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SCART

From Academic Kids

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Scart-plug.jpg
SCART plug

SCART (from Syndicat des Constructeurs d'Appareils Radiorécepteurs et Téléviseurs) is a French-originated standard and associated 21-pin connector for connecting audio and video equipment to television sets. Also called Péritel (especially in France, where the SCART word is not normally used) and Euroconnector. SCART makes it easy to connect VCRs, DVD players, set-top boxes (Pay TV, analog or digital cable, terrestrial digital TV), home computers, gaming systems and other equipment to television sets with optimal quality.

Contents

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 or through an American-originated RCA connector.

SCART attempts to make connecting video devices together much simpler, by providing one plug that contains all the necessary signals, 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 are effectively immune to noise.

SCART is bidirectional regarding standard composite video. A television set will typically send the antenna signal to the SCART sockets all the time and watch for a returned signal, to display it instead. This allows to have "transparent" set-top boxes, without any tuner, which just "hook" and process the television signal before it gets displayed.

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 signal 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 signal to the television set for viewing or simple recording control purposes. Alternatively, the VCR could use the signal from the television set, in which case it would be unadvisable to change channels on the television set during the recording.

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

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.
  • SCART cannot carry component video (Y-Cr-Cb) signals.
  • SCART cannot transmit a digital picture. 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 cannot transmit 5.1 or higher surround sound formats. In general, 5.1 sound is new to European TV; it only started to appear in 2004, on selected satellite channels.

Some people do not see an improvement in video quality by using component video rather than RGB; a more significant difference in quality is obtained when switching from composite over an antenna to S-Video/RGB/component over a cable (SCART or otherwise). However, component video is increasingly being recommended by reviewers of DVD players. The most likely benefit of using component video is reducing the possibility of bleed-through between the three components, since each has its own cable.

Certain game consoles, such as the Sony PlayStation 2 and the Microsoft Xbox, can yield RGB, component, S-Video, or composite output. These consoles come with the standard composite video connector, but the manufacturer or third parties sell connectors for component video hookup and for direct SCART hookup. In most cases, these direct SCART cables are wired for RGB as well as composite video. If one of these consoles is used with a direct SCART cable, the console must be configured for RGB rather than Y-Cr-Cb output in its "Component Video" menu.

For professional use, SCART has a few physical drawbacks:

  • The 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. Also, cheap scart connectors can be very fragile and prone to breaking, losing pins, etc., since they are big and hollow.
  • 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, unscrew the strain relief at the SCART connector and fold open the plastic shell.)

Pinout

Extensions to the original standard are in italics.

+------------------------------------------+
| 1   3   5   7   9   11  13  15  17  19   | 21
|                                          \
|   2   4   6   8   10  12  14  16  18  20  \
+--------------------------------------------+
  1. Audio output, right
  2. Audio input, right
  3. Audio output, left
  4. Audio ground
  5. Blue ground
  6. Audio input left
  7. Blue
  8. Function switching (see below)
  9. Green ground
  10. D²B input
  11. Green
  12. D²B output
  13. Red/Chroma (C) ground
  14. D²B ground
  15. Red/Chroma
  16. Vertical blank (VBL)
  17. Composite video ground/Composite sync ground/Luminance (Y) ground
  18. VBL ground
  19. Composite video output/Composite sync output/Luminance (Y) output
  20. Composite video input/Composite sync input/Luminance (Y) input
  21. Common ground (metal shield)

Pin 8, the function-switching pin, carries a signal from the source that indicates the type of video present.

0V means no signal, or internal bypass
+6V means a widescreen (16:9) signal
+12V means a normal (4:3) signal

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.

Speculations about the intentions of the creators of SCART

The original purpose of SCART, according to some, was to prevent foreign television imports. Previously France had legislation which prevented all imported televisions, if they didn't support the old French 819 line monochrome system. One could understand that this effectively stopped any foreign televisions being imported, but when the 819 line system disappeared (its VHF frequency band was given to Canal Plus, the first French Pay TV network, at the beginning of the eighties) this was no longer a valid reason for banning imports. Therefore they introduced the SCART socket to try to maintain their private television market [another speculation], the newly passed legislation requiring every TV sold in France since 1980 to have a SCART socket. This was of course much less of a deterrent, as it was much easier for manufacturers to add a SCART socket to their televisions than to produce dual-standard sets, and the SCART was actually useful elsewhere, with the development of home video recorders and especially of video games and home computers, which could be very easily connected to TV sets, giving the best possible image quality.

Another alleged reason was Minitel. Early prototypes did not have their own display; instead, they used the TV as their display, similar to games consoles. An RF interface would have provided lesser quality text. Originally, there were supposed to be many models of Minitel. In the end, only one major model shipped, and had a built-in small monochrome CRT.

See also

External links

  • SCART pinout (http://utopia.knoware.nl/users/eprebel/SoundAndVision/Engineering/SCART.html)de:SCART

fr:Péritel it:SCART nl:SCART pt:Syndicat des Constructeurs d'Appareils Radiorécepteurs et Téléviseurs fi:SCART uk:SCART

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