FBI
Field blanking interval. In a television signal, the interval
between the fields of video information. It is now preferred to
VBI, vertical blanking interval.
flash
A display
mode in which the display of a character(s) alternates with the
display of a space(s) under the control of a timing device in the
decoder.
FLOF
Full level
one features, a term used during the development of level 2 WST.
FM
Frequency
modulation, a modulation method where the frequency of the
carrier signal is changed in response to the modulating signal,
the carrier amplitude being kept constant.
foreground colour
The colour of alphanumerics or graphics.
framing code
A
byte following the clock run-in sequence which allows the
receiver to achieve byte synchronization. In WST it is so
protected that it may be currently decoded even if one of its
bits is wrongly decoded.
graphics character
One of the 64 different display characters based on the division
of the character rectangle into six cells. The cells can be
displayed contiguously or separated.
graphics mode
The display mode in which the display characters are those of one
or the other graphics sets depending on whether the contiguous or
separated mode is being used.
Golay code
A
forward error connecting code. In the (23 12) form used in the
MAC/packet system, Golay code allows for the correction of up to
three errors in the group of 23 bits.
ghost-rows
An
early term for an additional row that was not intended to be
displayed but which contained additional control information for
the page.
Hamming code
A
forward error-correcting code, due to Hamming. Several versions
are used in WST. At level 1 the Hamming code is a byte containing
four message bits and four protection bits. Hamming codes are
used to protect address or control information and, in the stated
form, are able to correct the error in the byte.
handshake
An
exchange of signals used in communication protocols to indicate
that the previous part of the signal had been received
successfully and that the next part can be sent.
hold graphics
A
mode of graphics display in which any control character occurring
during the graphics mode results in the displayed graphics
character being held to cover the space occupied by the next
control character. Its use allows the avoidance of space which
would otherwise occur between changes of graphics colour.
IBA
Independent
Broadcasting Authority.
IRT
Institut
fiir Rundfunktechnik (Germany). linked pages Pages which contain
information which link them to another page. Packet
27 is designed to carry information of this type.
LSI
Large scale
integrated circuit, a complex device in which a large number of
semiconductors are deposited on one piece of silicon usually to
perform a particular task.
magazine
A group
of up to 100 numbered pages, each carrying a common magazine
number in the range 1 8. Up to eight magazines may be
transmitted in series or parallel on a television channel.
network identification
Part of the broadcast service packet 8/30.
newsflash page
A page in which all the information for display is boxed so that it
can be seen better against the television picture. Control bit C5
is set to indicate to the decoder that the information should be
inset into the television picture or added to the television
picture.
NRZ
Non-return-to-zero, a form of coding for data in which the data
stays in the one position until the next zero data
pulse causes it to return to zero.
ORACLE
The name
of the UK independent television companies teletext service.
page
A group of
up to 24 rows of 40 characters intended to be displayed as an
entity on the television screen.
page header
A
page header data line has a row address 0 and it separates the
pages of a magazine in the sequence of transmitted data lines. In
place of the first eight-character byte, it contains Hamming
coded address and control information relating to the page. Thus
the top row of the page has only 32 display character bytes.
These are used for the transmission of general information such
as magazine and page number, day and date, programme source and
clock time.
page subcodes
An
addition to the page numbers to extend the page address range.
PDC
Programme
Delivery Control, the control of domestic videocassette recorders
by teletext packet 8/30.
RDS
Radio Data
System, a method of adding a sub-carrier signal to the normal FM
stereo radio signal for the transmission of digital data.
release graphics
The display mode in which control characters are invariably
displayed as spaces. It is complementary to the hold graphics
mode.
reveal
The
display mode complementary to the conceal mode.
rolling headers
The use of the top row of the page to display all the page
headers of the selected magazine as they are transmitted. This
gives an indication to the viewer of the page
transmission sequence, watching or awaiting a selected page.
RS232-C
Electronic Industries Association (EIA) standard applicable to
the interconnections between data terminal equipment (DTE) and
data communication equipment (DCE) employing serial
communications. The C indicates the latest revision
and the standard is usually referred to as RS232. (See Appendix
for application details.)
row
A page comprises 24 rows of characters. When displayed on a
television screen each row occupies about 20 television lines. To
avoid confusion with television lines the lines of
text are called rows.
row adaptive transmission
Teletext transmission in which rows containing no information are
not transmitted rather than being transmitted as a row of space
characters. This reduces the access time of the transmission. The
non-transmitted rows are displayed as unboxed black spaces.
separated graphics set
The set of 96 display characters comprising the 64 separated
graphics characters (corresponding to the contiguous graphics
characters) together with the 32 alphanumeric characters.
separated graphics mode
The display mode in which there is background colour boundary
around and between the six cells of the graphic characters within
the character rectangle.
smoothed graphics
A graphics set available in the higher levels of WST, giving
better resolution graphics.
space
A
character rectangle entirely filled by the background colour.
sub-carrier
An
additional carrier signal for transmission of supplementary
information.
subtitle page
A
page in which all the information for the display is boxed and
the control bit C6 is set to allow the decoder to automatically
inset or add to the television picture.
teletext
A method of transmitting data, usually in the field blanking
interval of a television signal.
television data line
See data line.
time coded page
A page containing a time code in the header, and transmitted at a
pre-set time.
time display
The
last eight characters of every page header are reserved for
clock-time. A receiver may be arranged to display these
characters to give a clock-time display as an insert into the
picture.
VBI
See FBI.
videotext
This
is the general name used for an information service that uses a
telephone line for the transmission of the data.
WST
World System
Teletext.
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