIG. 9 is a schematic block diagram of the same sys-
`away from a previously purchased subscription pro-
`tem as in FIG. 7 except that additionally a premium and
`gram and subsequently return to it without incurring an
`restricted TV control circuit has been added thereto,
`and
`additional charge.
`Briefly, a novel system is provided for controlling
`FIG. 10 is a schematic block diagram of the same
`CATVprogram viewing in a plurality of mode of oper-
`subscriber terminal as in FIG. 8 except that a key con-
`ation. In a first mode of operation, control logic enables
`trol and subscription TV request button has been
`25
`added thereto.
`a video register to causeafirst circuit to enable an out-
`put circuit to allow a subscriber to previewat least one
`DETAILED DESCRIPTION
`subscription TV program during a predeterminedpre-
`view period of time without charge, if the subscriber
`selects that program during the preview period.
`In a
`second mode of operation, the subscriber will only be
`allowed to receive a selected restricted subscription
`program, if he enables a second circuit and the control
`logic is enabled by a signal indicating that the sub-
`scriber is authorized to watch that restricted subscrip-
`tion program. In a third mode of operation, the sub-
`scriber may select a non-restricted subscription pro-
`gram by enabling the second circuit which,
`in turn,
`causes a third circuit to enable the output circuit to
`allow the non-restricted subscription program to be re-
`ceived. In a fourth mode of operation, the subscriber
`mayselect a free program by enabling a fourth circuit
`to enable the output circuit to allow the free program
`to be received.
`The novel system includes the head end, wherein the
`local processing center is located, and connected by
`means of coaxial cable to a MODEM sharing network.
`The MODEM sharing network is connected by means
`of ordinary telephone transmission lines to a plurality
`of subscriber terminals for transmitting data informa-
`tion leaving only television channel to be transmitted
`on the coaxial cable through the MODEMsharing net-
`work on a preselected basis to a particular subscriber
`terminal.
`
`Referring to the drawings, FIG. 1 discloses a two-way
`CATV (cable television) system which incorporates
`the invention. Television (TV) and radio broadcastsig-
`nals transmitted through the air are received by a plu-
`rality of elevated receiving antennas 11a through IIn
`for subsequent processing by a plurality of video pro-
`cessors 12a through 12n which are located at a hea-
`dend site 13. Signals from a local origination studio 14,
`which may be located at some distance from the hea-
`dendsite 13, are supplied for subsequent processing to
`a video processor 15 at the headend site 13. A local
`processing center (LPC) 16 at the headend site 13 in-
`cludes a computer 17. The LPC 16 allows two-way
`communications between the subscribers and the hea-
`dend site 13. Each of the outputs of the LPC 16 and
`video processors 12a through 12” and 15 is frequency
`multiplexed onto a main trunk line 18 with the other
`outputs via its associated directional coupler 19. In a
`downstream transmission the television and radio sig-
`nals might occupy a large part of the frequency range
`from 54 MHz to 270 MHz, for example. A carrier cen-
`tered about 110 MHz, for example, might accommo-
`date the downstream digital data. The combinedsignals
`are transmitted downstream from the headendsite 13
`to a plurality of subscriber terminals. In an upstream
`transmission, digital data responses in, for example, the
`21 to 25 MHzfrequency range with a center frequency
`of 23 MHz and video transmissions in, for example, the
`5to 21 MHz frequency range may be respectively re-
`ceived by the LPC 16 and video processor 15.
`It is understood, of course, that the frequency ranges
`mentioned above are for the purpose of explanation
`only and should not be understoodto limit the scope of
`the present invention. The exemplary frequencies men-
`tioned above correspond roughly to the bandwidths of
`presently available commercial CATV equipment.
`The downstream transmission of the video band and
`digital signals goes through the main trunk line 18 and
`is split off into a distribution network 20 until it is chan-
`neled through a cable drop line 21 into a filter and
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`BRIEF DESCRIPTION OF THE DRAWINGS
`These and other objects, features and advantages of
`the invention, as well as the invention itself, will be-
`come more apparent to those skilled in the art in the
`light of the following detailed description taken in con-
`sideration with the accompanying drawings wherein
`like reference numerals indicate like or corresponding
`parts throughout the several views wherein:
`FIG.
`1
`is a schematic block diagram of a two-way
`CATV system,
`FIG. 2 is a schematic block diagram of the premium
`and restricted TV control circuit of FIG. 1;
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`combiner circuit 23 located within a subscriber termi-
`nal 25. The filter and combiner circuit 23 separates the
`digital data from the video band and routes the televi-
`sion and radio signals to a converter 27 and the digital
`data to a downstream commandreceiver and decoder
`29. The downstream command receiver and decoder
`29 may include a demodulator circuit (not shown) to
`remove the transmitted carrier frequency, a Manches-
`ter decoder (not shown) to separate input clock pulses
`from a digital code, and a decoder (not shown) to ex-
`tract channel data as well as any one of a group of com-
`mands such as preview enable, video enable, and video
`disable. The commands, channel data and input clock
`pulses are applied to a premium and restricted TV con-
`trol circuit 31 which controls the “on” and “off” status
`of the converter 27. In an on condition, the converter
`27 is allowed to pass a selected video channel within
`the video band to a subscriber’s TV antenna terminals
`for viewing. In an off condition, the converter is dis-
`abled, thereby preventing any video from being applied
`to the subscriber’s TVset. while the output of the con-
`verter 27 is shown and described as going to the sub-
`scriber’s TV set, it should be obvious that the converter
`27 may be an integral part of the subscriber's TV set
`rather than ancillary to it.
`The operation of the premium and restricted TV con-
`trol circuit 31 is controlled from a console 33 and has
`four modes of operation. At the console 33 a channel
`selector switch 35 determines which TV channel is de-
`sired by the subscriber, while a fine tuning control 37
`allows for a close adjustment in the channel tuning. The
`channel selector switch 35 generates, for example, a
`five-bit channel code which is applied to the control
`circuit 31, as well as to a digital-to-analog (D/A) con-
`verter 39, to indicate the selected TV channel. A digital
`signal from the fine tuning control 37 is also applied to
`the D/A converter 39. The D/A converter 39 combines
`the digital information from the channel code and from
`the fine tuning control 37 and generates an analog con-
`verter tuning signal which is used to tune a varactor
`(not shown) in the converter 27, thereby allowing sig-
`nals from the finely tuned selected channel to be ap-
`plied from the converter 27 to the subscriber’s TV set
`at a predetermined output frequency.
`In a first mode operation, the computer 17 in the
`LPC 16 transmits a preview enable command down-
`stream to the control circuit 31 to allow a subscription
`TVprogram to be previewed on a predetermined chan-
`nel. Any subscriber mayview the subscription TV pro-
`gram being previewedif he positions the channelselec-
`tor switch 35 to that channel within the preview period.
`If the subscriber selects the channel in which a sub-
`scription TV program is being previewed, he will be al-
`lowed to see that TV program for a predetermined
`length of time without charge. If the subscriber desires
`to watch the completionof the previewed program, he
`would have to insert a key in a key control unit 41
`which enables a subscription TV request button 43 to
`be pressed. If the subscriber presses the button 43 be-
`fore, or even after, the completion of the preview pe-
`riod, he will be allowed to watch therest of that pre-
`mium program and will be billed accordingly. By press-
`ing the button 43, a pay TV request signal is generated
`by the control circuit 31 and applied to an upstream
`command formatter and transmitter unit 45 to whichis
`also applied the channel code from the channelselec-
`tor switch 38, The formatter and transmitter unit 45
`
`6
`combines the pay TV request signal and channel code
`with an internally generated station address code. This
`combination ofsignals is then modulated ontothe pre-
`selected upstream carrier frequency. This upstream
`carrier is applied through the filter and combiner unit
`23 and transmitted upstream through the cable drop
`line 21, the distribution network 20 and the main trunk
`line 18 to the LPC 16 whereit is processed by the com-
`puter 17, The computer 17 records the subscriber's
`channel address and the channel selected for billing
`purposes and then initiates a downstream digital trans-
`mission at the center frequency of 110 MHz which is
`ultimately decoded by the receiver and decoder unit 29
`as a video enable command. This video enable com-
`mand confirms that the subscriber has been billed and
`allows the control circuit 31 to keep the converter 27
`turned on after the termination of the preview period
`if the pay TV request was made before the completion
`of the preview period, or turns on the converter 27 if
`the pay TV request was made after the termination of
`the preview period.
`In a second modeof operation, the subscriber may
`initiate a request to receive a restricted category sub-
`scription program. This is accomplished at the console
`33 by the subscriber inserting his keyin the key control
`circuit 41 and pressing the subscription TV request
`button 43 which enables the control circuit 31 to gen-
`erate the pay TV request signal. However,
`the sub-
`scriber will not be immediately allowed to receive the
`restricted program. The pay TV request signal will be
`sent upstream to the LPC 16,and the computer 17 will
`search its memory to see if the subscriber is one of the
`personsonits restricted list of persons authorized to re-
`ceive the requested program. Restrictedlists, for exam-
`ple, may be respectively composed of groups of doc-
`tors, groups of lawyers, or other groups of subscribers
`sharing a common interest. Restricted programs there-
`fore might comprise programsofinterest to only those
`selected groups of persons. For example, a medical op-
`eration may be only useful to doctors; lectures on legal
`strategies, developmentsortraining courses would only
`be of interest to the legal profession; or police tactics,
`such as criminal detection techniques orriot or crowd
`control, would only be of interest to law enforcement
`officers. In the event the computer 17 finds the termi-
`nal address of the subscriber on its restricted autho-
`rized viewer list for that type of program, it will trans-
`mit downstream to the subscriber terminal 25 a video
`enable command which will allow the controlcircuit 3]
`to process the channeldata so that the converter 27 is
`placed in an on condition to allow the subscriber to re-
`ceive the restricted program. Of course, if the subserib-
`er’s terminal address is not on the computer's autho-
`rized viewerlist, no video enable command is sent to
`the subscriber terminal 25. Under this mode of opera-
`tion therefore, only previously authorized persons can
`receive restricted category programs.
`In a third mode of operation, a subscriber can gain
`immediate access to a nonrestricted category subscrip-
`tion program byinserting his key in the key controlcir-
`cuit 41 and pressing the subscription TV request button
`43. This operation will enable the control circuit to im-
`mediately turn on the converter 27 and therefore allow
`the selected nonrestricted subscription program to be
`received without delay. As described in the second
`mode of operation, the depression of the subscription
`TV request button 43 enables the control circuit 31 to
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`generate a pay TV request signal which is transmitted
`lines 61 through 68 of the decoder 59 represent the re-
`upstream to the LPC 16. Since a nonrestricted program
`stricted or premium subscription channel that the sub-
`is selected by the subscriber, the LPC 16 will automati-
`scriber hasselected. At this time, a | state at anyof the
`cally send, during its subsequent operation, a video en-
`outputs 61 through 68 indicates that a subscription,
`able signal to confirm the billing and to keep the con-
`and not a free, channel has been selected by the sub-
`verter 27 turned on. It should be noted that the sub-
`scriber. A 1 state from either of the outputs 61 or 62
`scriber will still receive the nonrestricted subscription
`designates the selection of a restricted channel. A |
`program even if a video enable signal is not transmitted
`state from anyof the outputs 63 through 68 designates
`from the LPC 16,
`the selection of a premium, or nonrestricted channel.
`The computer 17 causes the LPC 16 to send a video
`The outputs 31 through 58 of the video register 49
`disable signal to the control circuit 31 to turn the con-
`are respectively compared with the outputs 61 through
`verter 27 off at the completion of the restricted cate-
`68 of the subscription channel! decoder 59 in respective
`gory program of the second mode of operation; at the
`AND gates 71 through 78 contained in a channel com-
`completion of the nonrestricted categary program of
`parator 79. Each of the AND gates 71 through 78 in the
`the third mode of operation; or at the completionof the
`comparator 79 has its output coupled to a different
`preview period of the first mode of operation,
`if the
`input of an OR gate 81. When the channelselected by
`subscriber has not actuated the key control 41 and re-
`the subscriber is one of the enabled channels stored in
`quest button 43 within the preview period. It should be
`the video register 49, the AND gate in the comparator
`noted at this time that both restricted energy category
`79 associated with the selected and enabled channel
`or nonrestricted category programs may be previewed
`develops a binary | output whichis applied through the
`during the first mode of operation.
`OR gate 81, then through another OR gate 83 to one
`In a fourth mode of operation, if the channel selector
`input of an AND gate 85. A second input to the AND
`switch 35 is positioned to receive a nonsubscription
`gate 85 is a TV onstatus signal from the subscriber's
`category TVprogram, or free TV program, the channel
`TV set, which is in a 1 state when the TV set is on, and
`code will enable the control circuit 31 to generate an
`in a Q state when the TV set is off. The output of the
`on control signal to turn the converter 27 on, so that
`AND gate 85 is the on/off signal that controls the on/-
`the selected free TV program maybe received at the
`off status of the converter 27 (FIG. 1). A 1] output from
`subscriber's TV set.
`the AND gate 85 turns on the converter 27, while a 0
`The premium and restricted TV control circuit 31
`output from the AND gate 85 turns off the converter
`will now be more fully discussed byreferring to FIG. 2.
`27. It
`is therefore obvious that the converter will be
`In FIG. 2, the channel data, input clock pulses, and one
`turned off when the subscriber’s TV set is turned off.
`of the preview enable, video enable, and video disable
`If, for example, the subscriber has selected that chan-
`commands are applied to a control logic circuit 47 to
`nel which causes the output 63 to go to a | state, the
`initiate the operation of the control circuit 31. The con-
`AND gate 73 will produce a | state output if the output
`trol logic 47 applies clock pulses along with a serial
`53 from the video register 49 is in an enabled I state.
`stream of, for example, eight bits of updated data to a
`The | state output of the AND gate 73 will then be
`video register 49, The video register 49 may be a shift
`passed sequentially through the OR gates 81 and 83
`register containing eight flip-flops (not shown). Each of
`and to the AND gate 85 to turn on the converter 27.
`the eight flip-flops stores one bit of the eight-bit up-
`In the fourth mode of operation, if the channel se-
`dated data in order to produce eight outputs, 51
`lected by the subscriber is such that either the A or B
`through 58. This video register 49 stores information as
`portion of the channel codeis in a | state, OR gate 87
`to which subscription TV channels have been enabled
`will be enabled to provide a | state signal which will be
`for viewing, either via a preview enable command in
`sequentially passed through the OR gate 83 and AND
`the first mode of operation or a video enable command
`gate 85 to enable the converter 27 so that the selected
`in the second or third mode of operation.
`free channel may be received by the subscriber. In ei-
`When the subscriber positions the channel selector
`ther the second or third mode of operation, both the A
`switch 35 to a channel, a five