SCART

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Image:SCART 20050724 003.jpg Template:Commons 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 SCART word is not normally used) and Euroconnector.

SCART makes it easy to connect AV equipment (including TVs, VCRs, DVD players and games consoles) with optimal quality. 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 video, and stereo audio input/output, as well as support functions.

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.

1 Motivations and applications for SCART
2 Drawbacks
3 Practical advice
4 Pinout
- 4.1 Blanking and Switching
5 See also
6 External links

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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 VHS VCR could output a composite video signal through a German-originated DIN-style connector, an American-originated RCA connector, or a BNC connector.

Image:Scartsocks.jpg

SCART attempts to make connecting video devices together much simpler, by providing one plug that contains all the necessary signals (refer to the Pinout below 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 you cannot insert it 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 pretty high, around 1V, 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 to have "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 2 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 unadvisable to change channels on the television set during the recording.

SCART also allows to instruct the television set to very quickly switch between signals, in order to create inserts 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 usage 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 was powered on on VCR's request and if it remained in video mode all along.

The standard was extended at the end of the 1980s to support the new S-Video signals.

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Drawbacks

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.
SCART cannot officially carry other non-RGB type (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 is not designed to transmit digital video or audio signals. The new (digital) audio+video HDMI connector is often referred to as "digital SCART". From this it appears that there will never be a second generation analog SCART to address the above limitations.
SCART is limited to two audio channels - meaning it cannot deliver true surround sound.
SCART connects are non-locking 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. To allow limited locking, some connectors (such as the one portrayed on this page) have bumps on the sides.
The connector design requires the plug to be perfectly aligned over the socket before it can be inserted at all, whereas most other connect designs are self-correcting if the plug is inserted at slightly the wrong angle.
Cheap SCART connectors can be very fragile and prone to breaking, losing pins, etc., since they are big and hollow.

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Practical advice

Nearly all DVD players with SCART sockets will 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 - this often has to be set manually in the player's setup menu or via switches on the back of the player.

The Nintendo GameCube, Sony PlayStation 2 and the Microsoft Xbox, can output RGB, Y-Cr-Cb, 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.

Maximum SCART cable length is estimated to about 10 to 15 meters without relay.

Quality differences exist in SCART cables. While a proper SCART cable would use 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. 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. A common problem is that a TV will output a composite video signal from its internal tuner, and this will be induced or cross-talk onto an incoming video signal due to inadequate or non-existent screening on a cheap SCART cable; the results will be ghostly images or shimmering superimposed on the incoming signal.

Gold plated SCART connectors, which don't corrode and deliver a cleaner signal might be preferable, although they always cost more than Nickel ones. It should be noted, though, that 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.

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Pinout

Extensions to the original standard are in italics. Input and output are defined with respect to the TV set.

Female:

+------------------------------------------+
| 1   3   5   7   9   11  13  15  17  19   | 21
|                                          \
|   2   4   6   8   10  12  14  16  18  20  \
+--------------------------------------------+

Male:

+--------------------------------------------+
|   2   4   6   8   10  12  14  16  18  20  /
|                                          /
| 1   3   5   7   9   11  13  15  17  19   | 21
+------------------------------------------+

Audio output, right
Audio input, right
Audio output, left
Audio ground
Blue ground
Audio input left
Blue
Function switching (see below)
Green ground
D²B input
Green
D²B output
Red/Chroma (C) ground
D²B ground
Red/Chroma
Fast switching (see below)
Composite video ground/sync ground/Luminance (Y) ground
Fast switching ground
Composite video output/sync output/Luminance (Y) output
Composite video input/sync input/Luminance (Y) input
Common ground (metal shield)

D²B (Digital Data Bus) is an IEC standard for a serial communication bus. It is a multi-master bus for home automation, and was originally developed by Philips in the 1970s.

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Blanking and Switching

Two pins provide switching signals.

Pin 8, the function switching pin, carries a low frequency (less than 50Hz) signal from the source that indicates the type of video present.

0V-2V means no signal, or internal bypass

4.5V-7V (nominal 6V) means a widescreen (16:9) signal

9.5V-12V (nominal 12V) means a normal (4:3) signal

Pin 16, the fast switching pin, carries a signal from the source that indicates that the signal is either RGB or composite.

0V-0.4V means composite.

1V-3V (nominal 1V) means RGB only.

The original specification defined pin 16 as fast blanking, a high frequency (up to 3MHz) signal that blanked the composite video. The RGB inputs were always active and the fast blanking signal 'punches holes' in the composite video. The SCART connector use this to overlay subtitles from an external Teletext decoder.

0V-0.4V means composite with a transparent RGB overlay.

1V-3V (nominal 1V) RGB only.

There is no switching signal to indicate S-Video. Some TVs can autodetect the presence of the S-Video signal but more commonly the S-Video input needs to be manually selected.

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