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SCART (from Syndicat des Constructeurs d'Appareils Radiorécepteurs et
Téléviseurs) is a French-originated standard and associated 21-pin connector for
connecting audio-visual equipment together. It is also known as Péritel
(especially in France, where the term SCART is not normally used), 21-pin
EuroSCART (Sharp's marketing term for an attempt to market the connector in the
Asian region) and Euroconnector.
The SCART connector first appeared on television sets in 1977. It became
compulsory on all new television sets sold in France starting from January 1980.
SCART makes it easy to connect AV equipment (including TVs, VCRs, DVD players
and game consoles). In essence, it gathers together various common analog signal
types into a single connector. Previously, each of these would have had their
own socket, requiring numerous separate connections and a "spaghetti" type mass
of leads. The signals carried by SCART include both composite and RGB (with
composite synchronisation) video, stereo audio input/output and digital
signalling. The standard was extended at the end of the 1980s to support the new
S-Video signals. In addition, a TV can be awakened from standby mode or switched
to video mode through a SCART connector.
In Europe, SCART is the most common method of connecting audio-visual equipment
together, and has become the standard connector for such devices (even more so
than the phono plug). It is far less common elsewhere in the world.
The official standard for SCART is CENELEC document number EN 50049-1.
SCART is sometimes referred as the IEC 933-1 standard.
Motivations and applications for SCART
Before SCART came, consumer TV sets did not offer a standardized way of
inputting signals other than RF antenna ones, and even antenna connectors
differed between countries. Assuming other connectors even existed, devices made
by different companies could have different and incompatible standards. For
example, a domestic VCR could output a composite video signal through a
German-originated DIN-style connector, an American-originated RCA connector, an
SO259 connector, or a BNC connector.
SCART attempts to make connecting video devices together much simpler, by
providing one plug that contains all the necessary signals (refer to the Pinout
to the right for details), and is standard across different manufacturers. SCART
makes connecting such devices very simple, because one cable can connect any two
SCART-compatible devices, and the connector is designed so that it cannot be
inserted incorrectly. Devices with multiple SCART connectors can pass the
signals unchanged when not active, which allows daisy chaining of multiple
signal sources into a single TV socket. The voltage levels are quite high,
around 1 V, so the signals have good noise immunity.
SCART is bi-directional regarding standard composite video and analog audio. A
television set will typically send the antenna audio and video signals to the
SCART sockets all the time and watch for returned signals, to display and
reproduce them instead. This allows "transparent" set-top boxes, without any
tuner, which just "hook" and pre-process the television signals.
This feature is used for analog Pay TV like Canal Plus and was in the past used
for decoding teletext. A VCR will typically have two SCART sockets, one
connecting to the television set, and another one for the set-top box. When idle
or powered off, the VCR will forward the signals from the television set to the
set-top decoder and send the processed result back to the television set. When a
scrambled show is recorded, the VCR will drive the set-top box from its own
tuner and send the unscrambled signals to the television set for viewing or
simple recording control purposes. Alternatively, the VCR could use the signals
from the television set, in which case it would be inadvisable to change
channels on the television set during the recording.
SCART also enables a device to command the television set to very quickly switch
between signals, in order to create overlays in the image. In order to implement
captioning or subtitles, a SCART set-top box does not have to process and send
back a complete new video signal, which would require full decoding and
re-encoding of the color information, a signal-degrading and costly process,
especially given the presence of different standards in Europe. The box can
instead ask the television set to stop displaying the normal signal and display
a signal it generates internally for selected image areas, with pixel-level
granularity. This can be driven by the use of a "transparent" color in a
teletext page.
SCART allows a connected device to power on and power off a television set, more
precisely: to bring it in and out of standby mode, in the same way as a remote
control would do. A VCR will optimally power on when a cassette is inserted,
power on the television set (or switch it to video mode) and then start playing
immediately if the cassette's write protection tab is absent. When turned off,
the VCR will ask the television set to power off as well, which the set will do
if it had been powered on by the VCR's request and if it remained in video mode
all along. Only some TV sets will do this—most only implement automatic
switching to and from the SCART input.
Some of the most creative usages for SCART connectors appeared in analog
satellite receivers. The function of decoding hybrid, time-compressed
analog-digital MAC transmissions into RGB and analog audio was akin to making a
digital receiver out of an analog one. The D2B pins (10 and 12) were used for
communicating with satellite dish positioners and for driving magnetic
polarizers, before these became incorporated into LNBs. The daisy-chaining
features were used to connect both a Pay TV decoder and a dish positioner/polarizer
to a single Decoder socket on the receiver.
SCART supports automatic widescreen switching. This is an extension of the
functionality of a pin which previously only indicated to the TV set that an
external signal should be displayed. Ideally, a widescreen source should offer
three operating modes in order to deal with widescreen signals:
* either assume that the telewision set is widescreen or capable of otherwise
dealing with widescreen pictures,
* or assume that it is standard and not capable of dealing with widescreen
pictures, in which case one should allow the user the option to:
* either display the full image in letterbox format
* or display the center of the image, with sides truncated, as if zoomed into.
In the first case, the widescreen pin allows to indicate the current signal
format, which allows widescreen sets to adjust the image width, and
widescreen-capable standard sets to compress the image vertically. In the second
case, the widescreen SCART signal is never active and the signal source performs
the adaptations itself so that the image has always a standard format as a
result. In practice, some sources will assume that the television set is always
capable of widescreen functionality and hence never perform the adaptations.
Some source will not even issue the widescreen signal or maintain it at the same
level all the time. Other sources might offer the option of truncating the
sides, but not of letterboxing, which requires significantly more processing.
Notably, the circuitry of the early widescreen MAC standard decoders (eg. the
Visiopass) could not letterbox. The limitations apply mostly to satellite
television receivers, while DVD players can always at least letterbox and often
zoom.
Criticisms
* SCART cannot carry both S-Video and RGB signals at the same time. It is,
however, possible to output S-Video and RGB alternately, (for example, from an
S-VHS + DVD combo player), and the TV set will adapt automatically if it
understands SCART's S-Video extension. Many DVD players sold in Europe offer the
ability to output either RGB or S-Video, which is either selected in the DVD
player's set-up menu or by a switch on the back of the system.
* RGB connections are not bidirectional. Bidirectional S-Video was added in an
extension, although few devices support this, so downstream connections are
almost always composite.
* SCART is sometimes confusing for consumers. Some TV sets that have multiple
SCART connectors have only one capable of receiving RGB and the other one
capable of receiving S-video. Also, not all SCART cables make use of all the
pins, often leaving out RGB signals. In many cases there is also no way to see
which type of signal is currently displayed on the TV set. However, because of
compatibility with set top boxes, at least one SCART socket must be
full-featured, ie. both issue and accept composite video, and accept RGB video.
In recent years, non fully wired SCART cables tend to disappear from the market,
because modern devices systematically provide RGB signals, while composite-only,
analog VCRs and pay-tv decoders could not.
* SCART cannot officially carry non-RGB (e.g., YPbPr) component video signals,
which are gaining ground as an improvement over S-Video in markets where SCART
is not used. However, some manufacturers of set-top-boxes and DVD players are
known to provide optional (menu-selectable), non-standard YPbPr output through
the pins that are officially reserved for RGB color components.
* SCART connectors provide only limited locking, using detents, and are prone to
falling off or getting loose, especially since the thick 21-wire cable is
relatively heavy and often leaves the connector at a sideways angle. Loss of
audio or video connection due to a loose SCART connector is relatively common.
Depending on which end of the plug is loose, either a loss of audio (rectangular
end) or a loss of video (triangular end) is observed.
* The thickness and inflexibility of the cables, combined with the fact that
they are connected to the plugs at an angle, can sometimes make it difficult to
connect items of equipment, especially in confined spaces. Attempts at thinner
or flat cables are more susceptible to cross-talk, or are unable to support all
communication modes.
* The connector design requires the plug to be perfectly aligned over the socket
before it can be inserted at all, whereas more recent connector designs are
self-correcting if the plug is inserted at slightly the wrong angle.
* Cheap 10-pin SCART connectors can be very fragile and prone to breaking or
losing pins, since they are big and hollow. 21-pin connectors are generally
stronger.
* SCART connectors are large and cumbersome compared to most modern connectors
(such as HDMI) and the cabling is often bulky and heavy.
* Some of the SCART switching features are often poorly implemented although
this is often more due to deficencies in individual equipment design than any
inherent flaws in the SCART standard
Practical advice
Nearly all DVD players with SCART sockets output RGB video, which offers far
superior picture quality to typical composite signals. However, many players do
not have RGB output turned on by default but Composite video—this often has to
be set manually in the player's setup menu or via switches on the back of the
player.
Enlarge picture
High quality gold plated Péritel/SCART RGB AV coaxial cable for PlayStation 2.
The Nintendo GameCube, Nintendo Wii, Sega Dreamcast, Sony PlayStation 2, Sony
Playstation 3, Microsoft Xbox and Microsoft Xbox 360 can output RGB, YPbPr,
S-Video, or composite video. These consoles come with the standard composite
video connector, but the manufacturers and third parties sell connectors for
component video hookup and for RGB SCART hookup. Where the GameCube and Xbox
automatically switch to the proper mode, the PlayStation 2 must be told via a
selection in the system menu whether it is to use YPbPr or RGB component video.
Also, some versions of legacy consoles such as Nintendo's SNES and Nintendo 64
(some, modified NTSC models only) are capable of outputting RGB signals (using
the same cable as the GameCube).
Many older home computers (Amstrad CPC, later ZX Spectrum models, Commodore
Amiga, Atari ST, BBC Micro and Acorn Archimedes, etc.) output RGB with composite
sync suitable for SCART use, but most used varying non-standard DIN plugs.
Standard-resolution arcade monitors use RGB signals with a composite sync, which
is SCART-compatible.
Maximum SCART cable length is estimated to be about 10 to 15 meters without
relay.
Due to the relatively high voltage used in SCART, "hot plugging" (connecting or
disconnecting devices while they are on) is not recommended. Although there is
no risk of personal injury, there is the possibility of damaging electronics
within the devices if the connector is inserted improperly.
Quality differences exist in SCART cables. While a proper SCART cable uses
miniature coax cables for the video signals, cheap SCART cables often use plain
wires for all signals, resulting in a loss of image quality and greatly reducing
the maximum cable length. A common problem is that a TV outputs a composite
video signal from its internal tuner, and this is induced or cross-talked onto
an incoming video signal due to inadequate or non-existent screening on a cheap
SCART cable; the result is ghostly images or shimmering superimposed on the
incoming signal. To non-destructively verify if a SCART cable uses coax cables,
one can unscrew the strain relief at the SCART connector and fold open the
plastic shell.
Although using higher-quality cables might help in reducing a 'ghosting' effect,
a more permanent method is to remove pin 19 from the SCART plug that is put into
the TV. Pin 19 is Video Out, and removing it prevents a signal from being
broadcast by the TV into the cable in the first place, so it cannot cross-talk
with the incoming signal. Cheaper SCART plugs can sometimes have the pins pushed
inside the connector housing so as to remove it in a non-destructive manner (and
thus allowing for its replacement in the future should the need arise by simply
unscrewing the housing and pushing the pin back through its hole), though
sometimes the pins are fixed in place on the inside by glue or rubber and can
only be removed by forcefully twisting them off entirely. Generally though, for
a standalone TV there is no need for video output on the TV end of the SCART
plug, so in the majority of cases removing it completely should not be a
problem. Whichever way it is done, however, once it is the SCART is rendered
incapable of transmitting a video signal from that end of the cable, so it would
be wise to mark it as such for future reference.
Gold-plated SCART connectors, which do not corrode and deliver a cleaner signal,
might be preferable, although they always cost more than nickel ones. However,
gold-plated connectors only give better performance when both plug and socket
are gold plated. Gold and nickel are galvanically very different metals, and
although inserting a gold-plated plug into a nickel plated socket may make a
small difference at first, any atmospheric moisture that is present near the
connector will cause an electrolytic reaction between the dissimilar metals.
This will result in the nickel-plated connector corroding much more rapidly than
it would if both connectors were nickel-plated. For good long-term connection
quality it is always better to use matching connector materials.
Blanking and switching
Two pins provide switching signals.
Pin 8, the switch signal pin, carries a low frequency (less than 50 Hz) signal
from the source that indicates the type of video present.
0 V–2 V means no signal, or internal bypass
4.5 V–7 V (nominal 6 V) means a widescreen (16:9) signal
9.5 V–12 V (nominal 12 V) means a normal (4:3) signal
Pin 16, the blanking signal pin, carries a signal from the source that indicates
that the signal is either RGB or composite.
0 V–0.4 V means composite.
1 V–3 V (nominal 1 V) means RGB only.
The original specification defined pin 16 as a high frequency (up to 3 MHz)
signal that blanked the composite video. The RGB inputs were always active and
the signal 'punches holes' in the composite video. This could be used to overlay
subtitles from an external Teletext decoder.
0 V–0.4 V means composite with a transparent RGB overlay.
1 V–3 V (nominal 1 V) RGB only.
There is no switching signal to indicate S-Video. Some TVs can auto-detect the
presence of the S-Video signal but more commonly the S-Video input needs to be
manually selected.
Cables
An extension cable consists of a male plug at one end and a female socket at the
other. In an extension cable all the wires within the cable connect to the
identical pin number at each end.
The cables for connecting equipment together have a male plug at each end. Some
of the wires such as ground, data, switching and RGB connect to the identical
pin number at each end. Others such as audio and video are swapped so that an
output signal at one end of the cable connects to an input signal at the other
end. The complete list of wires that are swapped is: pins 1 and 2, pins 3 and 6,
pins 17 and 18, pins 19 and 20.
SCART leads are available to buy in a wide range of stores fairly cheaply.
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