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Tandy 12" Monochrome VGA, AKA 'Paper White VGA'

S

Stone

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It's a Tandy, Model VM-1, 12" monochrome VGA. It displays 256 shades of gray instead of colors. It's got a sharp, clear picture. This model was an option for the TRS-80 Model 2000, Tandy 3000, or Tandy 3000 HL. It doesn't need to be attached to a Tandy, though... just a VGA card. The pic I took (below) of this was on my XT with a 16-bit 512k Trident video card.

P2140091a.jpg
 
Actually, VGA monochrome can only display 64 shades of gray, because it only uses the green pin for the video signal, whereas a color VGA monitor uses the red, green, and blue pins, giving a total palette of 64 x 64 x 64 = 262,144 possible colors.

Nonetheless, 64 shades of gray is certainly more than adequate, and VGA monochrome monitors tend to have a very nice easy-on-the-eyes display. They're smaller and lighter than color monitors, too, making them great for use as a test bench monitor.
 
vwestlife said:
Actually, VGA monochrome can only display 64 shades of gray, because it only uses the green pin for the video signal, whereas a color VGA monitor uses the red, green, and blue pins, giving a total palette of 64 x 64 x 64 = 262,144 possible colors.
Click to expand...
I'm going to disagree. Why? Because I have the paper white in front of me and I just counted the colors/shades. I know that on pic I posted above it's impossible to discern everything but on the monitor itself it's quite possible. It gave me a headache, though. :) I got 253 one time and 255 the other. Statistically, that says it does 256, not 64. If you just look at the pic above you'll see that there's three VGA bars, high, medium and low intensity. On those bars alone I counted between 221 and 223 shades.
 
Stone said:
I'm going to disagree. Why? Because I have the paper white in front of me and I just counted the colors/shades. I know that on pic I posted above it's impossible to discern everything but on the monitor itself it's quite possible. It gave me a headache, though. :) I got 253 one time and 255 the other. Statistically, that says it does 256, not 64. If you just look at the pic above you'll see that there's three VGA bars, high, medium and low intensity. On those bars alone I counted between 221 and 223 shades.
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Were you using 24-bit "true color" mode on a Super VGA card? That is the only way to get ~256 shades of gray, because 24-bit color uses 256 R x 256 G x 256 B to get 16.7 million colors. The monochrome monitor only uses the green pin, so it sees a theoretical maximum of 256 shades of gray in 24-bit mode. But with standard VGA, only 64 shades are possible.
 
vwestlife said:
Actually, VGA monochrome can only display 64 shades of gray, because it only uses the green pin for the video signal, whereas a color VGA monitor uses the red, green, and blue pins, giving a total palette of 64 x 64 x 64 = 262,144 possible colors.

Nonetheless, 64 shades of gray is certainly more than adequate, and VGA monochrome monitors tend to have a very nice easy-on-the-eyes display. They're smaller and lighter than color monitors, too, making them great for use as a test bench monitor.
Click to expand...

Are you sure that's true? It would seem to me that would make the monitor completely "blind" to red and blue colors, and things would render very strangely on the display if that were the case.
 
geoffm3 said:
Are you sure that's true? It would seem to me that would make the monitor completely "blind" to red and blue colors, and things would render very strangely on the display if that were the case.
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What you say would certainly seem to make sense if it weren't for the fact that there are no red or blue pins in the cable. The six pins in the mono VGA cable are, 2, 5, 7, 12, 13, and 14. Red and blue are 1 and 3 and they're not there. Confusing, isn't it?
 
geoffm3 said:
Are you sure that's true? It would seem to me that would make the monitor completely "blind" to red and blue colors, and things would render very strangely on the display if that were the case.
Click to expand...

At least with true-blue IBM monochrome VGA monitors, the monitor has a "sense pin" to tell the VGA card to switch into monochrome mode, in which case all of the video information is sent through the "green" pin.

Some info a quick search dug up:
Compaq (and perhaps some other companies) use the "Sense" lines as a way of telling what kind of monitor is connected. Newer monitors with DDC (also called Plug-n-play) use some of these pins.

[From: Ashok Cates (acates@clark.net)]

The ID bit pins in the 15 pin connector are shorted/left open to identify the type of monitor. I don't think they are very important anymore, as most cards have software to set resolutions, refresh rates etc. However, I think their functions are:

ID bit 0 and ID bit 2 grounded:
Dual frequency analog color interlaced (8514 or compatible) or variable frequency analog color interlaced.

ID bit 0 grounded, ID bit 2 not connected:
Fixed frequency analog color (8512, 8513, or compatible) or variable frequency analog color non-interlaced.

ID bit 0 not connected, ID bit 2 grounded:
Fixed frequency analog monochrome (8503 or compatible) or variable frequency analog monochrome.

-ID bit 1 and ID bit 2 are usually connected together. -Monitor model numbers are for IBM monitors.
Click to expand...
 
vwestlife said:
At least with true-blue IBM monochrome VGA monitors, the monitor has a "sense pin" to tell the VGA card to switch into monochrome mode, in which case all of the video information is sent through the "green" pin.

Compaq (and perhaps some other companies) use the "Sense" lines as a way of telling what kind of monitor is connected. Newer monitors with DDC (also called Plug-n-play) use some of these pins.
Click to expand...
Pin 12 is DDC and this monitor has pin 12.
 
I used to have a couple of VGA mono monitors in use here (I think they were Tatungs) but gave up after awhile. While they were lots cheaper than a color model, the attempt to render colors into grayscale left me squinting to figure out what was on the screen. That's probably why they were never popular.
 
Stone said:
Pin 12 is DDC and this monitor has pin 12.
Click to expand...

The old monochrome sense pin was reused for DDC. Modern VGA cards/drivers usually don't work well with the old mono monitors for exactly that reason, IE, they don't recognize the old-fashioned way of signalling mono-only and they go ahead and send a color signal to it, which means that 2/3rds of the picture information is lost. Solid red/green areas will simply be black and shades incorporating those colors will be way off. This was a problem even back in the "old days" with some software that directly programmed the VGA card and ignored the distinction. (The sense line was a "serving suggestion" to use an alternate palette, not a hardware crossover/mixer switch.) The early Xfree86 VGA drivers for Linux were severe offenders there.

Anyway, I went through several cheap mono monitors back then and never had much luck with them. They always seemed to be "flaky", at least compared to mono Hercules units. (Perhaps the analog signaling was more prone to noise than the digital standards, but was less obvious on a cheapo color monitor where said flakiness was spread over three guns.)

As to "seeing" 256 shades of gray instead of 64, I dunno... placebo effect? (Edit: Or, are you looking at "color bars"? If that's the case the same gray is probably in there multiple times with the multiple occurrences non-adjacent to each other.)
 
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Eudimorphodon said:
As to "seeing" 256 shades of gray instead of 64, I dunno... placebo effect? (Edit: Or, are you looking at "color bars"? If that's the case the same gray is probably in there multiple times with the multiple occurrences non-adjacent to each other.)
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When you say 'probably' you indicate some degree of speculation on your part. Am I incorrect or do you know this to be factual? I don't know if the information on the following links is factual or just an advertising claim as I haven't been able to find any manufacturers' specs on any of these monitors.

http://www.frynge.com/monitors2.htm

http://www.frynge.com/monitors.htm
 
Stone said:
When you say 'probably' you indicate some degree of speculation on your part. Am I incorrect or do you know this to be factual?
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Technically an analog VGA monitor is capable of an infinite range of grayscales, since the brightness of a spot on the screen is determined directly by the voltage level present on the input line, ranging from zero to whatever the maximum is. (don't recall off the top of my head.) "256 colors" assumes an 8-bit-per-channel DAC, which has been pretty standard since around, what, 1990? There are video cards with 30 bit or even 36-bit (10 or 12 bits per channel) DACs, connect your monitor to one of them and you'll get 1024 or 4096 grays respectively. I don't know what the resolution of the DACs used on, for instance, Macintosh computers typically were but several models going back to the LC era supported VGA-frequency monitors. Perhaps that's a possible source of the "256" number.

HOWEVER, the original VGA specification has a 6 bit-per-channel/18 bit DAC, which translates to a maximum of 64 levels of intensity if you're using one channel, which a VGA mono monitor does. Didn't make this up, it's copiously documented on the web. Google "IBM VGA shades of gray" and one of the top hits is a link to an InfoWorld article from 1987 on Google Books which relates "If you need monochrome and have software that will support VGA, you will delight in monochrome VGA's capability to produce continuous monochrome tones in 64 shades of gray". (I also recall "64" being the quoted number in IBM's sales literature, etc, etc.) See also the documentation for the "palette" command in QuickBasic, which I believe was the first BASIC to support VGA. (Was there ever a version of BASICA/GWBASIC that went beyond EGA?) It quite clearly notes that valid palette values range from 0 to 63.

Really, it's a pointless argument, but *strictly speaking* if a VGA Mono monitor is connected to a "classic" VGA card lacking a TrueColor DAC it's limited to 64 grays, no matter what the sales literature says. It's not a swipe against what you're selling, it's just how it is.

(EDIT: Believe it or not, a related limitation is still around today. Many cheaper LCD panels used in both laptops and stand-alone monitors are equipped with 18 bit digital interfaces. Those LCDs *cannot* display more than 64 shades of true gray. See this link:

http://arstechnica.com/apple/news/2007/05/lawsuit-over-mac-book-mac-book-pro-displays.ars

There are image files floating around out there which are designed explicitly to reveal what the color depth of your LCD truly is, and they involve counting greyscale levels.)
 
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I don't know a thing about EE. But I remember in about 1990 when I was handling these mono VGAs by the boatload. And they were all the '256 shades of gray' types. Didn't you run into those 20 or so years ago?
 
My problem with the mono VGA monitors was that colors that would contrast on a color VGA monitor would often be rendered at nearly the same intensity on a monochrome one.

On the other hand, there was no horizontal "granularity" on a monochrome monitor, so the smoothness of the image was impressive.

All in all, it worked best in word processing and other similar software that didn't make demands on one's ability to distinguish shades of gray.
 
Stone said:
And what do 'those things' have in common with a 1991 CRT? That was the point of my previous post! :)
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For that matter what does any of this have to do with your original post... ;-) As Eudi points out, the monitor is capable of an infinite range of grayscales (including 256); the actual number depends on what you connect it to, so this has been about video adapters, not your monitor. Combine the three colours with resistors and feed that into the green pin and how many shades do you get?
 
Stone said:
And what do 'those things' have in common with a 1991 CRT? That was the point of my previous post! :)
Click to expand...

I figured I was missing something in the communications here, but still can't quit figure out what. "Those things" hehe can also have a colour depth issue is what I thought he was talking about.

Regardless, I can't see getting much advantage from a monochrome VGA in terms of images. I've got some and have used them, but don't recall any real excitement with black and white images. Not like the punch of glossies compared to colour prints in the old days. As for rendering colour images in a mono VGA, well that's always an iffy situation. You would have to process every image differently just like you used to in an old fashioned photolab. To me the advantage of of mono VGA are their pleasant look and general VGA functionality in an office or business environment.

As for comparing a CRT to an LCD, I don't think you can. They're completely different beasts and it will come down to what particular features you want. The LCD winning hands down for convenience, but there is of course much more to imaging than that.
 
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