VGATV Version 2.0By Paulo Sergio Coelho, 1997
This program allows you to use your TV as a monitor, given that you use the proper hardware to connect your VGA to the output equipment.
The driver is a TSR (Terminate and Stay Resident) which will try to make sure your VGA card is, at all times, properly programmed for TV timings, which are quite different from VGA standards:
- VGA timings are normally 31.469KHz horizontal frequency, and 70.08Hz vertical frequency. Non-interlaced.
- PAL and NTSC are interlaced. PAL (Phase Alternating Line) has a horizontal frequency of 15.625Khz and 50Hz vertical frequency. NTSC (National Television Standards Committee) has 15.750Khz and 60Hz respectively.
For this to work, you need the following:
- a) a IBM PC or compatible computer system (clone for short :-). And yes, your 4.77Mhz IBM PC will do;
- b) a VGA card;
- c) some memory to load this driver
- d) some hardware for the video connection, described below, without which, this whole thing just becomes an academic exercise...;
- e) a BIG screen TV, for those games;
- f) a VCR for saving those presentations;
- g) a sound board connected to your Hi-Fi system, with volume turned fully clockwise, or at the point where neighbours start to complain :-)
- h) some application software (a game _IS_ an application!).
Humm, right. As stated above, besides the occasional badly-behaved program, this driver comes with guaranteed limitations:
With PAL timings, only resolutions up to 800x600 can be fully viewed. With NTSC this figure goes down to 640x480, thanks to the lower resolution of this TV standard (525 horizontal lines, as opposed to PAL's 625). Note that these resolutions are available in ALL VGA cards.
Since there are obvious limitations on the number of lines, modes that have more than 525/625 lines, use the trick described below, in which the resolution is actually halved, though for most purposes, it doesn't show much. Only if you're trying to display text, you might run into trouble if the pitch is too small. However, for photographs or most drawings, there isn't a noticeable decrease in resolution.
In order to get the correct aspect ratio of the screen modes, the maximum resolution in PAL is 1600x1280 and in NTSC 1280x1024. Resolution is halved in modes 1024x768 and above, in both PAL and NTSC, but NTSC has much more overscan than PAL. Resolution is also halved in unsupported chipsets at 640x480 and above resolutions, if they aren't interlaced originally.
Because standard VGA has no support for interlaced screen modes, a trick has to be employed to get the visible area of a video mode in the screen at all times. This, however, implies that every other line in the screen will be missing, namely, the odd numbered lines (1,3,5,...). While this doesn't affect images and drawings much, text is a pain to read. Fortunately, your VGA card's chipset may be supported by the program, thus allowing you to have an interlaced screen and no missing lines.
Also, the program is clever enough to, under certain conditions, support non-standard VGA modes while not supporting any specific chipset. This depends on the fact that some modes on some boards, specifically turn on interlacing so that the driver doesn't have to do it, and you can see a 1280x1024 mode even if the driver doesn't actually support your board. If the mode has more than 600 lines, and doesn't turn on interlacing, only part of the screen will be shown, full-screen, but stretched downwards. Also, depending on how the program sets the dot-clock, some modes might not sync, while others, higher resolution ones, might do. 800x600 is a general culprit...
There is no limit about colours, though some boards, due to the way they program the card, might not allow us to see 640x480 at 16.7Mcolours, or more than 800x600 at 64K/32K colours. Others do, however!
Note that screen modes which have less than 300 lines, don't need interlacing, thus are fully viewable, with no lines missing. This includes all low resolution modes, such as mode 13h (320x200 with 256 colours).
Text modes are limited to 32 lines, but there is no limitation on width. Currently, modes 40x25, 80x25 and 132x25 are supported since I know of none other. If they appear, there might be a chance that the program does recognize them. Modes with more than 25 (or 30, if your card has 30-line modes) won't show more than 32 lines at one time. The remaining lines aren't shown.
Also, some programs reprogram text mode fonts (namely those from PC Tools, Norton Utilities, and others), which may have nasty effects when you get back to DOS. If the screen is corrupted on exit, try resetting the screen by pressing Ctrl+Alt+R.
200-line modes are not interlaced. I tried to, but it seemed impossible, at least on the Oak 087 chipset. Anyway, as it is, the screen is much stabler, since there is no interlacing.
First, there's the the original VGA->SCART project, by Tomi Engdahl. This circuit is in HTML format, in http://www.epanorama.net/counter.php?url=http://www.hut.fi/~then/circuits/vga2tv.html, which contains help, hints, schematics (proper drawings), even a picture of one PCB, plus drivers. My ASCII version wouldn't make justice to the schema- tics on that page, so you'll have to check there for them. I'll have enough trouble to place my own circuit design here...
Anyway, about the SCART version. SCART has an RGB input, therefore it's much better than the composite video version. Remember however, that what you see on your everyday TV broadcast, is truly composite video, so it's not that bad. Except RGB is even better. However, composite has other advantages, such as:
- you can record the signals on tape, since it seems some (all?) VCRs don't have RGB inputs on the SCART connection;
- here are lots of SCARTs around, but on older equipment, you'll get plain RCA composite video plugs, so the SCART wouldn't work; and,
- SCART is just too big, and it's not too healthy to get it in and out the input equipment at all times, unless it's a thing to plug and forget.
On my circuit, I used a simplified version of Tomi Engdahl's VGA->SCART circuit, to get composite sync, so, some credit must go to him. I also based the design heavily on Motorola's MC1377 datasheet, using more or less the same components, with mostly the same values. You should see this datasheet if in doubt. Check out http://www.epanorama.net/counter.php?url=http://motserv.indirect.com/cgi-bin/dlsrch, and follow on-screen instructions.
You can (and probably should) build an RGB circuit around another chip. I know of 2: Analog Devices AD722/AD724, which is a chip as simple as it gets, allowing S-VHS output, easily (unlike the MC1377, which requires yet more circuitry for this), and Sony's CXA1645, which is a bit more complicated than the AD722/AD724, but has RGB passthrough, allowing RGB signals to feed the chip and go on to something else in the board (like a SCART output).
The circuit is comprised of 3 parts: the circuit box itself, a cable going to the outside the case plugged into the VGA output, and another cable which goes from the circuit box to the input equipment. This cable also plugs on the circuit box (and is not soldered to the circuit's PCB as the other cable). You can, of course, do it your own way.
Outside component list:
1 DB15P male VGA plug 1 multi-wire cable (I used 8 wires+shield) to connect the VGA to the circuit box. 1 box (metalic is better, though a plastic one is cheaper, and it's the one I also used). This holds the circuit. The box is 13cm x 5.5cm x 2.5 cm (W x D x H). 1 female panel-mountable RCA plug 1 male PCB mountable DC socket 2 male RCA plugs (for the connecting cable) 1 75� cable, to connect the box to the input equipment. You can probably get one of these in a shop somewhere. In that case, disregard the 2 male RCAs above. I used a 50� cable (by mistake), but it's quite okay. Just don't use plain audio cable for this. It's AWFUL... 1 12VDC power supply. The circuit I made is only regulated for 5V. The chip itself (MC1377) has an internal 8.5V regulator. Thus, you can plug in from about 10V to 14V, unregulated power supply. This means a 9VDC transformer can be used. I do. The chip needs 60mA maximum, but I haven't determined the entire circuit supply current needs.
The inside component list is comprised of:
1 Motorola MC1377P chip 1 DIP-20 socket, for the chip 1 7805 5V PS regulator 2 BC547 transistors 1 Philips 330ns delay-line. These are H-A-R-D to find. Motorola suggests a 400ns delay line, though it seems 330ns are more common here in Europe. Best place to look for one of these things, is inside a TV. The Philips one is green, and about the size of your thumb (1 inch). I have seen 3 so far, including the one I have. I have seen 2 other, being used in 2 Elektor Magazine projects. You can try your local TV repair shop. Beware that some folks don't even know what this is, so be patient... The impedance on these delay lines is 1K�. Motorola advises that it falls between 1K� and 1.5K�. 1 chroma bandpass transformer. This one's a little hard to tell what it is. If you don't know diddley about this, it's one of those things inside the TV that you turn round and around, which have a lot of wires around them. About 1 cm high. For details on skiping this, refer to the MC1377P datasheet. But you can probably get one of your electronics-skilled friends to built one for you. Here's the details. The transformer itself is 15mm high, plus 3.5mm for the pins, which are 0.7mm in diameter. Has 2 windings, and each one takes 60 turns of #38 AWG wire (0.1 m/m). Unloaded Q (Pins 1-3): 15 @ 2.5Mhz. Inductance: 30�H � 10% @ 2.5Mhz. Bottom view: ___________ / \ � 3 -\ /-4 � -------- � / \ � ^ � 2 \ S / S � 7 � 0.2mm � / / � v � 1 - \- 5 � -------- \___________/ 1 4.43Mhz crystal, just like the ones found on TVs. 4.43Mhz is the PAL color carrier frequency. NTSC is 3.58Mhz, so you should get the appropriate one for you. Resistors: 1 trimmer, 47Kohm 4 75ohm 3 47ohm 3 1.8Kohm 1 2.7Kohm 1 33Kohm 1 3.3Kohm 2 1Kohm 1 220ohm Capacitors: 1 trimmer 5pF-25pF (doesn't matter much, get one around this) 1 100uF, 16V (or more V) 1 10uF, 25V 4 100nF 1 12pF 2 1nF 2 10nF 2 180pF 1 33pF (NTSC: 47pF) 1 62pF (NTSC:100pF) 3 22uFNow, follows 3 parts of the circuit, which should be joined together in the end.
If you want to share some comments on this, suggestions, criticism, chipset programming details on unsupported cards, post-cards, money, etc, just write to:
e-mail : firstname.lastname@example.org
snail-mail : Paulo Srgio Coelho Rua Luis de Cames, 25 Pateiro 8400 Lagoa PortugalPlease note that mail-bombs will be returned to sender. No kidding.
The legal juice
Ok, so you find this little piece of software useful.
Very well, you can use it, at your OWN risk, meaning if you blow up the TV, the VCR or your room, I really don't give a damn, it was YOUR fault, NOT mine. Same thing for the hardware description. So there.
Also, this software may be copied, used and abused, but nowhere modified. This includes not only the executable, but also this DOC file, which should always be present with the executable.
Additionally, you can consider this work, one of the following:
- freeware, meaning you can use it 'till it wears off;
- hareware, meaning if you send me money, I'll appreciate it, and you'll win a line in this DOC; or,
- cardware, in which you send me one (or more!) of those fancy postcards showing off the views on your local town.
All right, here's a bunch of thanks for the folks which have a piece in this.
- Me - for typing this thing in, and generally spending lots of hours in front of a TV making this sh*t work;
- You - for being so patient, that you've actually read this thing so far;
- Tomi Engdahl (email@example.com) - for developing the initial VGA->SCART hardware design, and having such a nice, informative page on the net, all about this VGA to TV stuff. Also, thanks for the help provided, in the countless mails about hardware, and other technical issues;
- Rui "Gusmäo" Rodrigues (firstname.lastname@example.org, CT1FKP) - He actually built my RGB-composite video circuit, after my design. He also has put a lot with me, since I'm such a no-good with the soldering iron, and an almost illiterate when it comes to electronics...;
- Herman Dullink (email@example.com) - for helping out on VESA issues (lots of info), S3 and Tseng Labs chipsets, interlace programming details on these, and mode X programming;
- Avery Lee (Psilon@concentric.net) - for helping out a bit on mode X, comments on an initial test program, info on how to turn protection off in the S3 chipset, and testing this in a Genoa Phantom 64;
Thanks to you all!