Editing SCART (section)

== Features ==

The SCART system was intended to simplify connecting AV equipment (including TVs, [[Videocassette recorder|VCRs]], [[DVD player]]s and [[video game console|games consoles]]). To achieve this it gathered all of the analogue signal connections into a single cable with a unique connector, which normally made incorrect connections nearly impossible.

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. A TV can be awakened from standby mode, and it can automatically switch to appropriate AV channel, when the device attached to it through a SCART connector is turned on.

=== Daisy chaining ===
[[File:Scartsocks.jpg|thumb|left|Typical SCART sockets on a set-top box]]

SCART is bi-directional regarding standard composite video and analogue audio. A TV 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. This allows "transparent" set-top boxes, without any tuner, which just "hook" and pre-process the TV signals. This feature is used for analogue pay TV like [[Canal+ (French TV provider)|Canal Plus]] and was used for decoding [[teletext]].

A VCR will often have two SCART sockets, to connect it to the TV ("up", "primary" or "1"), and for video input from a set-top box or other device ("down", "secondary" or "2"). When idle or powered off, VCRs will usually forward the signals from the TV to the set-top decoder and send the processed result back to the TV. 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 TV for viewing or simple recording control. Alternatively, the VCR could use the signals from the TV, in which case it would be inadvisable to change channels on the TV during the recording.

The "down" socket can also be used to connect other devices, such as DVD players or game consoles. As long as all devices have at least one "down" and "up" socket, this allows for connecting a virtually unlimited number of devices to a single SCART socket on the TV. While audio and video signals can travel both "up" to the TV and "down" to devices farther away from the TV, this is not true for RGB (and non-standard {{YPbPr}}) signals, which can only travel towards the TV.

"Down" and "up" are conventional. Logically, the TV is the last device of the "up" chain-path (stream) and the first device in the "down" chain path. Physically, the TV is under the device which sits on its top, hence the name "set-top box" for the device. Moreover, some sockets' relative position may enforce the belief that the TV is physically the last in the down direction.

Logically, the TV is on top and ends the "up" chain-path, translating the electrical info into an image and sound. From the same logical point of view the info stream, wherever it originates, may need processing such as decrypting (decoding, descrambling) or adding captioning/subtitles. In this case the info stream is sent logically "down" to dedicated function devices. From the last processing device the info stream is sent logically "up" to the TV, through all the chain-path. Another case is when the info stream is sent "down" and not expected to be sent back "up", for example when sent to a recorder.

Closing a loop on either the "up" or "down" chain-path may not have useful effects and may create instability.

=== Direct connections ===

As audio and (composite) video use the same pins on "down" and "up" connectors (and require a crosslinked cable), it is also possible to connect two devices directly to each other without paying attention to the type of the socket.

However, this no longer works when S-Video signals are used. As straight links (RGB red and blue up) were re-purposed to carry chrominance information, the S-Video pinouts are different for "down" and "up" SCART connectors.<ref>{{Cite web|url=http://www.camp0s.com/pc_related/svideo/svideo.php|archive-url=https://web.archive.org/web/20111008112024/http://www.camp0s.com/pc_related/svideo/svideo.php|url-status=dead|title=S-Video to SCART signal conversion guide|archive-date=October 8, 2011}}</ref> Further, they are often not fully implemented.

Paying attention to the type of socket is essential when handling component RGB/{{YPbPr}}/S-video. Damage can be caused to devices incorrectly connected as follows:
*connecting SCART 1 ("up") from one device to SCART 1 ("up") of another device when both SCARTs are configured for RGB/{{YPbPr}}/S-video-up. Pins 7, 11 and 15 are outputs.
*connecting SCART 2 ("down") from one device to SCART 2 ("down") of another device when both SCARTs are configured for S-video-down. Pin 7 is an output.
*connecting SCART 1 ("up") from a device configured RGB/{{YPbPr}}, to SCART 2 ("down") of another device configured with S-video-down. Pin 7 is an output.

Damaging pins 7, 11 or 15 may result in yellow, purple or blue/green images, due to the missing blue, green or red components respectively. When using S-video, damaging pin 7 or 15 may result in black-white images due to the missing chroma component ("down" and "up" respectively). Similarly, damaging pins 7 and 15 (P<sub>B</sub> and P<sub>R</sub>) while leaving pin 11 (Y) undamaged may result in black-white images when using {{YPbPr}}. Damaging more than one of these pins may result in combined effects.

=== RGB overlays ===

SCART enables a device to command the TV 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 TV to stop displaying the normal signal and display a signal it generates internally for selected image areas, with [[pixel]]-level granularity. This can also be driven by the use of a "transparent" color in a teletext page.

=== Device control ===

SCART allows a connected device to bring it in and out of ''standby'' mode or to switch it to the AV channel. A VCR or other playback device will optimally power on when a cassette is inserted, power on the TV (or switch it to video mode) and then start playing immediately if the cassette write protection tab is absent. When turned off, the VCR will ask the TV to power off, which it will do if it had been powered on by the VCR's request and if it remained in video mode. Only some TVs will do this—most only implement automatic switching to and from the SCART input.

The same signal can be used by a [[Satellite television|satellite]] receiver or [[set-top box]] to signal a VCR that it is supposed to start and stop recording ("pin 8 recording"). This configuration usually requires that the VCR be farther from the TV than the source, so the signal usually travels "down".