Editing SCART (section)

=== 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.