TV Output for PC 97

This section summarizes the key design issues and requirements for TV output capabilities, which are recommended for all system types and required for any Entertainment PC 97 PC system that does not include a large-screen entertainment monitor.

The requirements in this section apply only if the capability is present on a PC system or on a graphics adapter that supports TV output capabilities. Some TV output capabilities listed in this section are required only for Entertainment PC 97.

The required support allows an NTSC/PAL TV to be used as a primary or secondary display surface for the Windows operating system and Windows-based applications. Such a display surface allows more realistic game, video, and multimedia experiences for users who want to use the large-screen TV they might already own.

If TV output capabilities are provided in a PC system, support is required for either NTSC or PAL TV output standards:

• NTSC (National Television System Committee) refers to the TV standards originally formulated in the United States. Countries using NTSC standards include Canada, Japan, and Mexico.
• PAL (Phase-Alternation Line) refers to a TV system first developed in Germany. Countries using PAL standards include Austria, Belgium Brazil, Denmark, Finland, the Netherlands, Norway, Sweden, Switzerland, and the U.K.

For information about world TV standards, see:

http://www.bbc.co.uk/aberdeen/eng_info/world_tv.htm

34. Support both NTSC and PAL output

Either NTSC or PAL standards must be supported if TV output capabilities are included in the adapter or system design; however, it is recommended to support both standards. If NTSC is supported, the NTSC system must support 640x400 and 640x480 at 60 Hz. If PAL is supported, the PAL system must support 640x480 and 800x600 at 50 Hz. Whether either or both output standards are supported, software must have the capability to enable and disable TV and VGA output independently.

Note For NTSC, 60-Hz mode described in this section is actually 59.940 Hz.

35. Default boot mode supports appropriate locale

TV output must work automatically as the primary display if a VGA monitor is not attached. The graphics adapter must default to modes compatible with TV output. Adapters manufactured for NTSC countries should default to 60-Hz modes; those manufactured for PAL countries should default to 50-Hz modes.

36. Underscan scaling

The TV-output adapter must be able to correct horizontal and vertical overscan using hardware scaling. This allows 640x480 resolution modes to fit onto NTSC displays and 800x600 modes to fit onto PAL displays. Driver software must have the capability to enable and disable scaling and also adjust scaling for compatibility with a variety of TVs. When TVs age, overscan reduces, so less scaling is required. Also, overscan can be enabled by software when the PC is playing full-screen video.

37. Flicker filter

The TV-output adapter must use multi-line (three-tap minimum) hardware filtering techniques for flicker reduction. Enable, disable, and adjust capabilities for the flicker filter must be able to be controlled by software. Also, overscan can be enabled by software when the PC is playing full-screen video.

Note Flicker filter is not required in overscan mode.

38. Proper termination

Proper termination is required so that optimal picture quality from any connector does not require displays to be attached to other connectors. For example, a VGA monitor must not be required for the S-Video output to appear properly.

39. Support RCA-style composite video and S-Video connectors

S-Video dramatically improves the picture quality of the NTSC/PAL scan converter, compared to composite video. This standard is designed to reduce crosstalk between chrominance and luminance signals and to increase the luminance bandwidth capability of the TV. For a description of this standard, see:

http://www.bbc.co.uk/aberdeen/eng_info/s-video.htm

Notice that most European TV sets now have two SCART sockets (also called Peritel); one allows stereo audio and composite video input/output switchable to RGB inputs; the other supports switching from composite input to S-Video input. The first can be used to connect a satellite receiver for RGB capability; the second can be used to connect a VCR using S-Video for TV output. A camcorder usually has connections for composite video, stereo audio, and S-Video. For a description of the SCART standard, see:

http://www.bbc.co.uk/aberdeen/eng_info/scart.htm

40. Support both VGA and TV output

In addition to TV output, the system must also support VGA output to ensure that users with existing larger-screen VGA monitors can use this output capability.

Note Simultaneous output to VGA monitor and TV is recommended, but not required.

41. Positioning

Software must be able to program the TV-output hardware to position the TV image in increments of four pixels horizontally and four scan lines vertically.

42. Software detection of TV connection

Software must be able to read the TV output hardware to detect whether a TV is attached to either S-Video or composite output connectors. (Detection of a VGA monitor is achieved using the separate DDC requirement for graphics adapters and monitors.) This is required to allow the operating system and graphics drivers to support display output correctly during the startup sequence (for example, determining what resolution and refresh rate to use), and for applications to adjust their user interfaces appropriately to the screen capabilities.