General information about VGA to TV drivers
The VGA to TV circuit needs a driver to operate correctly. Without suitable driver it is not possible to get any picture to TV screen. The driver does the job to adapt the VGA card to operate at TV scan frequencies.
Most of the drivers enable using standard VGA modes on TV with well-behaving DOS programs. Those drivers work nicely with nearly every VGA card and every standard VGA mode (except S3 based cards). The standard VGA modes can be quite easily supported in wide variety of PC graphics cards because VGA is a standard display technology for PCs. VGA interface relies on register-based interface that is increasingly emulated by higher-level graphics accelerators. The quality of emulation varies from card to card but is very ralely 100% despite of claims made my graphics card and chipset manufacturers. If every card would be 100% compatible with original VGA card the basic VGA drivers would work in every PC graphics card with VGA emulation. Because standard VGA hardware does not support interlaced display output then card specific drivers are needed to support higher VGA resolution (more than 240 vertical lines) graphics modes well. SuperVGA modes are more problematic because their implementation is graphics card chipset specific and are supported only in limited selection of SVGA cards. For more details on the driver implementation and resons why some modes are not supported can be found from my How I do the conversion document.
The driver situation for Windows is worse. Some drivers support Windows operation in standard VGA mode (640x480 resolution with 16 colors). Windows can be succesfully used in TV screen only with a limited selection of VGA cards. The maximum resolution you can ever use in Windows with TV is 640x480 in NTSC TVs and 800x600 in PAL TVs.
Linux Xfree86 users don't need any special drivers. When the user spcifies suitable parameters for TV operation in Linux Xfree86 configuration file and the card can accept them the TV operation is possible.
Tomi Engdahl <[email protected]>