Comments on drivers for VGA to TV adapter
First I tried to write my own drivers, but I found out that this was not easy. The problems is that when something goes wrong (no picture on TV), you need a multimeterm oscilloscope, frequency counter to find out what is wrong. VGA chips are not very easy to program and there are many annoying features in it. I wrote some test programs for few VGA modes and managed to get text mode to show in TV screen. You can download my test program which runs under MS-DOS or you can look at the source code to get the idea what needs to be done to show VGA pictures on TV screen.
When I browsed through many FTP sites for looking drivers for my SVGA card, I found a driver for Cirrus 542x based SVGA cards to show NTSC modes. That driver supports standard VGA modes and also some of the superVGA modes. The disadvantage of this driver is that it works only with Cirrus 542x chipsets.
I searched different WWW-pages and finally I found that Boffin Multimedia Systems used similar approaches in their now discontinued VIP50 VGA to TV (NTSC) converter. I tested their drivers and they seem to work very fine with my circuit also. That driver support standard VGA modes with standard VGA card and has some nice features like picture position adjusting. The driver has also support for 640x480 256 color mode with Trident, Tseng and OAK chipset. For more information, check the documentation in the driver package.
I also found that Advanced Digital Systems also makes inexpensive VGA to TV (NTSC) converters. I checked their GAME ZAPPER product specifications (the product seems to be now discontinued). They seemed to also use software drivers and simple hardware. I downloaded their drivers and tested. Again I got the drivers working nicely with my adapter.
TelevEyes VGA-to-TV converter drivers have been reported to be quite well working drivers which work nicely with many DOS games including Doom, Heretic, Descent and many other titles which use DOS4GW dos extender.
For those who would like to get 50 Hz picture out of VGA card instead of 60 Hz picture (as provided by those drivers above), I have develloped some simple utilitity programs for changing the frame rate to 50 Hz.
There has become available another VGA to SCART design the net lately. It is designed by Dario Armel and it is available at http://www.epanorama.net/counter.php?url=http://www.platino.it/guests/dario/vga.htm. The text is in Italian, but the circuit itself should be easy to understand without the text. The design looks quite the same that I used in one of my prototypes. There are also available DOS drivers for this circuit and those drivers should work well also with my circuit.
I have also written my own drivers for VGA to PAL and NTSC TV conversion. Version 0.6 is already available here and more is coming when I have enough free time to make them working. This driver supports VGA all standard VGA modes. Because the driver supports almost any standard VGA mode, you can easily use with nearly any normal DOS application which does not do any serious VGA card tweaking. Because the driver also supports text mode and other graphics modes, you can very well use it with many games (DOOM etc.) and appliaction programs. My own driver programs seem to have some problem with certain graphics card chipsets (mostly S3 based chipsets).
If you have external RGB to PAL composite video converter, you can use this driver to record any 320x200 up to 256 color graphics to your VCR. This makes for example possible to record 320x200 FLIC aminations to VCR. I have tested my driver with PLAYFLC playser coming with VistaPro 3.0 software, which is a commercial landscape rendering software from Virtual Laboratories, Inc.
Tomi Engdahl <Tomi.Engdahl@iki.fi>