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Description  |
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FIELD OF THE INVENTION
This invention concerns videocassette recorders (VCR's) equipped with VPT
(VCR Programmed by Teletext).
BACKGROUND OF THE INVENTION
It is well known that very often problems occur when a user attempts to
program his VCR to record a television show at a given time and date. To
eliminate these problems VPS (Video Program System) and VPT (VCR
Programmed by Teletext) were introduced. These systems are in common use
in Europe. VPT was formerly known as VPV (Videotext Programmed VCR).
The original purpose of adding a supplementary VPS signal to the
image-representative TV broadcast signal was to simplify the use of home
videocassette recorders (VCR's). Prior to the introduction of VPS, these
VCR's were programmed by means of a timer, which started and stopped the
VCR according to the time when the desired television program of interest
was scheduled for transmission.
Occasionally, the program of interest could not be correctly recorded, for
example, due to a delay in the completion of the previous television
program. The VPS signal was intended to overcome this drawback by
providing an accurate indication of the starting time of a new program. A
more detailed description is available in the literature, (see for
example, "VPS-Ein neues System Zur beitragsgesteuerten
Programmaufzeichnung", Rundfunktech-nische Mitteilungen, Heft 4,1985).
The VPS program identification code occupies four bytes (11-14) on data
line 16 in the vertical blanking (retrace) interval of a TV broadcast
signal. The four bytes of the VPS signal contain information such as day
and time of day of the originally scheduled start of a particular TV
program to be broadcast. A more detailed description of the VPS signal is
provided below.
To make the programming of VCR's even more convenient, the VPT system was
developed (see "Videotext programmierte Videoheimgerate (VPV)"
Rundfunktechnische Mitteilungen, Heft 3, 1986).
VPT involves the automatic transfer of the necessary information to a VCR
from the program pages of the teletext service. The user causes the
display of a directory of teletext program pages, and moves a cursor to
the desires television program title. Upon pressing an appropriate button
on a remote control, the necessary VPS program identification information
is transferred to the VCR.
It should be mentioned that the scheduled time and the VPS-time are not
always identical. This is because the scheduled time is updated whenever a
particular program runs overtime and subsequent programs are delayed or a
schedule is otherwise changed. The VPS time always remains unchanged since
it is assigned to the program and not to the actual final broadcast time.
By use of VPS and VPT, incorrect recording of a desired television program,
caused either by time-shifted television programs or by errors made by
manual keying in of the data such as start time stop time, date, and
program source (channel), is thus greatly eliminated.
Unfortunately, even if the VPS and VPT systems are used, the recording of
the desired television program can still fail because of VPT or VPS errors
originating from the studio side. Television programs are announced on VPT
program schedule pages two weeks in advance. If such a page contains
incorrect VPS data and a VCR is programmed with the incorrect data, the
recording of that particular television program will, of course, fail.
Usually, such errors are noticed and corrected by the editors of these
pages sometime after the incorrect data is entered. Even though such
errors are later corrected on the VPT pages by the editor, a conventional
VCR cannot adapt its preprogrammed data to such corrections. Another
source of errors which may prevent the recording of desired television
programs is the entry of incorrect VPS codes onto data line 16, also
caused by mistakes made at the broadcaster side.
SUMMARY OF THE INVENTION
It is herein recognized that conventional VPT programming and recording
control can be complemented with an error detection and correction
procedure to provide immunity against the above mentioned errors.
Conventional VPT/VPS recorders merely compare the incoming VPS data with
preprogrammed data sets. The recording starts as soon as a matching pair
of data is found and stops at the moment the data differ.
It is further herein recognized that preprogrammed data sets should be
compared continuously with the data on the latest actual teletext TV
program schedule pages. If differences between the two are detected, the
preprogrammed data are automatically adapted to the newer data. In this
manner, an error which was on a program page at the moment of programming
the VCR (and therefore transferred to the programming data memory) is
automatically detected and corrected.
It is also herein recognized that the incoming VPS codes should also be
continuously compared with the data on the corresponding teletext pages
containing the day's TV program schedule. The controller reacts in a
suitable manner in case of discrepancies of the data. Incorrect VPS codes
transmitted along with the program are thus also detected and corrected.
With these two additional procedures a fault tolerant recording control is
established and a correct recording of the desired programs guaranteed.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 shows a simplified block diagram of a VCR with VPT suitable for use
with the invention.
FIG. 2 shows a display of a VPT teletext page, which contains VPT
information as is known from the prior art.
FIG. 3 shows a display generated by a VCR according to the subject
invention.
FIG. 4a shows an example illustrating a problem occurring in a prior art
conventional VCR.
FIG. 4b shows screens illustrating operation according to the subject
invention.
FIG. 5 shows further examples of display screens illustrating operation
useful for understanding the subject invention.
FIG. 6 shows screens illustrating operation according to the subject
invention.
FIGS. 7-9 are flowcharts of program instructions suitable for execution by
microcomputer 150 of FIG. 1.
FIG. 10 shows a pictorial representation of two fields of video signals
including teletext and VPS data.
FIG. 11 shows a detailed view of a portion of television line 16.
DETAILED DESCRIPTION OF THE DRAWING
Referring to FIG. 1, a VCR includes a tuner 100 for selecting a particular
television signal from a plurality of television signals received by an
antenna 105. Tuner 100 operates under control of a system controller
microcomputer 110. System controller microcomputer 110 also controls the
various motors, actuators, and sensors 115 of the mechanical portion of
the VCR (not shown). System controller microcomputer 110 receives data
entered by a user from one of two sources, either from remote control unit
120 via remote control (RC) receiver 125, or from a locally-mounted key
pad 130. System controller microcomputer 110 also generates signals for
controlling a display module 135. The components described thus far are
standard television signal processing elements of commonly available
VCR's.
In addition to the television signal processing elements described above,
the VCR of FIG. 1 also includes teletext processing elements 140-160.
Tuner 100 supplies a composite video and blanking signal (CVBS) to a VPS
Data Line Receiver unit 140 (such as a Siemens SAA 4700) and to a Teletext
Data Slicer unit 145 (such as a Seimens SDA 5231). It is also possible to
omit separate VPS data line receiver 140 if a teletext data slicer with
built-in VPS decoder is used (such as a Seimens SDA 5645).
Teletext Data Slicer unit 145 separates the serial teletext data stream
from the composite video signal and routes the teletext signals to a CCT
Teletext Processor unit 155 (such as a Siemens SAA 5243) (CCT=Computer
Controlled Teletext decoder). CCT Teletext Processor 155 stores decoded
teletext data in a page memory unit 160. VPS Data Line Receiver unit 140
extracts VPS codes from the accompanying image-representative composite
video signal.
A VPT controller microcomputer 150 oversees all teletext functions,
controls the user-programming of the VCR, provides communication with the
user and also controls the recording of preprogrammed items.
Alternatively, separate VPT controller microcomputer 150 may be omitted if
VCR host system controller 110 is powerful enough to handle the additional
functions. Communication between CCT Teletext Processor unit 155, VPS Data
Line Receiver unit 140, and VPT controller microcomputer 150 is handled
over an IIC bus (sometimes called an I.sup.2 C bus). For more information
on the I.sup.2 C bus reference should be made to the Philips Technical
Publication of 1986 entitled "I.sup.2 C Bus Specification".
FIG. 2 shows a VPT teletext page, which contains in addition to start and
stop time and the title, the so-called VPT information reflecting the VPS
code of each program and consists of the program source code, the VPS-date
and the VPS-time. After acquiring such a page, the item to be
preprogrammed for recording is selected by means of a cursor. VPT
controller 150 then transfers all recording data (the complete VPS label,
start and stop time and the first row of the title) into the program
memory, which can be a part of teletext page memory 160. It is displayed
to the user on request, as shown in FIG. 3.
In conventional implementations, the recording controller continuously
reads all incoming VPS codes out of the VPS decoder and compares them with
the preprogrammed data. Recording is started when a matching pair is found
and is stopped at the moment the data differs again. For such VPS
recordings, a single error is fatal because VPS uses bit-pattern
comparisons and any mismatch disables the desired recording.
The procedures that provide the fault tolerance always require the most
current version of the actual TV program schedule pages. Each day, when
the first program is transmitted, its VPS code is used to find the pages
that contain the day's TV program schedule by means of the search
algorithm described in EPO patent application no. 90107169.6 (published as
EP 0 393 555). This procedure is followed for each channel. Once these
pages have been found, they can always be acquired again for the rest of
the day by using the page numbers determined at first reception.
As noted above, one aspect of the invention is to detect programming errors
that result from incorrect VPS data on the VPT page at the moment of
programming. This is accomplished by continuously comparing preprogrammed
data with the data in the TV program schedule pages and by adapting any
update. To this end, controller 150 continuously searches for the
preprogrammed VPS codes within the TV program schedule pages.
If no matching VPS code is found for such a preprogrammed item, then the
editor must have corrected the VPS code of the corresponding program in
the meantime. Because, in addition to the usual programming data, the
title of the desired program was also stored, controller 150 is able to
find the corresponding program on the VPT pages by using the relevant
title as a search argument. As soon as a program with a matching title is
found, controller 150 replaces the preprogrammed data with the corrected
VPS code from the VPT page. In this manner, all programming data are
updated to the latest schedule.
FIG. 4a shows an example of the operation of a conventional VCR with VPS
and VPT capability. FIG. 4b shows operation of the supplementary procedure
of the fault tolerant VCR, as described above.
Referring to FIG. 4a, on Jul. 26, 1990, a VPT page 410 is transmitted
showing the television schedule for a particular broadcaster (ZDF) for
Aug. 3, 1990 (i.e., one week ahead). A user moves a cursor to the entry
for the television program "Die Pyramide". By pressing the appropriate key
of remote control unit 120, the user instructs the VCR to program itself
with the data necessary to record the television show "Die Pyramide" as
shown in a screen display 420. Unfortunately, in this example, the editor
of that particular page inadvertently typed an incorrect VPS-time code
(i.e., 2055 instead of 2050). As a result, the VCR is now programmed with
incorrect data. Note that there are two columns of times shown in screen
display 410. Time column 411 contains the VPS-codes which correspond to
the originally scheduled start times of the various television programs
which are assigned when the schedule is written, i.e., the VPS-codes. Time
column 412 contains the actual starting times of the television programs.
The VPS time codes are never changed and serve to identify each program.
The actual starting times may be changed if, for example, the previously
scheduled program was a sporting event which ran over time. Thus, it is
perfectly acceptable for the VPS time and the actual start time to differ
from each other.
Screen display 430 shows a VPS schedule page transmitted on Aug. 2, 1990,
showing the television schedule for the same broadcaster (ZDF) for Aug. 3,
1990 (i.e., now only one day ahead). Note that the editor of the schedule
page has noticed his error, and has changed the VPS time to the correct
VPS time of 2050. Remember that the VCR has already been programmed to
search on Aug. 3, 1990 for the television program identified by the VPS
time code of 2055, and to begin recording when such program is found. On
Aug. 3, 1990, the broadcaster will transmit the television program "Die
Pyramide" with the correct VPS time code identifier of 2050 (because the
mistake has been corrected). Unfortunately, there will be no
correspondence between the transmitted VPS time code of 2050 and the
preprogrammed time code in the VCR (because the program memory in the VCR
still contains the erroneous VPS time code data), so as a result, nothing
will be recorded.
The operation of a fault-tolerant VCR according to the subject invention
will now be explained with reference to FIG. 4b. VPS screen displays 450
and 470 show the same VPS schedule page transmitted on Aug. 2, 1990, but
each is highlighted to draw attention to different data entries. In the
fault-tolerant VCR according to the subject invention, controller 150
continuously searches the received teletext pages for entries
corresponding to preprogrammed VPS codes. VCR programming screen 460
illustrates that three television shows have been programmed for
recording. In this example changes have been made to two of the three
entries. VPS schedule page 450 shows that the title of the Eurocops
episode "Der Erpresser" has been added. The VPS time code 2000,
corresponding to that entry will be found during a search by controller
150, and the preprogrammed information for that show will be updated to
reflect the corrected title, as shown in screen display 460. VPS schedule
page 470 shows that the incorrect VPS time code 2055has been changed to
the correct entry of 2050. A search of VPS time codes by controller 150
will no longer find an entry for 2055. In response to the failure to
detect this preprogrammed time code, controller 150 searches the VPS
schedule pages for Aug. 3, 1990 for that particular broadcaster for an
entry containing the title "Die Pyramide". Upon finding the title, the new
VPS time code is entered. Thus, on Aug. 3 1990 the correct VPS code will
be transmitted when the television show begins, and the television show
will be correctly recorded.
(For simplification, the search can be restricted to those preprogrammed
items, that are scheduled to be transmitted on the present day. The
controller thus only searches for a matching VPS code within those pages
that contain that day's TV program schedule).
Another aspect of the invention is to detect wrong VPS codes transmitted
within the signal. That is, the VPS code associated with the currently
running television program. To detect such errors the controller checks if
the incoming VPS code is contained on the actual TV program schedule pages
and thus represents a scheduled program. This is always done when the VPS
code changes, which usually signifies the end and/or beginning of the next
program, but can also occur erroneously during a program. If an incoming
VPS code is not found on the TV program schedule pages, there are two
possible reasons:
1. A wrong VPS code is transmitted and therefore this VPS code cannot be
found on the TV program schedule pages. In this case, the controller
replaces the wrong VPS code by the VPS code according to the program
schedule, assuming that the latter is the correct code. The recording is
then controlled by this corrected VPS code.
2. The VPS code represents a program, inserted on short term (e.g., a
newsworthy event), which is therefore not yet listed on the program
schedule pages. The controller reacts in this case in the same manner as
described above, as the controller cannot differentiate between these two
cases. But this does not matter, as usually, sooner or later, such
inserted programs are announced on the TV program schedule pages,
especially if they have a longer duration. In this case the controller
then finds the VPS code, which was assumed to be wrong, on an updated page
and concludes that the schedule change was due to an inserted program. In
case recording was initiated before by a "corrected" VPS code, the
controller will rewind the tape to the corresponding position.
Alternatively, recording with a different (corrected) VPS code can be
maintained at least as long as the remaining tape is sufficient to record
the remaining preprogrammed items.
FIG. 5 shows an example of the above-given operation. Teletext page 510 is
transmitted at 20:00, containing a schedule for that day's programming.
VCR programming page 520 shows that three of these television shows have
been preprogrammed for recording. No schedule changes are indicated on
screen display 510. At 20:00 the VPS time code (1D102 0308 2000) for the
television program "Eurocops" is detected and that show is recorded. At
20:50 a television show bearing an erroneous time code (1D102 0308 2051)
is transmitted. In a conventional VCR, nothing would be recorded because
the VPS time code does not match the preprogrammed time code for the show
"Die Pyramide" (1D102 0308 2050). However, in apparatus according to the
subject invention, if controller 150 does not find the VPS code of the
currently broadcast television program in the current VPT page, controller
150 concludes that the received code is incorrect, and replaces it with
the VPS code according to the schedule. In this example, the received code
(1D102 0308 2051) will be replaced by the code from the schedule (1D102
0308 2050) and the recording of the show will be initiated. At 21:45
nothing will be recorded because the television show "heute-journal" was
not selected for recording by the viewer (as shown in VCR programming
screen 520).
At 22:15 a television show entitled "Aktuell IRAK", and assigned a VPS time
code of 2216 is transmitted. As can be seen from schedule display screen
510, this television show was not scheduled, but nevertheless has been
inserted. Note that VPS time code 2215 could not be assigned to "Aktuell
IRAK" because that VPS code is already assigned to the television show
entitled "Aspekte". At 22:15 controller 150 detects the received time code
(1D102 0308 2216). As explained above, controller 150 will not find the
VPS code of the currently broadcast television program ("Aktuell IRAK") in
the current VPT page, and will conclude that the received code is
incorrect, and will replace it with the VPS code according to the
schedule. In this example, the received code (1D102 0308 2016) will be
replaced by the code from the schedule (1D102 0308 2015) and the recording
of the show will be initiated. At 22:21, a new VPS schedule page 530 is
transmitted, containing the corrected schedule showing the insertion of
the television program "Aktuell IRAK" at 22:15, bearing the VPS
identification code 1D102 0308 2016, and the delaying of the following
programs. In response, controller 150 finds the code of the currently
running program in the updated VPT page, and concludes that it is an
inserted television program. The recording is then stopped and controller
110 rewinds the tape. At 22:30 the television show "Aspekte" begins, its
VPS code is detected, and the show is properly recorded, even though it
began after a 15 minute delay from its originally scheduled time.
It is important to note that, as a result of the above-described
procedures, a correct recording is made even though the editor has not
corrected incorrect VPS data on the TV program schedule pages. This
results from the fact that controller 150 corrects an incoming VPS code
according to the schedule if it is not found on the TV program schedule
pages. This happens if a correct VPS code is transmitted, but the VPT page
contains an incorrect VPS code. In this case, the VPS code is corrected to
the wrong code from the page, but as the preprogrammed code coincides with
the incorrect code, a correct recording is made, as shown in FIG. 6.
In FIG. 6, a teletext VPS schedule page 610 containing an incorrect VPS
time code (2055 rather than 2050) is used to program a VCR. VCR
programming page 620 shows that the incorrect VPS time code 2055 has been
stored in memory. In this case, assume that the editor of the schedule
page does not notice and correct his mistake. At 20:50 the television show
"Die Pyramide" begins and its correct VPS identification code 1D102 0308
2050 is detected. In a conventional VCR with VPS and VPT capability
nothing would be recorded, because there is no correspondence between the
VPS time code stored in the VCR (1D102 0308 2055) and the transmitted VPS
time code (on television line 16) for the currently running program (1D102
0308 2050). In contrast, in apparatus according to the subject invention,
controller 150 will not find the VPS code for the currently running
television program in the current VPS schedule page. Controller 150 will
therefore conclude that the VPS code for the currently running program is
incorrect, and will replace it with the VPS code according to the
schedule. The television show corresponding to the VPS time code of the
current time slot (i.e., 20:50 on Aug. 3, 1990) was preprogrammed for
recording. Therefore, recording is initiated. Thus, even though the
programming error on the VPS schedule pages was not corrected, a VCR
employing the subject invention will nevertheless record the desired
television show properly.
FIG. 7 shows a simplified flow chart of the recording control software for
controller 150, which is suitable for use with the invention. It is just
an example for such an implementation, as the structure of the flow
control depends strongly on the other parts of the resident VCR controller
software.
Block 1: Read VPS code out of the VPS data line receiver.
Block 2: Check if the VPS code changed since the last read operation.
Block 3: The flow chart of this block is shown in FIG. 5.
Block 4: The flow chart of this block is shown in FIG. 6.
Block 5: Check if recording is in progress.
Block 6: Check if there is enough time to scan the tuner to another
pre-programmed station, or if a recording is expected soon on the present
station.
Block 7: Scan tuner to the next preprogrammed station.
FIG. 8 shows a flow chart of the procedure that detects and corrects errors
caused by incorrect data in the VPT-pages at the moment of programming.
Block 3.1: The teletext acquisition circuits and the related chapters of
the page memory have to be controlled such that all pages, containing
parts of the day's TV program schedule, are captured. The required
information (page numbers a.s.o.) is obtained from Block 4.2.
Block 3.1: Check if a new TV program schedule page has arrived.
Block 3.3: Check if VPS codes of preprogrammed items are contained in that
page.
Block 3.4: Check if the VPS codes of all preprogrammed items were found
within those pages, captured and analyzed until now.
Block 3.5: In case any non-VPS programming data (start time, stop time or
title)changed on the TV program schedule pages, these updates are adapted.
Block 3.6: Evaluate the VPS code of the next scheduled program, using the
captured pages. This "next" VPS code is required by Block 4.3.
Block 3.7: Check if the "next" VPS code, evaluated in Block 3.6, is valid.
It is only valid if this code was found on the same page that contains the
current program, or if tile start time of this "next" program corresponds
to the stop time of the current program or if all pages were captured at
the moment of evaluation.
Block 3.8: Check if all pages containing parts of the day's TV program
schedule have been captured and analyzed.
Block 3.9: Get the updated programming data of those preprogrammed items
not previously found when using their VPS code for search. These
programming data are now found by searching the corresponding programs in
the TV program schedule pages using the titles of the preprogrammed items.
FIG. 9 shows a flow chart of the procedure that detects wrong VPS codes
transmitted along with the program and provides the recording control.
Block 4.1: Check if it is the first VPS code received that day on that
station.
Block 4.2: Search the TV program schedule page that contains the current
program. Check also on which pages the rest of the day's schedule is
distributed, if rolling pages are used and capture the page numbers of
these pages. All this information is required by Block 3.1. During this
search operation the controller must periodically read the VPS code from
the VPS data line receiver and check if the corresponding program has to
be recorded.
Block 4.3: Check if that new VPS code corresponds to the expected "next"
VPS code obtained from Block 3.6.
Block 4.4: The controller checks if the VPS code is on the day's TV program
schedule pages.
Block 4.5: The controller replaces the received "wrong" VPS code by the VPS
code corresponding to the schedule.
Block 4.6: Check if the remaining tape is sufficient to record the
remaining preprogrammed items.
Block 4.7: The corrected VPS code is compared with the preprogrammed codes.
Recording is started or maintained if a matching pair is found. In case of
no coincidence the recording is stopped if recording is in progress.
Block 4.8: Read VPS code out of the VPS data line receiver.
Block 4.9: Check if a record was made with a "corrected" VPS code.
Block 4.10: Check if the recorded program was an inserted program.
Block 4.11: Rewind the tape to the corresponding position.
Block 4.12: The original VPS code is compared with the preprogrammed codes.
Recording is started or maintained if a matching pair is found. In case of
no coincidence the recording is stopped if recording is in progress.
FIGS. 10 and 11 may be useful in understanding the VPS system. FIG. 10
shows that the VPS signal for the currently running program is encoded on
television line 16. FIG. 11 shows a detailed view of the VPS information
content of television line 16.
It should be noted that the procedures of the subject application use those
teletext pages containing the current program schedule, and the software
must be able to find these pages within the teletext data system. As noted
above, the search algorithm described in EPO patent application no.
90107169.6 (published as EP 0 393 555) is suitable for that purpose.
The term "television receiver" as used herein includes television receivers
including a display means (commonly known as television sets", and
television receivers without display means, such as VCR's.
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