Technology Trade-offs
Using analog R′G′B′ or YPbPr video eliminates NTSC/PAL encoding and decoding artifacts. As a result, the picture is sharper and has less noise. More color bandwidth is also available, increasing the horizontal detail.
S-Video Interface
The RCA phono connector (consumer market) or BNC connector (pro-video market) transfers a composite NTSC or PAL video signal, made by adding the intensity (Y) and color (C) video signals together. The television then has to separate these Y and C video signals in order to display the picture. The problem is that the Y/C separation process is never perfect.
Many video components now support a 4-pin “S1” S-video connector, illustrated in Figure 4.1 (the female connector viewpoint). This connector keeps the intensity (Y) and color (C) video signals separate, eliminating the Y/C separation process in the TV. As a result, the picture is sharper and has less noise.
Figure 4.1. S-Video Connector and Signal Names.
NTSC and PAL VBI (vertical blanking interval) data may be present on the 480i or 576i Y video signal.
The “S2” version adds a +5 V DC offset to the C signal when a widescreen (16:9) anamorphic program (horizontally squeezed by 25%) is present. A 16:9 TV detects the DC offset and horizontally expands the 4:3 image to fill the screen, restoring the correct aspect ratio of the program. The “S3” version also supports using a +2.3 V offset when a program is letterboxed.
The IEC 60933-5 standard specifies the S-video connector, including signal levels.
Insider Info
The PC market also uses an extended S-Video interface. This interface has 7 pins, as shown in Figure 4.1, and is backwards compatible with the 4-pin interface. The use of the three additional pins varies by manufacturer. They may be used to support an I2C interface (SDA bidirectional data pin and SCL clock pin), +12V power, a composite NTSC/PAL video signal (CVBS), or analog R′G′B′ or YPbPr video signals.
SCART Interface
Most consumer video components in Europe support one or two 21-pin SCART connectors (also known as Peritel, Peritelevision, and Euroconnector). This connection allows analog R′G′B′ video or S-video, composite video, and analog stereo audio to be transmitted between equipment using a single cable. The composite video signal must always be present, as it provides the basic video timing for the analog R′G′B′ video signals. Note that the 700 mV R′G′B′ signals do not have a blanking pedestal or sync information, as illustrated in Figure 4.4.
PAL VBI (vertical blanking interval) data may be present on the 576i composite video signal.
There are now several types of SCART pinouts, depending on the specific functions implemented, as shown in Table 4.1. Pinout details are shown in Figure 4.2.
Table 4.1. SCART Connector Signals
| Pin | Function | Signal Level | Impedance |
|---|---|---|---|
| 1 | right audio out | 0.5V rms | <1K ohm |
| 2 | right audio in | 0.5V rms | >10K ohm |
| 3 | left/mono audio out | 0.5V rms | <1K ohm |
| 4 | ground - for pins 1, 2, 3, 6 | ||
| 5 | ground - for pin 7 | ||
| 6 | left/mono audio in | 0.5V rms | >10K ohm |
| 7 | blue (or C) video in/out | 0.7V (or 0.3V burst) | 75 ohms |
| 8 | status and aspect ratio in/out | 9.5V–12V=4:3 source | >10K ohm |
| 4.5V–7V=16:9 source | |||
| 0V–2V=inactive source | |||
| 9 | ground - for pin 11 | ||
| 10 | data 2 | ||
| 11 | green video in/out | 0.7V | 75 ohms |
| 12 | data 1 | ||
| 13 | ground - for pin 15 | ||
| 14 | ground - for pin 16 | ||
| 15 | red (or C) video in/out | 0.7V (or 0.3V burst) | 75 ohms |
| 16 | RGB control in/out | 1–3V=RGB, 0–0.4V=composite | 75 ohms |
| 17 | ground - for pin 19 | ||
| 18 | ground - for pin 20 | ||
| 19 | composite (or Y) video out | 1V | 75 ohms |
| 20 | composite (or Y) video in | 1V | 75 ohms |
| 21 | ground – for pins 8, 10, 12, shield |
Note: Often, the SCART 1 connector supports composite video and RGB, the SCART 2 connector supports composite video and S-Video, and the SCART 3 connector supports only composite video. SCART connections may also be used to add external decoders or descramblers to the video path, the video signal goes out and comes back in.
The RGB control signal controls the TV switch between the composite and RGB inputs, enabling the overlaying of text onto the video, even the internal TV program. This enables an external teletext or closed captioning decoder to add information over the current program. If pin 16 is held high, signifying RGB signals are present, the sync is still carried on the Composite Video pin. Some devices (such as DVD players) may provide RGB on a SCART and hold pin 16 permanently high.
When a source becomes active, it sets a 12V level on pin 8. This causes the TV to automatically switch to that SCART input. When the source stops, the signal returns to 0 V and TV viewing is resumed. If an anamorphic 16:9 program is present, the source raises the signal on pin 8 to only 6 V. This causes the TV to switch to that SCART input and at the same time enable the video processing for anamorphic 16:9 programs.
Figure 4.2. SCART Connector.
The CENELEC EN 50049–1 and IEC 60933 standards specify the basic SCART connector, including signal levels.