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B-Series on RGBI Monitor?

KevinO

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Ok, I thought this was going to be easy. I thought that with the right cable, I could connect my B128-80 to a Magnavox 1084 or another Magnavox 80 monitor I have available. The composite output on the B128 is terrible, so I wanted to use the RGBI connector. I sacrificed an old 128 80-column cable so I could put a 5-pin DIN on one end for the B128. I immediately realized this was not quite as easy as I thought. The monitor expects separate Red, Green, Blue, and Intensity (I know, hence the abbreviation RGBI) plus HSYNC and VSYNC, but the B128 only outputs Video, HSYNC, and VSYNC. I tried using just one of the colors to see what would happen. On the Magnavox 80, I got an image that rolls, but nothing at all on the 1084. So I tied the colors all together, same thing. I had no idea what to do with the Intensity line.

Is there a way to connect the B128 to this type of monitor without using the composite input? If not, do I need a true monochrome monitor for this computer? Steve Gray, what are you using with your B-Series?
 

sjgray

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I still use the monochrome monitor that I got from Protecto ;-) It gives a nice clear picture using its composite connector. I have a lot of stuff, so sometimes the mono monitor gets put away, in which case I use a Poloroid LCD or sometimes a 1084. I do notice some tearing or contrast problems at the very top when using the LCD, which I assume is the mono signal being too strong or the frequency being a bit off.

http://www.6502.org/users/sjgray/temp/B128-with-mono-monitor.jpg
http://www.6502.org/users/sjgray/temp/B128-with-polaroid-lcd.jpg
http://www.6502.org/users/sjgray/temp/B128-with-polaroid-lcd-and-drives.jpg
http://www.6502.org/users/sjgray/temp/B128-with-polaroid2.jpg


Sorry, I don't have a picture of the B128 and 1084. I've tried other monitors as well with varying success. I wouldn't call the B128 composite output terrible. Most color composite monitors can not handle the 80 column signal. I've never tried using the Video/H-sync/V-sync output but I imagine it should work (it's basically the same signals that the PET monitors use).

If you want me to test something for you let me know. I have a few other monitors around ;-)

Steve
 

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evildragon

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I've never tried using the Video/H-sync/V-sync output but I imagine it should work (it's basically the same signals that the PET monitors use).

That's the same even my model 25 uses (monochrome model). It does however differentiate in horizontal frequency, and in one mode, also the vertical frequency.
 

sjgray

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That's the same even my model 25 uses (monochrome model). It does however differentiate in horizontal frequency, and in one mode, also the vertical frequency.

The IBM Model 25 has a VGA monochrome monitor, so it's 30kHz. We're referring to mono TTL -type monitors, generally at 15kHz.
There are converters (scan doublers) available that could convert 15 to 30. The go for about $25-30 on ebay. They're designed for Arcade RGB systems.

Steve
 

evildragon

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The IBM Model 25 has a VGA monochrome monitor, so it's 30kHz. We're referring to mono TTL -type monitors, generally at 15kHz.
There are converters (scan doublers) available that could convert 15 to 30. The go for about $25-30 on ebay. They're designed for Arcade RGB systems.

Steve

I understand, it's why I said it differentiates in horizontal frequency. Model 25 isn't a true VGA monitor, doesn't support EGA 350 line mode, but yes, it's video input is analog, but it's still in the form of Video/H Sync/V Sync, just like the model 25.
 

patscc

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I seem to remember reading about a fairly-simple, TTL, 74XX based scan doubler when I was a kid.
My problem is I grew up here and over-seas, so I can't accurately remember if I saw it in Radio-Electronics, Elektor, Elrad, or something else entirely.
I realize this post is probably more than useless to the OP, but I'm hoping it will jog someone's memory, and they can dig up a schematic.

KevinO, do you by any chance have any multi-sync type monitors laying around ? If so, check their specs to see if they can sync down to 15.7 kHz or so, then you might be able to get it to work by
patscc
 

KevinO

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Strange...my PC was just loading a cached page and not showing me updates. I thought it was odd that I had no responses in this thread!

Anyway, I don't have any multisync monitors. I have an Idek that I've been meaning to try to repair, but never gotten around to it. Anyway, I thought there should be a way to output mono video into an RGBI connection, but apparently that's more difficult than it would seem. My monitors are all either Magnavox RGB or Commodore 1702, 1902, or 1084, so I was hoping to make it work with one of those. Steve, as you said, the composite results are mixed. On one of my 1084s, it has the tearing at the top of the screen. On the Magnavox CM8762, composite works, but the quality is poor.

I seem to remember reading about a fairly-simple, TTL, 74XX based scan doubler when I was a kid.
My problem is I grew up here and over-seas, so I can't accurately remember if I saw it in Radio-Electronics, Elektor, Elrad, or something else entirely.
I realize this post is probably more than useless to the OP, but I'm hoping it will jog someone's memory, and they can dig up a schematic.

KevinO, do you by any chance have any multi-sync type monitors laying around ? If so, check their specs to see if they can sync down to 15.7 kHz or so, then you might be able to get it to work by
patscc
 

vwestlife

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The B128 is only monochrome, right? Composite video is entirely adequate for displaying very crisp and sharp monochrome 80-column text (and similar hi-res monochrome graphics), as long as you're using a monitor which allows the full bandwidth to be displayed.

Television sets and color composite monitors have a maximum video bandwidth of 3.5 MHz, due to the presence of the NTSC color subcarrier at 3.58 MHz. (This is true even on black & white TV sets made since the late 1950s, because they need to filter out the color subcarrier to prevent it from causing interference on the image.) This bandwidth is not adequate for crisp 80-column text, even in black & white.

A monochrome composite monitor specifically designed for computer use, however, will have a much higher video bandwidth (up to 6 MHz), which will give a much higher quality image. This also includes some color composite monitors with a special high-bandwidth monochrome 80 column mode, such as the AppleColor series of color composite monitors designed for the Apple II series.
 

patscc

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vwestlife said
Television sets and color composite monitors have a maximum video bandwidth of 3.5 MHz,
Actually, it's not quite that simple, because of how the color subcarrier is modulated.
spec_ntsc_col.gif

patscc
 

evildragon

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I have some old TV's, where if fed a monochrome composite signal, will shut off color circuitry to allow much higher resolution monochrome image. My old tube hybrid Hitachi TV does that, but my Samsung SS set from the mid 80's does not. Also seen a modern KLH 32" CRT TV from a few years ago, DID do this though too.. So it seems to be hit or miss on what set is capable of full bandwidth monochrome use.
 

KevinO

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Ok, I think we're still on topic....

So from the responses so far, it sounds like it's composite or I need a true monochrome monitor. I'm still surprised there's no way to do this with an RGBI monitor.
 

sjgray

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vwestlife

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It should be possible to display TTL monochrome 15 kHz video on a Commodore 1084 or other similar RGB/RGBI monitor as long as you switch it into digital (TTL) RGB mode (not analog) and tie the computer's video signal output to all three colors (R, G, B) to get a white display. Most monochrome monitors only use the "green" pin, but I don't know if Commodore monitors are smart enough to detect that (video on G but nothing on R or B) and switch into a monochrome mode.

In practice, though, TTL monochrome 15 kHz video is rather rare, as most other computers with a similar monochrome output used higher scanning rate to get higher resolution on the screen, such as 18.4 kHz for IBM's MDA (720x350), 22.25 kHz for the Mac 128k/512k/Plus/etc. (512x342), 26.4 kHz for the Tandy 2000 (640x400), etc....
 

carlsson

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FWIW, I'm using a green & black Philips monochrome monitor with my CBM 610. Very crisp display, far better than any of my 1084's or TV's. Maybe I should try one of my Sony Triniton monitors though, those seem highly capable when it comes to inputs, not sure about dot pitch.

When it comes to PET/CBM-II sync frequencies, I didn't have much success in my previous homemade adapters but perhaps feeding the sync signals as they are to the monitor would work. I never considered that option since I've got a monochrome "composite" monitor already.
 

KevinO

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In practice, though, TTL monochrome 15 kHz video is rather rare, as most other computers with a similar monochrome output used higher scanning rate to get higher resolution on the screen, such as 18.4 kHz for IBM's MDA (720x350), 22.25 kHz for the Mac 128k/512k/Plus/etc. (512x342), 26.4 kHz for the Tandy 2000 (640x400), etc....

This is the piece of the puzzle I didn't have. I assumed that the mono output of the B128 was 15KHz, since it already has a composite output which we know is 15KHz. It never occurred to me that it might be different. If indeed it is MGA, then I can see why it wouldn't work. I was remembering connecting my C128 80-column output to a mono monitor years ago, and assumed that if you could plug color output into a monochrome monitor, you should be able to display monochrome video on a color monitor using the TTL RGB connector.

Steve, I did look over that video conversions doc, and saved a copy for future reference. Fascinating document.

I'll see if someone's got a mono monitor at VCF next month. If you guys are saying that the composite ones look fine, that's what I'll try to get. At least I don't have to mess around with making cables then!
 

reenigne

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I seem to remember reading about a fairly-simple, TTL, 74XX based scan doubler when I was a kid.
My problem is I grew up here and over-seas, so I can't accurately remember if I saw it in Radio-Electronics, Elektor, Elrad, or something else entirely.
I realize this post is probably more than useless to the OP, but I'm hoping it will jog someone's memory, and they can dig up a schematic.

As it happens, I have just such a scan doubler in the form of an ISA card for IBM PC/XT machines. It only uses the ISA bus for power and the 14.318MHz clock, though - the input and output are both CGA RGBI TTL 9-pin d-sub connectors (I have no idea what sort of monitor accepts an RGBI TTL signal at 31.4KHz line rate). Also as it happens, I recently reverse-engineered the board to a schematic, which I've put online at http://www.reenigne.org/misc/scan_doubler.pdf . It's not exactly simple at 25 chips but it is all discrete 74Sxx logic plus a small amount of RAM for the line buffer. Hope it's useful to someone!
 

sjgray

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Here is the board I was mentioning earlier: Ebay # 380464329867

It supports 15kHz input CGA (RGBI) to VGA (multiple frequencies). Cost about $25.
I have a board similar to this I picked up a couple years ago but have not had a chance to try it. Originally I was planning to try this on the C128 but I think it should work on the CBM-II machines or even PET.

I would think that feeding the B128 Video/Vsync/Hsync to the CGA input should work since CGA accepts 0 to 5v signals. I am not an electronics person so try at your own risk ;-)

Steve
 

KevinO

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Interesting. I've seen these for a much higher price elsewhere. You should see if it works on the B128 and let us know! But if you're like me, you've got 100 other projects waiting in line to be finished.

Thinking about it, I think the problem would be the same. The RGBI input expects separate red, green, and blue inputs, so which one to connect to? Green, I suppose. But if the other poster was correct, and the output of the HSYNC is something other than 15khz, then it wouldn't work. I should plug in my scope and see what's actually coming out on that pin.
 

carlsson

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Yes, $25 for a RGB/CGA to VGA converter sounds like it is on sale but perhaps prices have dropped recently. The one I got last year was more in the $35-40 range, although including free overseas shipping.

Since my 610 and my CTX mono/CGA/RGB monitor are just a meter apart (facing different directions), I might very well have a go with a DIN to DE9 cable and see if I get any good output on the monitor, better than the mono Philips monitor that I'm currently using.
 
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