Ibm ega +/- composite video modification questions

[Hugo Holden]

I have been looking at the idea of fitting an IBM EGA card to my 5155. The card does not support composite video. But the 5155 uses an internal composite monochrome monitor, receiving its output from the CGA card. Looking at the CGA's schematic the monochrome composite signal is derived in the usual way (common to early Atari video games) by XOR'ing the H & V sync pulses and mixing those resistively with proportions of the red ,green and blue signal to create a composite luminance signal.

Why did IBM drop this output from their EGA card ?

It appears though that all the information is present on the feature connector of the EGA card, R,G & B to mix together and H & V retrace from which I could organize composite H&V sync pulses to generate a monochrome composite signal. Did IBM or any third party sell a feature adapter that did this and is any information available on it ?

One concern is that it would be necessary to keep the EGA card out of the 24kHz high scan rate mode as the H sync circuits in the 5155's internal monitor could not lock to that, but I think its a conventional free running H scan circuit in the 5155's internal monitor, like an ordinary TV monitor, so it would not be damaged.

Also the ATI wonder 400 EGA card appears to have a composite output already there, so what happens to the H scan (sync frequency) rate on that composite output when the EGA card is in the 24kHz mode, does it maintain the usual rate around 15kHz ?

Finally, there is one EGA card which is short and will work in slot 8 as it has a jumper for this, this is the VEGA card from Video-7. Also it is said to be able to coexist with the CGA card. With two cards in situ would they display graphics simultaneously, thereby allowing the continued use of the composite connector on the existing CGA card ?

 

[vwestlife]

With the use of interlacing it would be possible to display 640x350 or even 640x400 graphics on a 15.75 kHz composite or CGA monitor, at the expense of visible flicker. The ATI Small Wonder does this to display 720x350 MDA/Hercules video on a composite or CGA monitor, but I haven't heard of a video card which uses interlacing to display hi-res EGA graphics on composite video. Given the limited resolution of TV sets and color composite monitors in the 1980s, it was probably thought of as not worth the effort, because all the fine detail of hi-res EGA graphics would come out rainbow-streaked and illegible.

 

[reenigne]

Why did IBM drop this output from their EGA card ?

Probably because of lack of demand. Even with CGA, use of the composite output was rare compared to the RGBI TTL output. Those who could afford an expensive IBM PC could generally afford a dedicated monitor to go with it.

It appears though that all the information is present on the feature connector of the EGA card, R,G & B to mix together and H & V retrace from which I could organize composite H&V sync pulses to generate a monochrome composite signal. Did IBM or any third party sell a feature adapter that did this and is any information available on it ?

Not as far as I know. In fact I've never seen anything that plugs into the feature connector. Though from the design of the EGA's feature connector (and especially the fact that a pin it goes to a cinch connector on the rear) it's clear that a composite output feature module was one of the (if not the) applications that IBM had in mind for the feature connector.

One concern is that it would be necessary to keep the EGA card out of the 24kHz high scan rate mode as the H sync circuits in the 5155's internal monitor could not lock to that

I think the EGA (at least the IBM one) has a DIP switch for that - it's what you'd use if you were connecting your EGA card to a CGA-frequency RGBI monitor (like the 5153).

Also the ATI wonder 400 EGA card appears to have a composite output already there, so what happens to the H scan (sync frequency) rate on that composite output when the EGA card is in the 24kHz mode, does it maintain the usual rate around 15kHz ?

I don't know that card specifically, but I'd be very surprised if it did - that would require a fair bit of duplicated hardware for a relatively little-used feature. I expect it has a DIP switch or similar, like the IBM EGA.

Finally, there is one EGA card which is short and will work in slot 8 as it has a jumper for this, this is the VEGA card from Video-7. Also it is said to be able to coexist with the CGA card. With two cards in situ would they display graphics simultaneously, thereby allowing the continued use of the composite connector on the existing CGA card ?

Most (if not all) graphics cards which can coexist with CGA do so by running in mono mode (i.e. using memory at 0xb0000-0xb7fff instead of 0xb8000-0xbffff and ports 0x3bX instead of 0x3dX). So it might be able to do graphics if can emulate (e.g.) Hercules. Though most software that is aware of the CGA+mono combination will only drive the mono card in text mode (handy for debugging CGA software as you can have your debugger on the mono screen and your program's output on the CGA screen).

 

[Scali]

but I haven't heard of a video card which uses interlacing to display hi-res EGA graphics on composite video. Given the limited resolution of TV sets and color composite monitors in the 1980s, it was probably thought of as not worth the effort, because all the fine detail of hi-res EGA graphics would come out rainbow-streaked and illegible.

Amiga does this. You can get 640x480 interlaced NTSC or 640x512 interlaced (+overscan) on PAL.
It's not that bad actually, although you will run into contrast-issues with small details, so for text it wouldn't be that great. For photorealistic stuff however, it worked very nicely.
In fact, later VGA cards tended to come with s-video TV-out, which also gave you that same interlaced resolution. You could also convert it down to composite with simple dongles if your TV didn't have s-video input. You can also buy simple external devices that do the same: convert the analog VGA down to NTSC or PAL. I've used this to capture video from my 486 VGA.
I used to run my screen at 1024x768 or 800x600 and let the hardware downscale that to PAL.

So I think that's one thing you could do: put a VGA card into your 5155, and then use one of these babies to make it composite, then run that to the internal monitor:
http://www.konigelectronic.com/en_us/computer/video/55998309

 

[reenigne]

So I think that's one thing you could do: put a VGA card into your 5155, and then use one of these babies to make it composite, then run that to the internal monitor:
http://www.konigelectronic.com/en_us/computer/video/55998309

There are even some VGA cards that can do composite output directly (at 15kHz line rate, while the VGA output is at the normal 31kHz+ line rate) but I doubt any of those are ISA cards.

 

[Scali]

There are even some VGA cards that can do composite output directly (at 15kHz line rate, while the VGA output is at the normal 31kHz+ line rate) but I doubt any of those are ISA cards.

I saw an ET4000 ISA card like that recently, on Vogons: http://www.vogons.org/viewtopic.php?f=46&t=46199
Probably quite rare.

 

[vwestlife]

So I think that's one thing you could do: put a VGA card into your 5155, and then use one of these babies to make it composite, then run that to the internal monitor:

Actually with a monochrome composite monitor, like the IBM 5155's internal CRT, you would get far better results taking only the luminance (Y) pin of an S-Video output. That way you get full-bandwidth monochrome video without any color subcarrier interference. I used that trick to get pretty well legible 800x600 video on a mono composite monitor:

 

[Hugo Holden]

Thank you kindly Scali, vwestlife and reenige for the help and advice.

I have a vintage IBM EGA card(with the memory expansion) on its way. Its the same age as the computer. When I get it I will set it to drive my 5153 monitor. I will look at the signals and design a "feature" adapter for it to create a monochrome composite signal (without a color subcarrier keeps it simple) to drive the internal IBM amber monitor. If it all works out I will post a link to its design.

(I must say I am very impressed with that internal amber monitor in the 5155, it has high brightness and contrast, maintains focus well over the whole screen area and it has excellent both horizontal and vertical scan linearity and its a great screen for text...so I think the designers did a terrific job on it. For example I have a couple of green phosphor Apple IIc composite monitors about the same size and all of those factors mentioned are not quite as good, though still "ok")

In my case the main reason to change the CGA card is to gain a better color palette than the very limited CGA palette for some simple graphics, hopefully the 8 colors + 8 intensified ones. I don't particularly need high resolution graphics or more colors than that. I have looked at the data on the IBM EGA card on minuszerodegrees, but I wasn't sure from that if I could definitely get at least a simultaneous 8 or 16 color palette, in a 320 x 200 graphics mode with the 5153 monitor and the IBM EGA card working together ?

 

[modem7]

I have looked at the data on the IBM EGA card on minuszerodegrees, but I wasn't sure from that if I could definitely get at least a simultaneous 8 or 16 color palette, in a 320 x 200 graphics mode with the 5153 monitor and the IBM EGA card working together ?

IBM's technical document ([here]) on the EGA card includes, "... full 16 color support in both 320x200 pel and 640x200 pel resolutions for the IBM Color Display"

From the magazine article at [here], "The EGA also has two new graphics modes that can run on the IBM Color Display. Mode 13 displays 200 lines of 320 dots with l6 colors. Two video
pages are available with 64K, four with 128K, and eight with 256K. Mode 14 displays 200 lines of 640 dots, also with 16 colors but half the number of video pages."

 

[Scali]

IBM's technical document ([here]) on the EGA card includes, "... full 16 color support in both 320x200 pel and 640x200 pel resolutions for the IBM Color Display"

From the magazine article at [here], "The EGA also has two new graphics modes that can run on the IBM Color Display. Mode 13 displays 200 lines of 320 dots with l6 colors. Two video
pages are available with 64K, four with 128K, and eight with 256K. Mode 14 displays 200 lines of 640 dots, also with 16 colors but half the number of video pages."

Yes, to expand on that... These are all the 'textmode' colours from CGA, so the fixed RGBI set.
On an EGA monitor in 350-line mode, you can use 16 colours out of a total of 64, because each colour has its own intensity line.
Sadly, IBM chose not to enable the extra colours in 200-line modes at all, not even on an EGA monitor.

 

[g4ugm]

Why did IBM drop this output from their EGA card ?

Probably a display quality issue/usability issue. The EGA card generates a 23Khz when operating in 350 line mode so a normal screen won't lock. Anything that can do 23Khz will also accept RGB.

More cynically , so it could sell more EGA monitors?

 

[Scali]

It could also have to do with product placement/differentation. EGA was supposed to be the high-end/professional solution. Connecting to a TV was something you'd do with a home computer like the PCjr.
I am actually more puzzled by IBM's choice to put composite on their CGA card. Not many people would use a business machine with a TV as monitor. It's no good for 80-column textmode, and the 160x200 resolution in 16-colour composite mode is not going to be very useful for any kind of charts or presentations either.
Including ROM BASIC and cassette storage are two more choices that don't seem to make sense for a business machine, but they mimic what other home computers were doing at the time.

To me it seems that the PC was originally meant to be both a home and business computer at the same time. But when others started their pricewars, there was no way for IBM to compete, so they tried a cut-down budget version for the home instead, in the form of the PCjr. At that time, the PC had already carved out its niche as a business machine.

 

[Hugo Holden]

It appears that there were two uses for the composite signals. One for external monitors, be it monochrome or color, with their limitations and primarily for home use rather than professional use, but secondly in the unique case of a 5155, a signal for the internal monitor. So I guess IBM had/needed the composite signal there anyway for the 5155. Though looking at their schematic of the CGA card, they did go to quite a bit of trouble to make the composite output color, when that wasn't needed for the internal amber monitor. Maybe the industry was in flux on these points. It is interesting that most third party manufacturers of EGA cards didn't have a composite output, even one for a monochrome internal monitor. But all this makes me think the 5155 is a unique machine having that lovely amber on board monitor.

It also appears that some EGA cards, like the IBM, should essentially be plug & play, or only DIP switches needing attention. I think this is the case with IBM's card. But others there is more dependence of software support to control them. For example utilities were provided with the Video-7 EGA cards to help control them, but as time goes by the software (disks) part company with the hardware. I have also acquired some VEGA Video-7 EGA cards to try but the supporting software might be unobtainium ?

In the meantime I got some QuickBasic V4 5.25 floppys to try. I really would have expected the magnetic dipoles would have faded away. Most VHS tapes from the 1980's now play as "snow" for example. But astonishingly they worked and I have been able to create EXE files of basic programs. Much to my surprise also, in the demo programs on the disks was a Mandelbrot graphic, see attached image. I think this is very special and captures the magic of these early computers and their programs.

 

[Scali]

It appears that there were two uses for the composite signals. One for external monitors, be it monochrome or color, with their limitations and primarily for home use rather than professional use, but secondly in the unique case of a 5155, a signal for the internal monitor. So I guess IBM had/needed the composite signal there anyway for the 5155.

The connector is actually for an optional RF-module, so you can connect your CGA to a regular TV via the antenna input (composite inputs on TVs were rare in the late 70s/early 80s).
IBM abused the header for the 5155 because it basically gives you an internal connector for the composite signal.

Though looking at their schematic of the CGA card, they did go to quite a bit of trouble to make the composite output color, when that wasn't needed for the internal amber monitor.

In fact, IBM modified the output circuitry, because the original design from 1981 only had two distinct luminance values for the 16 colours.
The updated circuit tweaked the colours somewhat so you'd get 16 distinct luminance values, which they probably did for the 5155's internal screen (or perhaps there was a demand in general for better monochrome composite even before that time).

Maybe the industry was in flux on these points. It is interesting that most third party manufacturers of EGA cards didn't have a composite output, even one for a monochrome internal monitor. But all this makes me think the 5155 is a unique machine having that lovely amber on board monitor.

IBM EGA doesn't have composite output either. Only CGA does.

It also appears that some EGA cards, like the IBM, should essentially be plug & play, or only DIP switches needing attention. I think this is the case with IBM's card. But others there is more dependence of software support to control them. For example utilities were provided with the Video-7 EGA cards to help control them, but as time goes by the software (disks) part company with the hardware. I have also acquired some VEGA Video-7 EGA cards to try but the supporting software might be unobtainium ?

All video cards should be plug & play. That is, as soon as you power up your machine, it should work.
The utilities are usually just to enable/disable special features, eg, to switch them to CGA-compatibility mode, or to set the frequencies for certain resolutions for an SVGA monitor etc.
They may also contain specific drivers for Windows, WordPerfect, Lotus 1-2-3 and other software that may use custom display modes.
You won't need them for everyday use.

 

[bjt]

Nice to see your 5155 is being looked after!

I use a Video 7 VEGA in my Tandy 1000. Can confirm the feature connector works fine, I use it to switch between EGA and Tandy video output. The utility disk contains some diagnostics and a TSR to enable register-level CGA compatibility, which seems to work well. Otherwise it's not needed.

Manual: http://minuszerodegrees.net/manuals...hics Adapter (VEGA) - Users Manual - 1985.pdf
Software: http://minuszerodegrees.net/manuals/Video Seven - VEGA Deluxe - Utility Disk - Version 2.02.zip

 

[Hugo Holden]

Yes, and as another example I noticed on the early Wonder 400 cards that DIP switches were used to select modes/monitors etc. But for example on the 800+ Wonder card the physical switches had vanished from the pcb and they had become "software switches" So I was assuming, that without the original manufacturer's utilities this could be an awkward situation ?

 

[Hugo Holden]

BJT, Thanks for that link to the video-7 utilities, that will make it easier to try the video-7 cards out in the 5155.

I was very lucky to get a 5155 in such good order, especially shipped Air post from the USA to Australia. When I got it it was fitted with two 5.25 floppy drives. After a lot of pondering I decided it would have to have a hard drive in it, so I got a vintage Seagate 40Mb drive and I think the controller is an ST11R. Its a good thing it takes so long to boot up as it gives the massive platter in the drive time to get up to speed. It took me ages to figure out how to low then high level format the drive but I got there in the end, steep learning curve. Also I fitted a dual 5.25/3.5 drive to the other bay and set the 5.25 as drive A because some early games like Paperboy need to start in the A drive. I then loaded it with DOS 3.3 so it supports a 1.44Mb floppy format and I loaded it with Windows V1.0. The 3.5 drive is handy to transfer data into & out of the computer. I had considered one of those USB drive emulators, but somehow that didn't fit with the vintage theme. It is also fitted with the classic six pak plus card and it has a total of 640 kB of memory as it also has a memory expansion card.

In any case I'm impressed with the design of the 5155, I think the whole thing right down to its beautiful pcb's with DIL IC's and through hole parts is a total masterpiece. After all, it is still working 32 years on, I can't see that happening with an iPad. Also it has a 2001 Space Odyssey like appeal. It is sort of "portable" if you have a strong arm and it is a "desktop" computer in that it occupies most of the desktop. It also has the best feeling keyboard of any computer. It really makes you think how clever the designers at IBM were. There were other companies that excelled in this era too, like Tektronix, where excellence was the name of the game.

 

[bjt]

I had a 5155 in the early 90s, unfortunately it had some issues and I didn't know enough to fix it.
Ended up selling it on after the PSU gave up the ghost. I should have kept it!

They are cool, but I'm not sure about brilliant hardware design... they're basically an 5160 XT motherboard shoehorned into a case with a monitor.
The flipdown keyboard is the same as the XT's too. They're impressively sturdy, certainly

 

[lowen]

There are even some VGA cards that can do composite output directly (at 15kHz line rate, while the VGA output is at the normal 31kHz+ line rate) but I doubt any of those are ISA cards.

I'm holding in my hands a Willow Peripherals VGA-TV card that is an 8-bit ISA VGA with a composite out. Made in 1990. Tseng Labs ET3000AX-based.

 

[Hugo Holden]

I had a 5155 in the early 90s, unfortunately it had some issues and I didn't know enough to fix it.
Ended up selling it on after the PSU gave up the ghost. I should have kept it!

They are cool, but I'm not sure about brilliant hardware design... they're basically an 5160 XT motherboard shoehorned into a case with a monitor.
The flipdown keyboard is the same as the XT's too. They're impressively sturdy, certainly

Yes, bjt, they did sort of shoehorn the mother board in. But the thing I like is the whole computer is repairable, good documentation at the pcb/circuit level, many IC's in sockets etc. Looking at many modern appliances with the move to surface mount, poor documentation etc its more difficult to work on them to keep them going. For example by the 1990's Tek had moved to surface mount parts in the CPU board for their 2465b scopes. They used surface mount electrolytic caps which leak 20 years later and eat through tracks and the conducting films in surface mount resistors. The small sized parts are less robust to insults like this. It sets the life of the pcb to about 20 to 25 years. I have repaired a few but the damage is diabolical. These electros are still very popular in many devices today. It is really "built in obsolescence" guaranteed for a lot of modern machines. A similar situation applies to vintage vs new cars. So with the 5155, and the 5153 monitor, they are good and fun to work on. For my 5153 so far all that was needed were a few new capacitors in the gun drive circuits. The output coupling capacitors from the R,G & B video output stages, which were 2.2uF electros are better changed to poly caps for lower electrical leakage and long term reliability, this was not a good circuit position or application for an electrolytic capacitor.