CA1209687A - Two-way catv system with aml commands - Google Patents
Two-way catv system with aml commandsInfo
- Publication number
- CA1209687A CA1209687A CA000469597A CA469597A CA1209687A CA 1209687 A CA1209687 A CA 1209687A CA 000469597 A CA000469597 A CA 000469597A CA 469597 A CA469597 A CA 469597A CA 1209687 A CA1209687 A CA 1209687A
- Authority
- CA
- Canada
- Prior art keywords
- subscriber
- subscriber terminal
- headend
- code
- terminal
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N7/00—Television systems
- H04N7/16—Analogue secrecy systems; Analogue subscription systems
-
- G—PHYSICS
- G08—SIGNALLING
- G08C—TRANSMISSION SYSTEMS FOR MEASURED VALUES, CONTROL OR SIMILAR SIGNALS
- G08C15/00—Arrangements characterised by the use of multiplexing for the transmission of a plurality of signals over a common path
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N7/00—Television systems
- H04N7/16—Analogue secrecy systems; Analogue subscription systems
- H04N7/162—Authorising the user terminal, e.g. by paying; Registering the use of a subscription channel, e.g. billing
- H04N7/165—Centralised control of user terminal ; Registering at central
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N7/00—Television systems
- H04N7/16—Analogue secrecy systems; Analogue subscription systems
- H04N7/173—Analogue secrecy systems; Analogue subscription systems with two-way working, e.g. subscriber sending a programme selection signal
- H04N7/17345—Control of the passage of the selected programme
- H04N7/17363—Control of the passage of the selected programme at or near the user terminal
Abstract
ABSTRACT OF THE DISCLOSURE In a two-way cable television (CATV) system, multiple subscriber address codes are provided during designated vertical blanking interval (VBI) lines of the video signal transmitted from the CATV headend to a plurality of system subscriber terminals. Each subscriber terminal is provided with a decoder in which is stored subscriber unique address code for comparison with the received subscriber address codes. If there is an address match, an address match latch (AML) signal is generated for each VBI line address match. The address match signals thus generated from a multibit pulse coded downstream command signal for initiating various functions in the CATV system, e.g., acknowledging subscriber upstream requests, subscriber interrogation, power adjustment, etc.
Description
~2~
Background o~ the Invention _ _ _ This invention relates generally ~o two-way cable television (CATV) systems and is particularly directed to the transmission of data ~rom the headend to a plurality o~
s~bscribers in a two-way CATV system.
C~TV systems typically include a central master source of television programming in~ormation termed a headend which imparts programs, or groups o~ programs at different assigned ~requencies, to a network o~ cable connections which, through varlous distributian and selection network components, ultimately t~rmin~t~ in ~ branched out plurality o subscriber terminals typi~lly in residen'ce or commercial establishments. CATV
program signals are broadcast ~rom the headend to individual subscribers in a `'downstream" direction over different assigned carrier req~encies typicall~ from ~bout 50 to 450 MHz~ The CATV headend not only ~ransmits television programming informa'iol. downst~eam, but may also transmit data in the orm Q~ for example, subscriber address and authorization inormation, which allows ~he stored program de~ode authorization status of each subscriber to ~e individually controlled from the headend. Frequently, such data is encoded in the vertical 12~
blanking interval ~BI) of a transmitted CATV program signal.
The program d~c~d~ a~t~riz3ti~D ~tatus st~red in each subscrib~r' s ~erminal is co~pared with a program code also encoded in the VBI of the received CATV signal to establish whether ~r not the subscri~er is authorized for decoding the r ece i ved prog r am s ig na 1 .
In a two-way C~V system each subscriber i5 able to transmit signals back to the CA~V headend. These ~ub~crib~r-originated ~ignals may in~lude program purchasing r~u~t~, opinion poll re~ponses, and C~TV conver~er status information. ~hese upstream signals typically make use of out of band fre~uencies in the 5-32.5 MHz band. The upstream signal distribution network is in the form of a "merging tree topology"
in which the signals generated by many sources, or subscribers, converge and are transmitted on a single transmission line back to the CATV headend. Such techniques as signal multiplexing and re~ency diversity have been proposed and are utilized to accomodate large numbers of subscribers in two-way CATV systems~
Proper response to the subscriber-originated signals normally re~uires the exercise of headend control over the various remotely located subscriber terminals coupled to the CATV system. The exercise of such control requires the downstream transmission of various command signals from the headend controller to t~e su~scriber terminals.
The present invention provides a facility whereby such headend control of subscriber terminals may be conventiently realized within the environment of a prior art C~TV system employing VBI data transmission techniques. In particular, a headend command signal is transmitted during a single VBI in the form of a multibit code, each bit of which is represented ~9~
by the transmission or non-transm;ssio~ of a subscriber address code during a respective pr~deter~ined time interval of the VBI.
At the subscriber's terminal, the received address codes are processed to reconstruct the multibit code which is subsequently decoded ~or use in controlling various aspects of the terminal.
~ects o the Invention -Accordingly, it is a ba~ic object of the present invention to provide a facility for enabling headend control of a plurality of subscriber terminals in a two-way C~TV system.
It 15 a more specific object o~ the present invention to provide such a facility in the environment of an addressable CA~V ~ystem using VBI data transmission techniques.
Yet another object of the present invention is to provide such a facility in an extremely convenient and cost-ef~ective manner.
Brief Desc_ ~ion of the Drawings The appended claims set forth those novel features believed characteristic of the invention. However, the invention itsel, as well as further objects and advantages thereof, will best be understood by reference to the following detailed description of the preferred embodiment taken in conjunction with the accompanying drawings, in which:
FIG. 1 shows in block and schematic diagram form a two-way CATV system in accordance with the present invention; and ~5 FIG. 2 is a waveform diagrarn useful in explaining the operation of the system s~own in Figure 1.
Descri~tion of the Preferred Embc~imen~
~ ferring to FIG. 1, there is shown in combined schematic and block diagram form a subscriber terminal 10 for a two-way CATV system in accordance with the present invention.
12~
The system also includes a cable headend 12 coupled to each subscriber t~in~l ~O via a cable 15 and which typically includes a co~puter mu3ti~le terminals, disc drives an~ a tape backup. -These el2men~s of the ca~le headend 12 are not shown in FIG. l as they do not form a par~ of the present invention.
Downstream signals from the cable headend ~2 to indlvidual subscribers may include such infor~ation as subscriber address, program auth~rization, and market codes as well as program identifiGatlon data which is transmitted in televlsion channels h~vin~ F~uencies between abo~t S0 and 450 MHz. This data may b~ provld~d during the vertical blanking interval (VBI) o the down~ream video program~ing signals, such as in lines 10 through 13 of the V~I as shown in Table I. Although the present invention is described herein as making use of VBI lines 10-13 lS o the video programming signals for the downstream transmission of subscriber terminal commands, it is not limited to the use of these VBI lines and may utilize any portion of the vertical retrace signal including any combination of VBI lines, consecutive or nonconsecutive.
_ _ _ _ _ ._ __ _ _ . _ _ _ __ _ n-BIT
V~I Line 1~ m-BIT ADDRESS CODE AUTHORIZATION CODE
n-BIT
VBI Line 11 m-BIT ADDRESS CODE AUTHORIZ~TION CODE
n-BIT
VBI Line 1~ m-BlT hDDRESS CODE ~UTHORIZATIO~ CODE
_ _ __ _ _____ __ _ _ _ ___ __ __ VBI Line 13 x-BIT MARKET CODE y-BI~ PROGRAM TAG
The VBI occ~rs during vertical retrace o~ the raster scanned cathode ray tube ICRT~ of t~e subscriber's television receiver and co~prises ~hout 21 horizontal scanning lines.
~20~6~5P7 Referring to Table I above, in a known one-way addressable CATV
system a~ ~ bit subscriber add~e~ de an~ a related n-bit program a~ ri-z~ti~ de a~? selectively transmitted during each of lines 10~ 11 and 12 of the ~ ach address code may comprise 2~ s with each authorization code comprising 5 bits.
During line 13 of the VBI there is continuously transmitted an x-bit (e~g.ll bits) market code which defines the geographic area in which the system is operating as well as a y-bit (e.g~ 7 bits) progra-~ identification ~ode, or tag, defining the 1~ a~companying televlsion program. These downstream ~ nals ~re received by each subscriber terminal 10 and coupled by a diplex filter 14 to a decoder 18 which includes a suitable tuner tuned to an encoded CATV channel. Each received m-bit address code is compared with a unique subscriber address code stored in a programmable read only memory (PROM) 34 of decoder 18 in each subscriber terminal 10. If the received subscriber address code matches the unique~subscriber address code stored in the decoder's PROM 34, the program authori7ation code o~ the same VB I line is stored in a random access memory ~RAM) 78 in decoder 18 which defines the program decode authorization status of the subscriber. A match between the received and stored address codes will also result in the generation of an address match latch (AML) pulse by decoder 18, which pulse is provided on an output line 36 of decoder 18.
The x-bit market code received during line 13 of each VBI is compared with a subscriber terminal market code also stored in the decode~'s PROM 34. A match between the transmitted and stored market codes will enable the decoder 18 an~ also result in the gener~tion of an address match latch ~AML) pulse which is similarly provided on line 3~. A match between the ~2~
received y bit program tag ~ode and thi~ ~tored program decode au~hroization status permits the decode~ to descra~ble the received CATV video programming signal ~hich may then be viewed on the sub~criber'~ ~le~ision receiver (not shown~. The absence 5 of a match between the received program tag code and the stored program authorization status results in the video programming signal being passed on by the subscriber terminal 10 in a scrambled form. Theraafter, decoder 18 cont;nuously monitors incoming data for detecting each subsequent address or market ln cod~ match.
.~s previously mentionQA, each match between a recQived ~ubscriber address code and the unique subscriber address code stored in PROM 34 of decoder 18 results in an AML pulse on line 36. ~ccording to the present invention, the selective transmission of subscriber address codes on horizontal lines 10-13 of the VBI is used to provide a 4-bit headend command control code on line 36, each bit being represented by the presence or absence on an AML pulse~ ~s will be explained in urther detail hereinafter9 this 4-bit A~L control code is decoded by counting the number of ~ML pulses developed during each VBI and by determining the mode of operation of terminal 10 such that various two-way related functions of the terminal can be controlled from the headend.
With further reference to Figure 1, the AML pulses ~5 developed on line 36 by decoder 18 are cou~ed to a binary counter 22 and to a one-shot monostable multivibrator 24. Various other signals are also output by decoder 18 These signals include keystroke serial data provided via line 38 to a microcomputer 20. This keystroke serial data may inclu~e such inf~rmation as channel number selection, c~le selection, or program authorization requests as pro~ided ~o decoder ~8 via line 23 by a subscriber input device 21. This dat~ may also be provided directly from subscriber input device 21 to microcomputer 20 by means o~ line 55 eshown in dotted line form) in another embodiment. The decoder 18 is coupled to ground potential via line 40. Finally, decoder 18 provides a ~VDC output to the various components of the C~TV subscriber terminal 10 as required.
The AML pulses provided by decoder 18 to counter 22 lQ ~nd monostable multivib~ator 2~ are in the form of ~ microsecond pulses as shown in FIG. 2. ~s previousl~ mentioned, according to the present invention, various combinations of the AML pulses are ~ormed during each VBI by selectively transmitting appropriate address codes for selectively commanding each ~erminal from the headend. For example, the pulse diagram of FIG. 2 shows three AML pulses Pl, P2 and P3~ ~ML pulses Pl and P2 represent subscriber address code matches during VBI lines 10 and 11 while AML pulse P3 represents a market code match during VBI line 13. It will be appreciated that the market coda match AML pulse P3 cannot be used to represent any data since it is transmitted ~uring every VBI by the headend. During the subsequent field, an AML pulse P4 represents an address code match during VBI line 10 and an AM1 pulse P5 represents a market code match during VBI line 13. With each AML puls2 width equal to 8 microseconds~ a 64 microsecoDd interval is provided between adjacent AML p~s~s.
The ~ML pul ses produced on line 36 are providea to the A input of an OR gate 26, which in combination with multivibrator circuit 28 forms one-shot monostable multivibrator 24. The output of monostable multivibrator 24 is provided, in ~2~i;~
turn, to a D-type flip-flop circuit 30 which prov~es a timed output to ~ input p~ of ~icroc~mI)uter ~0 ~or initiating an interropt therein~ ~ollowing receipt from ~liF-flop 30 of an interrupt signal pr~vided to its I~T inp~lt pin, microcomputer 20, which in a preferred embodiment is an 8048 microcomputer with a 2K-ROM and a 64 byte RAM, finishes its current operation, or task, and executes another subroutine. In a preferred embodiment o~ the ~resent invention the ~ubroutine executed by mlc~ocomputer 20 following receipt of the interrup signal 1~ in~olve~ interprqting th~ headend command represen~d ~y the ~ML pulses developed during the current VBI and, if necessary the upstream transmission of data from the subscriber terminal 10 to the CATV headend 12 in response thereto. The upstream data transmission from microcomputer 20 is effected via output line 50, transmitter 16 and diplex filter 14.
In greater detail, the AML pulses on line 36 are provided to the A input of OR gate 26 o one-shot monostable multivibrator 24. The inverted 8 pin of OR gate 26 is coupled to a ~Vl sour~e. Each ~ML pulse provided to OR gate 26 triggers ~0 multivibrator 28 fQr initiating a negative-going pulse at its Q output which is coupled to the CLK input of D-type flip-flop circuit 30. The RC time constant of the circuit coupled to multivibrator 28 is selected such that the width of this negative-going pulse is about 250 ~icroseconds in a preferred embodiment. D-type flip-flop 30 is triggered by the positive going edge of the Q output of m~ltivibrator 2a. It will be recalled that an AML pulse is produced by decoder 18 during horizontal line 13 of each field in response to a market code match. The 250 microsecond duration of the output of monostable multivibrator 28 i5 of suffiojent length to insure triggering ~2B~
of flip-flop 30 on~y ~50 ~ic~oseconds after this marke~ code induced hori~ontal line 13 ~ML pulse so as to pro~id~ a precise timing reference signal at its Q output. In particular, multivi~rator 28 will be triggered or retriggered by the horizontal line 13 AML pulse regardless of the number of ~ML
pulses preceding it in a given field and before producing a positive-going output transition such that the Q output of ~lip-flop 30 will go low at a fixed time each field, i.e., 250 microseconds a~ter the hori~ontal line 13 AML pul~e.
la The low Q output f~om flip-~lop circuit 30 is provided ~o thR IN~ input pin of microcomputer 20 for initiating an illterrup routine ~or sampling the output of counter 22 provided on pins P21, P22 and P23 . Based on the sampled count and on the mode of the subscriber's terminal 10, appropriate responsive action is taken. Following a predetermined time interval a~
established by the operating program in the microcmputer's ROM
23 r microcomputer 20 provides a reset pulse from its P24 output pin to the RESET input o counter 22 and, via inverter 32, to the CLEA~ (C~) and RESET (~) inputs of multivibrator 28 and flip-flop 30, respectively. The reset output from microcomputer 20 prepares counter 22 and the combination of one-shot monostable multivibrator 24 and flip-flop 30 for receipt of the next series of AML pulses from decoder 18 during the VBI of a subsequent video field.
Counter 22 is a binary counter, to the CLK input of which is provided the AML pulses from decoder l~. ~ounter 22 provides a binary output signal vi~ lines 44, 46 and 48 to the P21 , P22 and P23 input pins~ respectively, of ~icr~computer 20 representing the number of AML pulses developed by decoder 18 during each field of the received signal. As will be explained in fu~ther detail below, acc~rding to the present invention this binary ~o~e~ si~n31 which, ~u~i~g each field, may take a value between dee~al l an~ decimal ~, is used to provide headend initiated command signals to microcomputer 2~ which may include syste~ status informati~n requests or headen~ initiated command signals for c~ntrolling each xe~ote subscriber terminal.
Referring to Table II, there is shown an exemplary definition of the headend commands represented by the multibit AML control siqnals which may be developed on line 36 during the VBI'S of the r~ceived signal and the corresponding output oE cQunter 2~. In this Table, a "l" represents the development oE an ~ML pulse in a particular VBI line by decoder 18 with the count of such AML pulses during each V~I by count~r 22 being given in decimal for~at. Also, for purposes of convenience the hori70ntal line 13 AML pulse is not considered since it is always present.
TABLE II
MODE 1 MODE 2 CO~NTER 22 MESSAGE PENDING STANDBY
VBI~DATA
LINES 10, 11, 12 (XXX ) (1~0) POSITIVE ACKNOWLEDGE (010) IGNORED
(0~1) (O 1 1 ) IGNORED (101) INTERROGATE 2 t~~
NBGATIVE ACKNOWLEDGE ~111) POWER ADJUSTMENT 3 MPL : MESSAGB PENDING LIGHT (YELLOW LED~
EPL : ERROR LIGHT (RED LED) ACL : ACKNOWLEDGE LIGHT (GREEN LED) ~æo~7 ~ n accordance with the p~esent inventio~, each subscriber terminal 10 is capable of operating in two different modes. a first mode is termed the "message pending" mode, while the second mode of operation is termed "standby". In the message pending mode, the subscri~er terminal 10 has transmitted a message upstream to the CATV headend 12, such as a program authori~ation request, and is waiting for a response thereto ~om the headend. The upstream message may be generated in r~pon~ to ~uhscriber en~rias via subscriber input device 21 which, in turn, are provided to microcomputer 20. The headend response may be in the form of a POSITIVE ACKNOWLEDGE command (indicating that the requested program authorization will be granted) or a NEGATIV~ ACKNOWLEDGE command (indicating that the reguested program authorization will not be granted).
In a second standby mode of operation the subscriber terminal 10 is in a ready state for receipt of downstream data from the CATV headend~ In this mode, receipt of downstream data by the subscriber terminal 10 results in the performance of a specific operation by the subscriber terminal or the providing of information from subscriber terminal 10 to the CATV headend 12.
From TABLE II, it can be seen that the subscriber terminal interp~et~ downstream data from the C~TV headend 12 in accordance with its operating mode. For example, a signle AML pulse in any of VBI lines 10, 11 or 12 (represented by counter 22 accumulating a "1" count during the complete VBI) represents a POSITEVE ACKNOWLEDGE signal from the CATV headend when the subscriber terminal is in the message pending mode of pending mode of operation and i5 ignored when the terminal is in the sandby mode of operation~ Tw~ AML pulses received in any of ~ I lines ~r 11 and 12 (represented by counter 22 accumulating a "2'` count during the VBI~ is interpreted by the 5 terminal when in the standby mode as an INTERROG~TE command and is ignored in the message pending mode. Finally, an AML pulse received in each of VBI lines 10, 11 and 12 ~represented by counter 22 accumulating a "3" count during the VBI) represents a NEGA~I~E AcKNowLEaGE command from the CArV headend 12 to 1~ sub~c~ib~r ~erminal 10 in the message pending mode ancl as a POWER
~JUSTMEN~ comm~nd in the standby mode.
As mentioned previously the POSITIVE or NEGA'rIVE
ACKNOWLEDGE commands may be used by the headend to provide an answer or response to a program authorization request by a subscriber. For example, receipt of a POSITIVE ACKNOWLEDGE
command by a subscriber terminal may indicate that an upstream request for access to a CATV program is acknowledged and that decode authorization for the req~ested program will be granted by the CATV headend. On the other hand, a NEG~TIVE ACKNOWLEDGE
may indicate that the request has been denied. The INTERROGATE
command may, for example, represent a request by the CATV headend for the subscriber terminal to provide information relating to the channel to which the subscriber terminal is tuned. Various other subscriber ~erminal operating parameters may be requested by means of the INTERRO~ATE command ignal from the CATV headend.
With t~e CATV terminal in the standby mode, receipt of an AML pulse in each of VBI lines lO, 11 and 12 (represented by the accumulation of a "3" count by counter 22 during the VBI~
represents a POWER ADJUSTMENT command for adjusting the upstream signal power output of the subscriber terminal. The direction ~209~
of power a~ t~ent ~y the subscriber terminal is determined by the state of ~ e~ ~emory 35 within the random access memory lR~ 25 of mi~rocomputer 20. The power memory 35 in a preferred embodiment is ~ power s~at1~s memory bit within the S microcomputer's RA~ 25. The power memory 35 operates as a binary switch which changes its state in response to receipt of an INTERROG~TE command from the CATV headend 12 when the subscriber terminal ~0 is in the standby mode of operation. Each time the sub~criber terminal 10 receives an INTE~ROGATE command from the ln CA~V headend, the power memory 35 changes state. In addition, r~pon~e is provided by the subscriber terminal 10 to the CATV
h~ad~nd 12 indicat~ng whether power will be increased or decreased following receipt of the next POWE~ ADJUSTMENT signal from the CATV headend. Thus, after the CATV headend determines whether the subscriber terminal power is to be increased or decreased and using the aforementioned power memory status information/ the CATV headend then decides whether its next output should be an INTERROGATE command or a POWER ADJUSTMENT
command. If the power memory 35 is set in the desired direction, ~ the CATV headend will next provide a POWER ADJUSTMENT command to the subscriber terminal~ If, however, the CATV headend determines that a power adjustment exe~ut~ by the subscriber terminal will be in the wrong direction, it provides an INTERROGATE command to the subscriber terminal which changes the ~tate of ~he power memory 35 to permit subscriber terminal power to be adiusted in the opposite direction following receipt of the next POWER A~JUSTM~NT comman~ from ~he CAI'V headend.
The INTERROGATE c~m~aDd ~hus ~cts to toggle the power memory 35 and results in a response from the subscriber terminal 10 to the CATV headend 12 with a status message. The POWER
~209e~7 ~DJUSTMEN~ com~nan~ 5es eit~er an increm~nting or a decrementing of th~ subscriber *ermi~l output power and also results in a power signal being provided fr~m the subscriber terminal-lO to the CATV headend 12~
In c~njunction with the various commands provided from the CATV headend to a subscriber terminal, visual indications may be provided to a subscriber for indicating system status.
F4r e~ample, various light emitting diodes ~LED's) 60, 62 and 64 may b~ coupled ~o the microcomp~er 20 b~ means oF plu~allty l~ o r~ driv~xs 66 ~o~ providing a visual indication o ~he c~mmand or status signal received from the C~TV headend 12.
For example, in a preferred embodiment LED 60 (MPL) is a Message Pending Light used to indicate that a subscriber initiated message is pending, that the CATV headend 12 is currently busy executing another task, and that a response to the subscriber's request will be provided after the current task has been per~ormed. LED 62 tERL) is used to indicate the antry hy a subs~riber of an incorrect password or that the subscriber is not eliqible for the program requested (i.e. a NEGATIVE
~O ACKNOWLEDGE command). F;nally, illumination of LED 64 (ACL) indicates to the subscIiber an acknowledgement of receipt by CATV headend 12 of its upstream message and that the subscriber's request has been authorized (i.e. a POSITIVE ACKNOWLEDGE
command)~These LED' s are of different colors to factilitate visual identification of these various status and command signals by the subscriber. For example, the Message Pending Light 60 may by yellow, t-h- Err~ Light 62 may be red, and the Acknowledge Light 64 may be green.
There has thus been shown a two-way C~TV system wherein headend initiated commands are transmitted durin~ the vertical . ~os~7 blanking interval of the downstream video program signals along with subscriber address an~ ~ro~ram au~ori2ation data. The command ~ignal~ are in the orm D a m~ ibit code, each bit of which ~s ~epresented by the transmission or non-transmission S of a subscriber addr~s~ ~de. Each ~ansmitted address code is compared to an ~ddress code stored in the subscriber terminal or generating the multibit command code, the bits o which are subse~uently counted for decoding in accordance with ~he mode of operation of the terminal so as to control a selected function the~eo~
While particular embodiments of the pre~ent invention hav~ been shown and described, it will be obvious to tho~e skilled in the art that changes and modification may be made without departing from the invention in its broader aspects.
Therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and ~cope of invention. The matter set forth in the foregoing description and accompanying drawings is offered by way of illusteation only and not as a limitation. The actual scope ~ o the invention is intended to be defined in the following claims when viewed in their proper perspective based on the prior art.
Background o~ the Invention _ _ _ This invention relates generally ~o two-way cable television (CATV) systems and is particularly directed to the transmission of data ~rom the headend to a plurality o~
s~bscribers in a two-way CATV system.
C~TV systems typically include a central master source of television programming in~ormation termed a headend which imparts programs, or groups o~ programs at different assigned ~requencies, to a network o~ cable connections which, through varlous distributian and selection network components, ultimately t~rmin~t~ in ~ branched out plurality o subscriber terminals typi~lly in residen'ce or commercial establishments. CATV
program signals are broadcast ~rom the headend to individual subscribers in a `'downstream" direction over different assigned carrier req~encies typicall~ from ~bout 50 to 450 MHz~ The CATV headend not only ~ransmits television programming informa'iol. downst~eam, but may also transmit data in the orm Q~ for example, subscriber address and authorization inormation, which allows ~he stored program de~ode authorization status of each subscriber to ~e individually controlled from the headend. Frequently, such data is encoded in the vertical 12~
blanking interval ~BI) of a transmitted CATV program signal.
The program d~c~d~ a~t~riz3ti~D ~tatus st~red in each subscrib~r' s ~erminal is co~pared with a program code also encoded in the VBI of the received CATV signal to establish whether ~r not the subscri~er is authorized for decoding the r ece i ved prog r am s ig na 1 .
In a two-way C~V system each subscriber i5 able to transmit signals back to the CA~V headend. These ~ub~crib~r-originated ~ignals may in~lude program purchasing r~u~t~, opinion poll re~ponses, and C~TV conver~er status information. ~hese upstream signals typically make use of out of band fre~uencies in the 5-32.5 MHz band. The upstream signal distribution network is in the form of a "merging tree topology"
in which the signals generated by many sources, or subscribers, converge and are transmitted on a single transmission line back to the CATV headend. Such techniques as signal multiplexing and re~ency diversity have been proposed and are utilized to accomodate large numbers of subscribers in two-way CATV systems~
Proper response to the subscriber-originated signals normally re~uires the exercise of headend control over the various remotely located subscriber terminals coupled to the CATV system. The exercise of such control requires the downstream transmission of various command signals from the headend controller to t~e su~scriber terminals.
The present invention provides a facility whereby such headend control of subscriber terminals may be conventiently realized within the environment of a prior art C~TV system employing VBI data transmission techniques. In particular, a headend command signal is transmitted during a single VBI in the form of a multibit code, each bit of which is represented ~9~
by the transmission or non-transm;ssio~ of a subscriber address code during a respective pr~deter~ined time interval of the VBI.
At the subscriber's terminal, the received address codes are processed to reconstruct the multibit code which is subsequently decoded ~or use in controlling various aspects of the terminal.
~ects o the Invention -Accordingly, it is a ba~ic object of the present invention to provide a facility for enabling headend control of a plurality of subscriber terminals in a two-way C~TV system.
It 15 a more specific object o~ the present invention to provide such a facility in the environment of an addressable CA~V ~ystem using VBI data transmission techniques.
Yet another object of the present invention is to provide such a facility in an extremely convenient and cost-ef~ective manner.
Brief Desc_ ~ion of the Drawings The appended claims set forth those novel features believed characteristic of the invention. However, the invention itsel, as well as further objects and advantages thereof, will best be understood by reference to the following detailed description of the preferred embodiment taken in conjunction with the accompanying drawings, in which:
FIG. 1 shows in block and schematic diagram form a two-way CATV system in accordance with the present invention; and ~5 FIG. 2 is a waveform diagrarn useful in explaining the operation of the system s~own in Figure 1.
Descri~tion of the Preferred Embc~imen~
~ ferring to FIG. 1, there is shown in combined schematic and block diagram form a subscriber terminal 10 for a two-way CATV system in accordance with the present invention.
12~
The system also includes a cable headend 12 coupled to each subscriber t~in~l ~O via a cable 15 and which typically includes a co~puter mu3ti~le terminals, disc drives an~ a tape backup. -These el2men~s of the ca~le headend 12 are not shown in FIG. l as they do not form a par~ of the present invention.
Downstream signals from the cable headend ~2 to indlvidual subscribers may include such infor~ation as subscriber address, program auth~rization, and market codes as well as program identifiGatlon data which is transmitted in televlsion channels h~vin~ F~uencies between abo~t S0 and 450 MHz. This data may b~ provld~d during the vertical blanking interval (VBI) o the down~ream video program~ing signals, such as in lines 10 through 13 of the V~I as shown in Table I. Although the present invention is described herein as making use of VBI lines 10-13 lS o the video programming signals for the downstream transmission of subscriber terminal commands, it is not limited to the use of these VBI lines and may utilize any portion of the vertical retrace signal including any combination of VBI lines, consecutive or nonconsecutive.
_ _ _ _ _ ._ __ _ _ . _ _ _ __ _ n-BIT
V~I Line 1~ m-BIT ADDRESS CODE AUTHORIZATION CODE
n-BIT
VBI Line 11 m-BIT ADDRESS CODE AUTHORIZ~TION CODE
n-BIT
VBI Line 1~ m-BlT hDDRESS CODE ~UTHORIZATIO~ CODE
_ _ __ _ _____ __ _ _ _ ___ __ __ VBI Line 13 x-BIT MARKET CODE y-BI~ PROGRAM TAG
The VBI occ~rs during vertical retrace o~ the raster scanned cathode ray tube ICRT~ of t~e subscriber's television receiver and co~prises ~hout 21 horizontal scanning lines.
~20~6~5P7 Referring to Table I above, in a known one-way addressable CATV
system a~ ~ bit subscriber add~e~ de an~ a related n-bit program a~ ri-z~ti~ de a~? selectively transmitted during each of lines 10~ 11 and 12 of the ~ ach address code may comprise 2~ s with each authorization code comprising 5 bits.
During line 13 of the VBI there is continuously transmitted an x-bit (e~g.ll bits) market code which defines the geographic area in which the system is operating as well as a y-bit (e.g~ 7 bits) progra-~ identification ~ode, or tag, defining the 1~ a~companying televlsion program. These downstream ~ nals ~re received by each subscriber terminal 10 and coupled by a diplex filter 14 to a decoder 18 which includes a suitable tuner tuned to an encoded CATV channel. Each received m-bit address code is compared with a unique subscriber address code stored in a programmable read only memory (PROM) 34 of decoder 18 in each subscriber terminal 10. If the received subscriber address code matches the unique~subscriber address code stored in the decoder's PROM 34, the program authori7ation code o~ the same VB I line is stored in a random access memory ~RAM) 78 in decoder 18 which defines the program decode authorization status of the subscriber. A match between the received and stored address codes will also result in the generation of an address match latch (AML) pulse by decoder 18, which pulse is provided on an output line 36 of decoder 18.
The x-bit market code received during line 13 of each VBI is compared with a subscriber terminal market code also stored in the decode~'s PROM 34. A match between the transmitted and stored market codes will enable the decoder 18 an~ also result in the gener~tion of an address match latch ~AML) pulse which is similarly provided on line 3~. A match between the ~2~
received y bit program tag ~ode and thi~ ~tored program decode au~hroization status permits the decode~ to descra~ble the received CATV video programming signal ~hich may then be viewed on the sub~criber'~ ~le~ision receiver (not shown~. The absence 5 of a match between the received program tag code and the stored program authorization status results in the video programming signal being passed on by the subscriber terminal 10 in a scrambled form. Theraafter, decoder 18 cont;nuously monitors incoming data for detecting each subsequent address or market ln cod~ match.
.~s previously mentionQA, each match between a recQived ~ubscriber address code and the unique subscriber address code stored in PROM 34 of decoder 18 results in an AML pulse on line 36. ~ccording to the present invention, the selective transmission of subscriber address codes on horizontal lines 10-13 of the VBI is used to provide a 4-bit headend command control code on line 36, each bit being represented by the presence or absence on an AML pulse~ ~s will be explained in urther detail hereinafter9 this 4-bit A~L control code is decoded by counting the number of ~ML pulses developed during each VBI and by determining the mode of operation of terminal 10 such that various two-way related functions of the terminal can be controlled from the headend.
With further reference to Figure 1, the AML pulses ~5 developed on line 36 by decoder 18 are cou~ed to a binary counter 22 and to a one-shot monostable multivibrator 24. Various other signals are also output by decoder 18 These signals include keystroke serial data provided via line 38 to a microcomputer 20. This keystroke serial data may inclu~e such inf~rmation as channel number selection, c~le selection, or program authorization requests as pro~ided ~o decoder ~8 via line 23 by a subscriber input device 21. This dat~ may also be provided directly from subscriber input device 21 to microcomputer 20 by means o~ line 55 eshown in dotted line form) in another embodiment. The decoder 18 is coupled to ground potential via line 40. Finally, decoder 18 provides a ~VDC output to the various components of the C~TV subscriber terminal 10 as required.
The AML pulses provided by decoder 18 to counter 22 lQ ~nd monostable multivib~ator 2~ are in the form of ~ microsecond pulses as shown in FIG. 2. ~s previousl~ mentioned, according to the present invention, various combinations of the AML pulses are ~ormed during each VBI by selectively transmitting appropriate address codes for selectively commanding each ~erminal from the headend. For example, the pulse diagram of FIG. 2 shows three AML pulses Pl, P2 and P3~ ~ML pulses Pl and P2 represent subscriber address code matches during VBI lines 10 and 11 while AML pulse P3 represents a market code match during VBI line 13. It will be appreciated that the market coda match AML pulse P3 cannot be used to represent any data since it is transmitted ~uring every VBI by the headend. During the subsequent field, an AML pulse P4 represents an address code match during VBI line 10 and an AM1 pulse P5 represents a market code match during VBI line 13. With each AML puls2 width equal to 8 microseconds~ a 64 microsecoDd interval is provided between adjacent AML p~s~s.
The ~ML pul ses produced on line 36 are providea to the A input of an OR gate 26, which in combination with multivibrator circuit 28 forms one-shot monostable multivibrator 24. The output of monostable multivibrator 24 is provided, in ~2~i;~
turn, to a D-type flip-flop circuit 30 which prov~es a timed output to ~ input p~ of ~icroc~mI)uter ~0 ~or initiating an interropt therein~ ~ollowing receipt from ~liF-flop 30 of an interrupt signal pr~vided to its I~T inp~lt pin, microcomputer 20, which in a preferred embodiment is an 8048 microcomputer with a 2K-ROM and a 64 byte RAM, finishes its current operation, or task, and executes another subroutine. In a preferred embodiment o~ the ~resent invention the ~ubroutine executed by mlc~ocomputer 20 following receipt of the interrup signal 1~ in~olve~ interprqting th~ headend command represen~d ~y the ~ML pulses developed during the current VBI and, if necessary the upstream transmission of data from the subscriber terminal 10 to the CATV headend 12 in response thereto. The upstream data transmission from microcomputer 20 is effected via output line 50, transmitter 16 and diplex filter 14.
In greater detail, the AML pulses on line 36 are provided to the A input of OR gate 26 o one-shot monostable multivibrator 24. The inverted 8 pin of OR gate 26 is coupled to a ~Vl sour~e. Each ~ML pulse provided to OR gate 26 triggers ~0 multivibrator 28 fQr initiating a negative-going pulse at its Q output which is coupled to the CLK input of D-type flip-flop circuit 30. The RC time constant of the circuit coupled to multivibrator 28 is selected such that the width of this negative-going pulse is about 250 ~icroseconds in a preferred embodiment. D-type flip-flop 30 is triggered by the positive going edge of the Q output of m~ltivibrator 2a. It will be recalled that an AML pulse is produced by decoder 18 during horizontal line 13 of each field in response to a market code match. The 250 microsecond duration of the output of monostable multivibrator 28 i5 of suffiojent length to insure triggering ~2B~
of flip-flop 30 on~y ~50 ~ic~oseconds after this marke~ code induced hori~ontal line 13 ~ML pulse so as to pro~id~ a precise timing reference signal at its Q output. In particular, multivi~rator 28 will be triggered or retriggered by the horizontal line 13 AML pulse regardless of the number of ~ML
pulses preceding it in a given field and before producing a positive-going output transition such that the Q output of ~lip-flop 30 will go low at a fixed time each field, i.e., 250 microseconds a~ter the hori~ontal line 13 AML pul~e.
la The low Q output f~om flip-~lop circuit 30 is provided ~o thR IN~ input pin of microcomputer 20 for initiating an illterrup routine ~or sampling the output of counter 22 provided on pins P21, P22 and P23 . Based on the sampled count and on the mode of the subscriber's terminal 10, appropriate responsive action is taken. Following a predetermined time interval a~
established by the operating program in the microcmputer's ROM
23 r microcomputer 20 provides a reset pulse from its P24 output pin to the RESET input o counter 22 and, via inverter 32, to the CLEA~ (C~) and RESET (~) inputs of multivibrator 28 and flip-flop 30, respectively. The reset output from microcomputer 20 prepares counter 22 and the combination of one-shot monostable multivibrator 24 and flip-flop 30 for receipt of the next series of AML pulses from decoder 18 during the VBI of a subsequent video field.
Counter 22 is a binary counter, to the CLK input of which is provided the AML pulses from decoder l~. ~ounter 22 provides a binary output signal vi~ lines 44, 46 and 48 to the P21 , P22 and P23 input pins~ respectively, of ~icr~computer 20 representing the number of AML pulses developed by decoder 18 during each field of the received signal. As will be explained in fu~ther detail below, acc~rding to the present invention this binary ~o~e~ si~n31 which, ~u~i~g each field, may take a value between dee~al l an~ decimal ~, is used to provide headend initiated command signals to microcomputer 2~ which may include syste~ status informati~n requests or headen~ initiated command signals for c~ntrolling each xe~ote subscriber terminal.
Referring to Table II, there is shown an exemplary definition of the headend commands represented by the multibit AML control siqnals which may be developed on line 36 during the VBI'S of the r~ceived signal and the corresponding output oE cQunter 2~. In this Table, a "l" represents the development oE an ~ML pulse in a particular VBI line by decoder 18 with the count of such AML pulses during each V~I by count~r 22 being given in decimal for~at. Also, for purposes of convenience the hori70ntal line 13 AML pulse is not considered since it is always present.
TABLE II
MODE 1 MODE 2 CO~NTER 22 MESSAGE PENDING STANDBY
VBI~DATA
LINES 10, 11, 12 (XXX ) (1~0) POSITIVE ACKNOWLEDGE (010) IGNORED
(0~1) (O 1 1 ) IGNORED (101) INTERROGATE 2 t~~
NBGATIVE ACKNOWLEDGE ~111) POWER ADJUSTMENT 3 MPL : MESSAGB PENDING LIGHT (YELLOW LED~
EPL : ERROR LIGHT (RED LED) ACL : ACKNOWLEDGE LIGHT (GREEN LED) ~æo~7 ~ n accordance with the p~esent inventio~, each subscriber terminal 10 is capable of operating in two different modes. a first mode is termed the "message pending" mode, while the second mode of operation is termed "standby". In the message pending mode, the subscri~er terminal 10 has transmitted a message upstream to the CATV headend 12, such as a program authori~ation request, and is waiting for a response thereto ~om the headend. The upstream message may be generated in r~pon~ to ~uhscriber en~rias via subscriber input device 21 which, in turn, are provided to microcomputer 20. The headend response may be in the form of a POSITIVE ACKNOWLEDGE command (indicating that the requested program authorization will be granted) or a NEGATIV~ ACKNOWLEDGE command (indicating that the reguested program authorization will not be granted).
In a second standby mode of operation the subscriber terminal 10 is in a ready state for receipt of downstream data from the CATV headend~ In this mode, receipt of downstream data by the subscriber terminal 10 results in the performance of a specific operation by the subscriber terminal or the providing of information from subscriber terminal 10 to the CATV headend 12.
From TABLE II, it can be seen that the subscriber terminal interp~et~ downstream data from the C~TV headend 12 in accordance with its operating mode. For example, a signle AML pulse in any of VBI lines 10, 11 or 12 (represented by counter 22 accumulating a "1" count during the complete VBI) represents a POSITEVE ACKNOWLEDGE signal from the CATV headend when the subscriber terminal is in the message pending mode of pending mode of operation and i5 ignored when the terminal is in the sandby mode of operation~ Tw~ AML pulses received in any of ~ I lines ~r 11 and 12 (represented by counter 22 accumulating a "2'` count during the VBI~ is interpreted by the 5 terminal when in the standby mode as an INTERROG~TE command and is ignored in the message pending mode. Finally, an AML pulse received in each of VBI lines 10, 11 and 12 ~represented by counter 22 accumulating a "3" count during the VBI) represents a NEGA~I~E AcKNowLEaGE command from the CArV headend 12 to 1~ sub~c~ib~r ~erminal 10 in the message pending mode ancl as a POWER
~JUSTMEN~ comm~nd in the standby mode.
As mentioned previously the POSITIVE or NEGA'rIVE
ACKNOWLEDGE commands may be used by the headend to provide an answer or response to a program authorization request by a subscriber. For example, receipt of a POSITIVE ACKNOWLEDGE
command by a subscriber terminal may indicate that an upstream request for access to a CATV program is acknowledged and that decode authorization for the req~ested program will be granted by the CATV headend. On the other hand, a NEG~TIVE ACKNOWLEDGE
may indicate that the request has been denied. The INTERROGATE
command may, for example, represent a request by the CATV headend for the subscriber terminal to provide information relating to the channel to which the subscriber terminal is tuned. Various other subscriber ~erminal operating parameters may be requested by means of the INTERRO~ATE command ignal from the CATV headend.
With t~e CATV terminal in the standby mode, receipt of an AML pulse in each of VBI lines lO, 11 and 12 (represented by the accumulation of a "3" count by counter 22 during the VBI~
represents a POWER ADJUSTMENT command for adjusting the upstream signal power output of the subscriber terminal. The direction ~209~
of power a~ t~ent ~y the subscriber terminal is determined by the state of ~ e~ ~emory 35 within the random access memory lR~ 25 of mi~rocomputer 20. The power memory 35 in a preferred embodiment is ~ power s~at1~s memory bit within the S microcomputer's RA~ 25. The power memory 35 operates as a binary switch which changes its state in response to receipt of an INTERROG~TE command from the CATV headend 12 when the subscriber terminal ~0 is in the standby mode of operation. Each time the sub~criber terminal 10 receives an INTE~ROGATE command from the ln CA~V headend, the power memory 35 changes state. In addition, r~pon~e is provided by the subscriber terminal 10 to the CATV
h~ad~nd 12 indicat~ng whether power will be increased or decreased following receipt of the next POWE~ ADJUSTMENT signal from the CATV headend. Thus, after the CATV headend determines whether the subscriber terminal power is to be increased or decreased and using the aforementioned power memory status information/ the CATV headend then decides whether its next output should be an INTERROGATE command or a POWER ADJUSTMENT
command. If the power memory 35 is set in the desired direction, ~ the CATV headend will next provide a POWER ADJUSTMENT command to the subscriber terminal~ If, however, the CATV headend determines that a power adjustment exe~ut~ by the subscriber terminal will be in the wrong direction, it provides an INTERROGATE command to the subscriber terminal which changes the ~tate of ~he power memory 35 to permit subscriber terminal power to be adiusted in the opposite direction following receipt of the next POWER A~JUSTM~NT comman~ from ~he CAI'V headend.
The INTERROGATE c~m~aDd ~hus ~cts to toggle the power memory 35 and results in a response from the subscriber terminal 10 to the CATV headend 12 with a status message. The POWER
~209e~7 ~DJUSTMEN~ com~nan~ 5es eit~er an increm~nting or a decrementing of th~ subscriber *ermi~l output power and also results in a power signal being provided fr~m the subscriber terminal-lO to the CATV headend 12~
In c~njunction with the various commands provided from the CATV headend to a subscriber terminal, visual indications may be provided to a subscriber for indicating system status.
F4r e~ample, various light emitting diodes ~LED's) 60, 62 and 64 may b~ coupled ~o the microcomp~er 20 b~ means oF plu~allty l~ o r~ driv~xs 66 ~o~ providing a visual indication o ~he c~mmand or status signal received from the C~TV headend 12.
For example, in a preferred embodiment LED 60 (MPL) is a Message Pending Light used to indicate that a subscriber initiated message is pending, that the CATV headend 12 is currently busy executing another task, and that a response to the subscriber's request will be provided after the current task has been per~ormed. LED 62 tERL) is used to indicate the antry hy a subs~riber of an incorrect password or that the subscriber is not eliqible for the program requested (i.e. a NEGATIVE
~O ACKNOWLEDGE command). F;nally, illumination of LED 64 (ACL) indicates to the subscIiber an acknowledgement of receipt by CATV headend 12 of its upstream message and that the subscriber's request has been authorized (i.e. a POSITIVE ACKNOWLEDGE
command)~These LED' s are of different colors to factilitate visual identification of these various status and command signals by the subscriber. For example, the Message Pending Light 60 may by yellow, t-h- Err~ Light 62 may be red, and the Acknowledge Light 64 may be green.
There has thus been shown a two-way C~TV system wherein headend initiated commands are transmitted durin~ the vertical . ~os~7 blanking interval of the downstream video program signals along with subscriber address an~ ~ro~ram au~ori2ation data. The command ~ignal~ are in the orm D a m~ ibit code, each bit of which ~s ~epresented by the transmission or non-transmission S of a subscriber addr~s~ ~de. Each ~ansmitted address code is compared to an ~ddress code stored in the subscriber terminal or generating the multibit command code, the bits o which are subse~uently counted for decoding in accordance with ~he mode of operation of the terminal so as to control a selected function the~eo~
While particular embodiments of the pre~ent invention hav~ been shown and described, it will be obvious to tho~e skilled in the art that changes and modification may be made without departing from the invention in its broader aspects.
Therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and ~cope of invention. The matter set forth in the foregoing description and accompanying drawings is offered by way of illusteation only and not as a limitation. The actual scope ~ o the invention is intended to be defined in the following claims when viewed in their proper perspective based on the prior art.
Claims (8)
1. In a two-way CATV system wherein video program signals are transmitted downstream from a headend to a plurality of subscriber terminals each uniquely identified by a respective stored multibit subscriber address code and wherein a plurality of multibit subscriber address codes may be selectively transmitted during a vertical blanking interval of said video program signals, a system for controlling a selected subscriber terminal from said headend comprising:
means associated with said headend for transmitting multibit command code during the VBI of a selected field of said program signal for controlling said selected subscriber terminal, each bit of said command code being represented by a transmission or non-transmission during a respective time interval of the address code corresponding to the stored address code identifying said selected subscriber terminal;
means coupled to said cable for receiving the transmitted command code and for generating a match signal in response to each received address code that corresponds to the stored address code identifying said selected subscriber terminal; and means for decoding the match signals generated during each vertical blanking interval for selectively controlling said selected subscriber terminal.
means associated with said headend for transmitting multibit command code during the VBI of a selected field of said program signal for controlling said selected subscriber terminal, each bit of said command code being represented by a transmission or non-transmission during a respective time interval of the address code corresponding to the stored address code identifying said selected subscriber terminal;
means coupled to said cable for receiving the transmitted command code and for generating a match signal in response to each received address code that corresponds to the stored address code identifying said selected subscriber terminal; and means for decoding the match signals generated during each vertical blanking interval for selectively controlling said selected subscriber terminal.
2. A subscriber terminal control system as in claim 1 wherein each of said multibit address codes is transmitted on a different horizontal line of the vertical blanking interval of said selected field.
3. A subscriber terminal control system as in claim 2 wherein said decoding means comprises means for counting the number of said match signal developed during the vertical blanking interval of said selected field.
4. A subscriber terminal control system as in claim 3 wherein said subscriber terminal is operable in a first STANDBY
mode wherein said subscriber terminal awaits receipt of a headend-initiated command code or, in response to subscriber inputs, is operable in a second MESSAGE PENDING mode wherein said subscriber terminal awaits acknowledgment for the headend of receipt of an upstream message from said subscriber terminal and wherein said decoding means comprises means responsive to the number of said match signals counted during the vertical blanking interval of said selected field and to the mode of operation of said subscriber terminal for decoding said transmitted command code.
mode wherein said subscriber terminal awaits receipt of a headend-initiated command code or, in response to subscriber inputs, is operable in a second MESSAGE PENDING mode wherein said subscriber terminal awaits acknowledgment for the headend of receipt of an upstream message from said subscriber terminal and wherein said decoding means comprises means responsive to the number of said match signals counted during the vertical blanking interval of said selected field and to the mode of operation of said subscriber terminal for decoding said transmitted command code.
5. A subscriber terminal control system as in claim 4 including means for providing an observable indication to the subscriber of the mode of operation of the subscriber terminal and of the receipt by the terminal of selected headend command codes.
6. A subscriber terminal control system as in claim 4 wherein said subscriber terminal includes a power direction memory whose state in toggled in response to the receipt of a first predetermined headend command code when the terminal is in the standby mode and further including means for adjusting the upstream power transmission level of the terminal in accordance with the state of the power direction memory in response to the receipt of a second predetermined headend command code when the terminal is in the standby mode.
7. In a two-way CATV system wherein video program signals are transmitted downstream from a headend to a plurality of subscriber terminals each uniquely identified by a respective stored multibit subscriber address code and wherein a plurality of multibit subscriber codes may be selectively transmitted during respective lines of a vertical blanking interval of said video program signals, a system for controlling a selected subscriber terminal from said headend comprising:
means associated with said headend for transmitting a multibit command code during the VBI of a selected field of said program signal for controlling said selected subscriber terminal, each bit of said command code being represented by the transmission or non-transmission during a respective vertical interval line of the address code corresponding to the stored address code identifying said selected subscriber terminal;
means coupled to said cable for receiving the transmitted command code and for generating a match signal in response to each received address code that corresponds to the stored address code identifying said selected subscriber terminal; and decoding means for counting the match signals generated during each vertical blanking interval for selectively controlling said selected subscriber terminal in accordance with the number of match signals counted.
means associated with said headend for transmitting a multibit command code during the VBI of a selected field of said program signal for controlling said selected subscriber terminal, each bit of said command code being represented by the transmission or non-transmission during a respective vertical interval line of the address code corresponding to the stored address code identifying said selected subscriber terminal;
means coupled to said cable for receiving the transmitted command code and for generating a match signal in response to each received address code that corresponds to the stored address code identifying said selected subscriber terminal; and decoding means for counting the match signals generated during each vertical blanking interval for selectively controlling said selected subscriber terminal in accordance with the number of match signals counted.
8. In a two-way CATV system wherein video program signals are transmitted downstream from a headend to a plurality of subscriber terminals each uniquely identified by a respective stored multibit subscriber address code and wherein a plurality of multibit subscriber address codes may be selectively transmitted during a vertical blanking interval of said video program signals, a system for controlling a selected subscriber terminal from said headend comprising:
means associated with said headend for transmitting a multibit command code during the VBI of a selected field of said program signal for controlling said selected subscriber terminal, each bit of said command code being represented by the transmission or non-transmission during a respective time interval of the address code corresponding to the stored address code identifying said selected subscriber terminal;
means coupled to said cable for receiving the transmitted command code and for generating a match signal in response to each received address code that corresponds to the stored address code identifying said selected subscriber terminal;
means for decoding the match signals generated during each vertical blanking interval; and a power direction memory whose state is toggled in response to a first predetermined decoded headend command code and further including means for incrementally adjusting the upstream power transmission level of the terminal in accordance with the state of the power direction memory in response to a second predetermined decoded headend command.
means associated with said headend for transmitting a multibit command code during the VBI of a selected field of said program signal for controlling said selected subscriber terminal, each bit of said command code being represented by the transmission or non-transmission during a respective time interval of the address code corresponding to the stored address code identifying said selected subscriber terminal;
means coupled to said cable for receiving the transmitted command code and for generating a match signal in response to each received address code that corresponds to the stored address code identifying said selected subscriber terminal;
means for decoding the match signals generated during each vertical blanking interval; and a power direction memory whose state is toggled in response to a first predetermined decoded headend command code and further including means for incrementally adjusting the upstream power transmission level of the terminal in accordance with the state of the power direction memory in response to a second predetermined decoded headend command.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US56002983A | 1983-12-09 | 1983-12-09 | |
| US560,029 | 1983-12-09 | ||
| US06/648,841 US4554579A (en) | 1983-12-09 | 1984-09-06 | Two-way CATV system with AML commands |
| US648,841 | 1984-09-06 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1209687A true CA1209687A (en) | 1986-08-12 |
Family
ID=27072233
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000469597A Expired CA1209687A (en) | 1983-12-09 | 1984-12-07 | Two-way catv system with aml commands |
Country Status (4)
| Country | Link |
|---|---|
| US (1) | US4554579A (en) |
| EP (1) | EP0163734A1 (en) |
| CA (1) | CA1209687A (en) |
| WO (1) | WO1985002743A1 (en) |
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|---|---|---|---|---|
| US3769579A (en) * | 1972-03-31 | 1973-10-30 | Oak Electro Netics Corp | Cable television monitoring system |
| US3750022A (en) * | 1972-04-26 | 1973-07-31 | Hughes Aircraft Co | System for minimizing upstream noise in a subscriber response cable television system |
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| US4107734A (en) * | 1977-01-31 | 1978-08-15 | R. D. Percy & Company | Television viewer reaction determining system |
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| JPS56169480A (en) * | 1980-05-30 | 1981-12-26 | Pioneer Electronic Corp | Inspection signal generating device in catv system |
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| US4460922A (en) * | 1981-11-18 | 1984-07-17 | Zenith Electronics Corporation | Memory select system for an STV decoder |
| FR2524242B1 (en) * | 1982-03-24 | 1986-02-07 | Radiotechnique | ENCRYPTION RECOGNITION CIRCUIT FOR TELEVISION BROADCASTING TRANSMISSION SYSTEM AND ENCRYPTED BROADCASTING TRANSMISSION SYSTEM INCLUDING SUCH A CIRCUIT |
| US4512033A (en) * | 1982-11-29 | 1985-04-16 | C-Cor Labs, Inc. | Remote level adjustment system for use in a multi-terminal communications system |
-
1984
- 1984-09-06 US US06/648,841 patent/US4554579A/en not_active Expired - Lifetime
- 1984-12-07 WO PCT/US1984/001996 patent/WO1985002743A1/en unknown
- 1984-12-07 CA CA000469597A patent/CA1209687A/en not_active Expired
- 1984-12-07 EP EP85900376A patent/EP0163734A1/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| US4554579A (en) | 1985-11-19 |
| EP0163734A1 (en) | 1985-12-11 |
| WO1985002743A1 (en) | 1985-06-20 |
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Legal Events
| Date | Code | Title | Description |
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| MKEX | Expiry | ||
| MKEX | Expiry |
Effective date: 20041207 |