SCART
 A male SCART connector (21-pin) | |||
| Type | Analogue audio and video connector | ||
|---|---|---|---|
| Production history | |||
| Designer | CENELEC | ||
| Designed | 1970s | ||
| General specifications | |||
| Audio signal | Bi-directional Stereo | ||
| Video signal | Composite (bi-directional), RGB (uni-directional) or S-Video (sometimes bi-directional) | ||
| Pins |
21 (21 wires:RGB/10 wires:CVBS) 10 (10 wires:CVBS) | ||
| Data | |||
| Data signal | D²B and widescreen switching | ||
| Pinout | |||
 | |||
| Female connector seen from the front | |||
| Pin 1 | Audio output (right) | ||
| Pin 2 | Audio input (right) | ||
| Pin 3 | Audio output (left/mono) | ||
| Pin 4 | Audio ground | ||
| Pin 5 | RGB Blue ground (pin 7 ground) | ||
| Pin 6 | Audio input (left/mono) | ||
| Pin 7 |
RGB Blue up S-Video C down[a] Component PB up[b] | ||
| Pin 8 |
Status & Aspect Ratio up[c]
| ||
| Pin 9 | RGB Green ground (pin 11 ground) | ||
| Pin 10 |
Clock / Data 2[d] Control bus (AV.link) | ||
| Pin 11 |
RGB Green up Component Y up[b] | ||
| Pin 12 | Reserved / Data 1[d] | ||
| Pin 13 | RGB Red ground (pin 15 ground) | ||
| Pin 14 | Data signal ground (pins 8, 10 & 12 ground) | ||
| Pin 15 |
RGB Red up S-Video C up Component PR up[b] | ||
| Pin 16 |
Blanking signal up
| ||
| Pin 17 | Composite video ground (pin 19 & 20 ground) | ||
| Pin 18 | Blanking signal ground (pin 16 ground) | ||
| Pin 19 |
Composite video output S-Video Y output | ||
| Pin 20 |
Composite video input S-Video Y input | ||
| Pin 21 | Shell/Chassis[e] | ||
|
^ a rarely supported. up/down denotes links to/from the TV set | |||
 | This article needs additional citations for verification. (October 2010) |
SCART (from [Syndicat des Constructeurs d'Appareils Radiorécepteurs et Téléviseurs] Error: {{Lang}}: text has italic markup (help), Radio and Television Receiver Manufacturers' Association) is a French-originated standard and associated 21-pin connector for connecting audio-visual (AV) equipment together. It is also known as Péritel (especially in France), 21-pin EuroSCART (Sharp's marketing term for the connector in the Asian region), Euroconector[1] or EuroAV. In America, another name for SCART is EIA Multiport (an EIA interface).
In Europe, SCART is the most common method of connecting audio-visual equipment together, and has become a standard connector for such devices; it is far less common elsewhere in the world. Designed to carry analog standard-definition content, SCART is becoming obsolete with the introduction of new digital standards such as HDMI, which can carry high-definition content and multichannel audio. HDMI-CEC is derived from SCART's AV.link.
The official standard for SCART is CENELEC document number EN 50049-1. SCART is sometimes referred to as the IEC 933-1 standard.
Origins
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.[2][3]
Before SCART was introduced, consumer TV sets did not offer a standardised way of inputting signals other than RF antenna connectors, and even antenna connectors differed between countries. Assuming other connectors even existed, devices made by various 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 SO239 connector or a BNC connector.
Usage
The SCART system was intended to simplify connecting audio-video equipment (including TVs, VCRs, DVD players and game consoles). To achieve this it gathered all of the analogue signal connections into a single cable with a unique connector that 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. In addition, a TV can be awakened from standby mode or switched to video mode through a SCART connector.
Daisy chaining
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 ("up", "primary" or "1"), and another one for the set-top box or other devices ("down", "secondary" or "2"). 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.
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 "up" and "down" socket, this allows for connecting a virtually unlimited number of devices to a single SCART socket on the TV set. While audio and video signals can travel both "up" to the TV set 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 set.
"Up" and "down" are conventional. Logically the TV set is the last device of the "up" chain-path (stream) and the first device in the "down" chain path (stream). 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 set is on top and ends the "up" chain-path (stream), translating the electrical info in optic and audio. 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 set, 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 "up" or "down" chain-path (stream) may not have useful effects and may create instability.
Direct connections
As the pins for Audio and (Composite) Video use the same pins on "up" and "down" 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 "up" and "down" SCART connectors.[4] 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 only pin 7 may result in yellow images, due to the missing blue. Likewise damaging pin 11 or 15 may result in purple or blue/green images, due to the missing 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 (PB and PR) 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 (fast switching)
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 colour 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 also be driven by the use of a "transparent" colour in a teletext page.
Status and aspect ratio (slow switching)
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 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.
The same signal can be used by a 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 set than the source, so the signal usually travels "down".
SCART also 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:
- Widescreen, for televisions that are widescreen or capable of otherwise dealing with widescreen images
- Letterbox, which adds blank space (usually black) at the top and bottom of the image to give a 4:3 aspect ratio
- Pan and scan, which crops the image to achieve a 4:3 aspect ratio; only the centre portion is displayed with the 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 (e.g. the Visiopass) could not letterbox. The limitations apply mostly to satellite television receivers, while DVD players can always at least letterbox and often zoom.
Data bus
The use of the data pins was not standardised in the original SCART specification, resulting in the use of several different protocols, both proprietary protocols and semi-proprietary protocols based on standards such as D²B.
Some of the most creative usages 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 polarisers, before these became incorporated into LNBs. The daisy-chaining features were used to connect both a Pay TV decoder and a dish positioner/polariser to a single Decoder socket on the receiver.[5]
CENELEC EN 50157-1 introduced AV.link as a standardised protocol to carry advanced control information between devices. It is a single-wire serial data bus and allows carrying remote control information and to negotiate analogue signal types (e.g. RGB). AV.link is also known as nexTViewLink or under different trade names such as SmartLink, Q-Link, EasyLink, etc. It appears as the Consumer Electronics Control channel in HDMI.
Cordset types
The original SCART specification provided for different cable (cordset) types denoted by a key colour. However, colour coding is rarely used in practice and cables often use different, non-standard configurations.
| Type | Ring colour | Pins | Description | Symmetric | |
|---|---|---|---|---|---|
| U | Universal | black | 1–20, 21 | Fully wired cable. | no |
| V | Video only | white | 17–20, 21 | Only composite wires. | yes |
| C | Combined | grey | 1–4, 6, 17–20, 21 | Composite Video and Audio | yes |
| A | Audio only | yellow | 1–4, 6, 21 | Audio | yes |
| B | Bus | green | 10, 12, 21 | Only data connections | 1 |
1 depends on protocol used.
Disadvantages
|
- 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, i.e. both issue and accept composite video, and accept RGB video. In recent years, non fully wired SCART cables have tended 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 colour 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 cables are more susceptible to cross-talk, or are unable to support all communication modes. Ribbon cables may avoid mechanical tension of classic cables. Ribbon cables are perfectly suited to chain-connected stacked devices.
- 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.
Practical considerations
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.
The Nintendo GameCube†, Wii†, Dreamcast, PlayStation, PlayStation 2, PlayStation 3, Xbox and Xbox 360 can output RGB, component video, 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 Nintendo 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 video. Also, some versions of legacy consoles such as Sega's Mega Drive (Genesis) and Nintendo's SNES and Nintendo 64 (modified NTSC and early French SECAM versions only) are capable of outputting RGB signals.
^ † RGB is only available on PAL region GameCube and Wii consoles, while S-Video is only available on NTSC consoles.[6]
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 metres without amplification.[citation needed]
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.[citation needed]
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.
Using higher-quality cables such as those with ribbon cords that have properly shielded coax cables inside might help in reducing a 'ghosting' effect, but it does not always completely eliminate it due to various factors. 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 (n.b. with the recent digital switchover in the UK many newer ("digital") TVs pass their Freeview signal back to DVD recorders/VCRs to allow you to record Freeview from the AV channel that the TV is connected to without the need for an additional set top box, so if you have Sky/Virgin you can watch Sky/Virgin on AV whilst recording the Freeview channel selected on the TV's built-in digital tuner at the same time; removing this pin 19 will prevent this functionality). 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.
Blanking and switching
Two pins provide switching signals.
Pin 8, the switch signal pin, carries a DC voltage 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
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 in Europe and in specialised stores in North America.
See also
References
- ^ "Conector SCART (Euroconector)[[Category:Articles containing Spanish-language text]]". uvigo.es.
{{cite web}}: URL–wikilink conflict (help)[dead link] - ^ "La télé des années 80[[Category:Articles containing French-language text]]". croque-vacances.com.
{{cite web}}: URL–wikilink conflict (help)[dead link] - ^ "Le TI-99/4A et la Presse Informatique[[Category:Articles containing French-language text]]". perso.orange.fr/fabrice.montupet.
{{cite web}}: URL–wikilink conflict (help)[dead link] - ^ S-Video to SCART signal conversion guide.[dead link]
- ^ Based on a Pace Micro Technology Prima analog receiver manual and a DATCOM AP-500/AP-700 dish positioner manual.
- ^ http://members.optusnet.com.au/eviltim/gamescart/gamescart.htm#gamecube
External links
- Paul Gardiner, Peter Barnett, Preliminary Investigation of a SCART Lead Benchmarking Scheme
- SCART connector pinout and cables schemes
- SCART — hardwarebook.info
- RGB/VGA and SCART