Talk:Video Graphics Array/Archive 1

Archive 1

Memory base

From the article: the video memory for color mode is mapped at 0xb8000-0xbffff. I thought VGA graphics memory started at 0xa0000? At least, in linear (320x200x256) mode, where each byte was one pixel? -- pne 05:07, 26 Aug 2004 (UTC)

  Answer:  In graphics mode yes it's 0xa0000.  Colour text mode is "0xb8000".  -- Funkymonkey.

What about the VESA standard for successors to VGA?

  Feel free to add your own info :)  -- Funkymonkey.

0xb8000-0xbfff is also used for the old CGA color modes (320x200x4, 640x480x2) and text mode. Everything else (320x200x256, 640x480x16, and the EGA 16-color modes) use 0xa0000-0xaffff. 0xb0000-0xb7fff isn't usually touched by VGAs since it's the MDA text buffer. The VESA extensions to VGA are described over in Super VGA. -lee 17:17, 21 Sep 2004 (UTC)

  0xb0000-0xb7fff is a perfectly valid address space for the VGA when operating in a Mono text mode (Mode 7).  
  -- Funkymonkey

Vector Graphics Array Can anyone tell me how to connect a xbox360 console to a monitor using a VGA AV cable?What is meant by a female/female adapter?

Removed 640x400 Mode-X and Direct-X reference

I removed the reference to 800x600 and 640x400 modes, as I'm pretty sure they're not possible using standard VGA hardware. 800x600 maybe at a low refresh rate? Remember the distinction between a clone VGA and a "Super VGA" is blurred, some clone VGA's such as Oak's OTI037 256K VGA were capable of 800x600 I remember. However, this page is about the true blue IBM original. The main reason these modes should be near impossible (especially 640x400 in 256 colours) on standard VGA hardware is that the video bandwidth (28Mhz max) is too low. Horizontal Scan Rate would be unacceptably low. I'd love to be proved wrong however - if someone can demostrate the CRTC settings for a 640x400 256 colour, or 800x600 mode that would run on an IBM VGA with multisync monitor i'd be interested to see it. I also removed the reference to the 'Direct-X' term double buffering. Double Buffering has long been used as a term before the introduction of Direct-X. -- Funkymonkey May 8, 2005 - Hi Funkymonkey! There was an old MS-DOS program "FRACTINT", which claimed to support output resolutions up to 800x600 (16-color) on a true "IBM VGA adapter." Years ago, I fooled around with the program, but on an SVGA adapter, so I can't verify the program's claims. I do remember "ModeX" allowed up to 360x480 (60Hz) without resorting to outrageous refresh-rates -- a handful of MS-DOS games used this mode (my favorite was "Bananoid", a shareware clone of Arkanoid.) http://spanky.triumf.ca/www/fractint/hardware_modes.html#video_notes_anchor June 23rd, 2005. I read that link and it seems you're right about the 800x600 mode - tres cool, and a good find! We should integrate the information from that link back into the VGA page, I think i'll do that! -- Funkymonkey.

I can provide working programs that display 800x600 in 16 colors and 640x400 in 256 colors on a STOCK VGA so I know it is possible. The only drawback is that most monitors couldn't display it (it requires a very low refresh rate). If those were taken out, I'm going to put them back in. Trixter 21:38, 12 January 2006 (UTC)

Cool - I'd love to see those programs, if you can make them available. What monitors have you found are able to sync to these low refresh rates? Thanks. Funkymonkey

I'd have to find the code :-) But fractint is one of the 800x600@16 programs so just grab that and try it in DOS fullscreen. As for monitors, not many unfortunately. Trixter 23:59, 16 January 2006 (UTC)

I'm willing to accept that 800x600 is possible, and it has been show (Fractint as you say) but 640x400 in 256 colours seems unlikely due to the very low horizontal frequency that would involved. In 256 colour modes, the VGA is operating at half the horizontal clock speed as two normal clocks elapse for each pixel. Can we leave out the reference to 640x400 in 256 colours until there is some proof of it's existance? --Funkymonkey.

I guess I'm going to have to find that code then. But unless you have a low-scanning monitor (one that can do 15KHz horizontal) you probably won't get it to work. It *is* possible, I've done it, but just like 800x600x16 it displays on about 1% of monitors out there.

But what's wrong with the paragraph right under it? Does it not explain the limitations of trying to use such extreme modes? This was a big deal back then, I remember a lot of discussion around getting ColoRIX to use additional tweaked modes... Trixter 21:53, 25 January 2006 (UTC)

Leave it in if you like then, I just think it's nice if we have some evidence to backup the mode's described as possible. --Funkymonkey. The article says "360x480 (highest resolution compatible with standard VGA monitors". I guess that's for 256 color modes. What is the highest 16 color mode resolution compatible with a standard VGA monitor? Calvero2 11:32, 8 April 2007 (UTC)

VGA 256x177?

Could be possible that VGA can display 256x177? I found that when playing Rastan on Dosbox. Or pearps it's EGA tweak.

You're correct. Rastan tweaks a 256x177 mode. The 256 pixel columns across is not only easy but common; the 177 lines is the unconventional part.

256 pixel columns was a huge boon to game programmers -- it meant you could treat screen coordinates as going from 0 to 255 across, which meant your "X" variable could fit into a single byte-size register. Some games used this and put a status display up from pixel columns 256-319, but a few games, like Rastan, actually tweaked a 256-column mode. Trixter 23:10, 10 January 2006 (UTC)

Thanks. I played Rastan on my old computer with a TV plugged. The screen displays odd effects when playing Rastan.

That was CGA composite output, which displayed odd artifacts if the game didn't specifically support it. See the wikipedia article on CGA for more info. Trixter 21:39, 12 January 2006 (UTC)

My old computer does not have a CGA composite output. I used a device to connect the TV via VGA output. Peharps the device was not designed to use 256x177 mode.

It's ever worst when connecting the tv to my newest computer connected via 3d card and playing Rastan. Everything's flickering.

Meaning of VGA

It is my understanding that VGA was an important landmark in that, for the first time, standard IBM PC color computer monitors came to have the same resolution as North American TV broadcasts (NTSC standard); thence the name "Video Graphics Array", or an array of pixels matching the resolution of standard video. As written the article named "NTSC", color TV broadcasts have 486 "viewable" horizontal scanning lines per frame which closely matches VGA's 480 number. As for the 640 number it surely must match the equivalent resolution if the scanning were done with vertical lines instead of with horizontal lines, but I'm unsure about this. I don't know were to add this comment without disturbing the balance of this article. Perhaps if the original author sees this note he/she may add it appropriately.

IIRC, the 486 comes from some digital video format (DV, D1?) while broadcast NTSC has indeed 480 lines (but often more than 640 pixels per line when transmitted digitally). Christoph Päper 22:04, 1 June 2006 (UTC)

This doesn't really make much sense to me. First, the VGA was never really meant for digital video applications (among other things, it didn't have video-in/video-out capabilities). Second, VGA was not actually the first PC video system to use the 640x480 resolution; the Professional Graphics Controller before it supported 640x480, as well as several "super EGA" cards meant for use with multi-standard monitors like the NEC MultiSync II. Third, and probably most important, the VGA was the first IBM PC graphics adapter to fit into a single gate array, and at first was not offered as a separate "adapter" card. -lee 13:15, 25 September 2007 (UTC)

Original Poster: False. (1) NTSC's analog (key word) resolution is variable from 330 lines left-to-right (VHS) to 440 lines (broadcast) to 660 lines (DVD or other "lossfree" source). There's no limitation or fixed resolution, because it's an analog system. (2) VGA was hardly the first computer to feature 640x480 resolution. Several other computers already had the same capability (Commodore Amiga and Atari ST spring immediately to mind), and they were better suited to television production since they had interlace, whereas VGA used the non-compatible progressive scan. Interlace is better for 1980s TV production. (3) The earlier CGA and EGA cards had composite and S-video outputs for connections to standard televisions. As did most computers of the era, so connecting your computer to a TV was nothing new. It dated back to the 1978 Atari 800, and probably earlier than that. ---- Theaveng (talk) 15:32, 7 January 2008 (UTC)

HVGA?

Can someone familiar with this topic take a look at the recently created article on HVGA? Thanks. -- Rick Block (talk) 01:25, 8 June 2007 (UTC)

Technical details/History

AFAIK, the firt VGA appeared in the IBM Personal System/2. It was a part of the Micro Channel architecture memory controller, like modern IGP in the Northbridge. Originally, there was no such thing as "VGA Chipset" in the PS/2. The first VGA-compatible ISA chipset was a Paradise VGA (later Western Digital). - Alecv 19:24, 8 June 2007 (UTC) Answer: Shame i don't have my old PS/2 to hand, but IIRC when looking at the board you could identify discrete chips that made up the VGA. Things weren't that integrated back then. If you have ever seen an 8514/A board (i own one) it is made up of a very large number of discrete chips. It may well be that some of the core logic was integrated into the MCA memory controller, but i'm pretty sure it was a chipset all in all. (I may be talking crap though, because it depends on whether you count the video RAM, and the DAC as seperate or not) 149.254.200.220 18:02, 5 September 2007 (UTC)funkymonkey

The VGA itself was indeed a separate chip, IBM part number 15F6864. A complete VGA setup included the '6864, 8 NEC 4464 RAM chips (64kx4, a total of 256k), an Inmos G171 6-bit/3-channel RAMDAC with 256-entry CLUT, and two dot clock crystals (25.175 MHz and 28.322 MHz). Pretty much everyone used this same layout, which made upgrading things piece-by-piece easy (adding more RAM and higher dot clocks were some of the first mods people did to the basic design). The early Paradise chips were very similar to the 15F6864, even to the point of using external clock crystals (I saw a Paradise board with 5 of them once, sometime in the mid-1990s...yeah, it was old even then).

While I'm thinking about it: The MCGA, VGA's short-lived, cut-down sibling, was embedded somewhere in the chipset of the PS/2 Models 25/30-8086, and at least two of those chips were semi-custom Epson gate arrays. -lee 18:22, 24 September 2007 (UTC)

Lee that is awesome information, very impressed. How did you come by that info? -FunkyMonkey

Partially from trolling the web to refresh my memory, partially from having a basement full of old PCs (including an IBM PS/2 Model 80 at one point) and tons and tons of old ISA video cards. From about 1993-2000, my brother was friends with a second-hand store owner who frequented Government surplus auctions, and he would just give us stuff (most of it dating from the late 1980s and very early 1990s). We ended up having to trash most of it when we moved house in 2000, though. -lee (talk) 16:26, 10 June 2008 (UTC)

funkymonkey, could you please take a picture of your 8514/A board? The 8514 article is pretty sparse at the moment, and it's kind of become a pet project of mine because of a game called Mah Jongg -8514- that made a bad bet on the 8514 standard becoming widely adopted. DOSGuy 21:21, 24 September 2007 (UTC)

Only just saw this, but yes, I'd be happy to post a pic on the 8514 article (might need a dust off first!!). The girlfriend is coming over tonight, so I'll ask her to bring the camera over. I'll also post you a URL to a website with all the pics here once done. -FunkyMonkey

The default palette?

From experimentation, I don't believe that the mode 13h palette is the graphics adapter's default palette. By setting the graphics mode directly, I found 8 shades of the EGA colouring scheme, and 192 blank colours. Though I did this under QEMU, so it might not be right, however, the so-called "default palette" is almost definitely stored in the BIOS. I'll try on actual hardware (no original VGA chipset though :\) --thematrixeatsyou 08:49, 2 November 2007 (UTC)

I'm not sure what you are trying to say here, but mode 13h is not a palette. VGA has a default palette defined that is EGA and CGA compatible, but applications are free to reprogram that palette as they see fit. It is likely that the default palette is stored in the BIOS or Video BIOS, but that is just an implementation detail.

--Anss123 09:18, 2 November 2007 (UTC)