Composite out on CGA is coming out B&W

[VileR]

The text is supposed to look like this: https://int10h.org/blog/2015/08/8088-mph-final-old-vs-new-cga-gory-details/ - the fact that it doesn't probably means that the card uses a different font ROM to the IBM CGA.

The weird part is that the 'normal bootup' photo shows a perfectly normal font which looks just like IBM's ROM. Maybe with a 1-dot horizontal shift, but nothing that could explain the weirdness in the calibration screen.

If this is really one of STB's mono+color combo boards, perhaps it's not quite register-compatible with CGA - something we did on that screen might be triggering the (larger) monochrome font, or sending the card into an 'improper' mode, or some other unintended effect.

 

[voidstar78]

Well, FWIW, I'm running a 1987 edition of KQ1. See bottom of the intro title screen ("1987"). Wasn't there an earlier 1984 PCjr edition? (that's the one with the "king edward dance", and would still run on a regular IBM CGA? I mean, it wasn't PCjr-only? {I never actually had a PCjr, just the tandy 1000 -- which I thought the Tandy's got their own build altogether, probably part of this 1987 release)

In any case, when I just run "kq1.com" it seems to default to the -c / composite option - but I end up with B&W on both outputs. For other games (like Mach3), they startup in the magenta/cyan CGA style (on the CGA output; the composite remains B&W).

EDIT: Speaking of the Williams, note Ken is working on a new game, stay tuned for that. But I'm thinking it'll be a mobile game, not a PC game :D




Below is my "composite" mode (with my setup) just for comparison with the shots earlier.

CTRL+R or starting KQ1 with "-r" command line does run it (on the 9-pin CGA out) with the brown/green/blue colors.






And just for reference, here's what the cables do look like (but my CGA is going through one of those CGA/VGA powered adapters - not shown).





So, it's a weird CGA card I think I've found a reasonably priced IBM CGA, but it'll take a month to get here. We'll see how it turns out!

 

[Trixter]

You're doing everything right; it's just that your CGA card is a clone, and clone behavior was unpredictable. Hopefully your replacement will work out for you.

 

[VileR]

In this case, it's probably predictable - this review of the (original) STB Graphix Plus tells us:

If you use a composite color monitor [...], the colors will definitely be different from those you get with the IBM product, because the Graphix Plus does not have composite color capabilities. Your composite picture will be in black, white, and all the grays in between.

So if this board is anything like the original Graphix Plus, it's not going to do composite in color, period. I'd still keep it, since it seems to have a few nice features, more than just a CGA clone.

 

[voidstar78]

For sure I'll keep it as a backup, or if I ever really need a parallel port. But it has one "bad pixel" in both text-mode and graphics mode (it's the card itself, not the monitor) -- after each boot it consistently shows an incorrect character or blank pixel at the same spot every time.

This is just the card that was in there when I got this 5150. After I noticed the "bad pixel" on it, I tracked down an ISA 8-bit VGA - I knew the 4.77 MHz stock processor can't push VGA modes very well, but it does EGA stuff adequately (and those Sierra titles are rough in classic CGA :D ). But the VGA I found doesn't have a composite out - did anyone make a VGA that also had a composite out?

I never found a Graphics Gremlin - doesn't it support this, VGA out as well as composite out? But I'm horrible at soldering and couldn't assemble one myself, and never found a pre-built one.


Anyhow, thanks all for confirming - for some reason I got it in my head that all Composite out's could do color, so I was just a little surprised this '84 card was still doing B&W-only (esp. since the 9-pin output is doing color). I'll report back when the other "new" (to me) CGA card shows up.


If anyone does know of a Graphics Gremlin, I'd be interested in giving one a try (to avoid having a full length graphics card! :D )

 

[Eudimorphodon]

Anyhow, thanks all for confirming - for some reason I got it in my head that all Composite out's could do color, so I was just a little surprised this '84 card was still doing B&W-only (esp. since the 9-pin output is doing color).

Just for the record, the 9-pin output can’t ”not do” color. It outputs direct digital information that maps directly to the three RGB colors and a brightness control; unless you specifically hook that output to a monitor that chooses to interpret that information as monochrome it’s going to be color.

FWIW, from scanning the docs it looks like the Graphics Gremlin can do its “display CGA or MDA on VGA” trick *or* composite, not both. (The same I/O pin is used across both ports.)

 

[voidstar78]

One card has shown up so far, the "old" 1804472 (appropriate for my 5150 5-slot).

I was disappointed at first, because in the bootup, you can see the font is "messed up" for what should be the color portions of the video. The previous card had "crisp" black and white - but on this card, the colorized text portions look like bar-codes.

But I tried a Composite game anyway "kq1 -c", and it looks surprisingly good. HOWEVER, this Samsung isn't doing the v-sync correctly, the color video rolls (sometimes fast, sometimes slow -- it seemed sensitive to WHEN I connect the Composite cable -- I did that a few times, and each time it seemed the vertical sync ended up differently; i.e. a slow scroll sometimes, or sometimes extremely "wobbled"). I got one screenshot while it was scrolling fairly slowly, so you can see the color is there. [ that rotating-pot thing on the motherboard did effect the colors here -- it was about a 20-30 deg portion of the rotation that had color, while the rest of the orientations did not; but no effect on the v-sync ]

8088mph however didn't go quite well - it did play, but each sequence had different kinds of issues - of course, it's the monitor. I tried a couple different Composite cables, and I tried going through a Composite to HDMI adapter (as well as just straight Composite).

Anyway, still cool to see such nice color out of the old CGA. Not yet playable though, with the v-sync issue. I assume this monitor is also the reason why text-color isn't showing up properly? (in how its interpreting the color) I don't have any other TV/screens with Composite input to try at the moment. I have a slightly newer CGA still on the way.

 

[VileR]

I was disappointed at first, because in the bootup, you can see the font is "messed up" for what should be the color portions of the video. The previous card had "crisp" black and white - but on this card, the colorized text portions look like bar-codes.
[...] I assume this monitor is also the reason why text-color isn't showing up properly? (in how its interpreting the color)

That's actually kind of expected. There's a known issue in IBM's CGA design which prevents 80-column text mode from showing up in color on most composite displays. Those "barcode" stripes are the actual 3.57MHz color information embedded in the composite signal - it's just not decoded properly, since the NTSC color burst isn't being detected. (See https://www.reenigne.org/blog/cga-why-the-80-column-text-mode-requires-the-border-color-to-be-set/)

Color 80-column text is notoriously unreadable on composite anyway. Normally you can just set "MODE BW80" in DOS and get crisp B&W text without the vertical pinstripes. If you really want 80c text in color, some workarounds exist... you can try the utility I wrote for this purpose: https://github.com/viler-int10h/TVCGAFix

Can't say much about the vsync problem. This shouldn't be related to the color issue at all as far as I know, so if your monitor could sync to the STB card in CGA mode, it should sync to this one too. I'd try that other/newer CGA on it and see.

 

[voidstar78]

Could just be a bad "old" CGA? Discounted for a reason maybe :D Well, the RGB 9-pin part is working fine (and in color). Neat that it has the lightpen pins - and I didn't realize the other pin header is for RF output? I do have an RF input on this monitor, kind of tempted to try it... I'll try the TVCGAFix on the weekend, too many other projects right now.


And I need to read about the lightpen again, since I don't understand how that worked - you "draw" on the screen, so how does the screen become an input? I remember seeing the lightpen demo on the PDP-11 once, "drawing" on that 1024x1024 screen.

 

[jafir]

Just in case you aren’t aware, the RF header is for connecting an RF modulator, it won’t output RF on its own.

 

[modem7]

and I didn't realize the other pin header is for RF output?

Just in case you aren’t aware, the RF header is for connecting an RF modulator, it won’t output RF on its own.

Related diagram at [here].

 

[voidstar78]

3rd times a charm? Found a 1501982 that is working nicely with this Samsung LCD.

However, someone had crossed a couple of the lightpen pins together. I didn't notice it, and the system wouldn't power up with the card inserted (whew! glad no damage - no pop, no smoke, think all is ok). I don't think it was a shipping mishap, so a little mysterious about that. Straightened those pins, started right up, and it looks very good to me!

I just noticed 8088mph shows a baby carriage and bottle for NEW during the startup - with the corrupted screen I had with my "old" CGA, I don't recall being able to tell what the icons were for that. Maybe I'll try that old card again to find out. Although it has the "black" bracket, I kind of think a "new" CGA might be more period correct for a B-model 5150 (1983) ? So I'm ready to just button the case back up again.


And as mentioned, yes CO80 text mode didn't show well on bootup, but BW80 looked just fine for DOS text-mode stuff.


Think it's neat the card has the AMD logo and chip on there. Funny how Intel was first "hey, we can put the video stuff right on our chip" (built in graphics accelerators) and then AMD comes back with "hey we can put processor streams right on our video cards" (Ryzen) haha I know it's not exactly like that, but from the casual consumer perspective that's what it looks like. Competition is good - something it seems we're forgetting about with these newer trillion dollar companies.


Here's how things compared with composite vs 9-pin CGA out: (looking fowards trying out other "composite-enabled" titles next weekend including PlanetX )

[ this is the party build - and for the brief moments my "old CGA" was behaved {had sync issues}, it seems the brown was a little better on the old CGA ]

 

[Trixter]

Now you're cooking Glad you were able to source a "proper" card.

 

[voidstar78]

I noticed the symbols used for the "old" CGA: pipe and walker. Epic!

Oh, on the "8088 mph" intro scene - what's up with the 9-pin connector on the bottom left!? Composite is the BiS device, is that the dots further to the left of the 9DB connector?


ALSO - is it possible to retrofit modifiable character set onto a CGA? That was a game changer for EGA and VGA. I know the original CGA hardware cards couldn't be easily retrofitted (without some soldering work), but spec-wise -- could something induce a character change if the character set ROM were instead some writeable chip?

 

[carlos12]

ALSO - is it possible to retrofit modifiable character set onto a CGA? That was a game changer for EGA and VGA. I know the original CGA hardware cards couldn't be easily retrofitted (without some soldering work), but spec-wise -- could something induce a character change if the character set ROM were instead some writeable chip?

Please, someone correct me if I'm wrong...

I don't think it's physically easy (or possible...) to do. The EGA and VGA have a few character sets permanently stored in ROM, and the redefinable characters are stored in RAM. When using the text modes, the RAM characters are stored at A000h segment address, that is, the EGA/MCGA/VGA graphic memory, which is not in use while being on text modes. For doing this on a CGA we would need to have that extra RAM space in some place to store the characters. Too complex, not to say directly impossible, to add an extra RAM chip on an already over populated circuit, which is also not designed for that. Also, the complex chip controller on the EGA/VGA is quite different than the relatively simple Motorola placed on the CGA, so we would need a controller compatible with the CGA but adding the new capability of using RAM charsets. It would be also be interesting to add some functions to the BIOS, although we always can access directly to the ports. We would be finally being transforming the CGA on some kind of EGA.

In my opinion, even if it was possible (I personally think it isn't), it wouldn't be worth at all, as even if we would achieve to add that redifinable character feature to the CGA, still we would not have any software to support it, except the one we would craft for ourselves. The EGA is compatible with CGA monitors, also with MDA ones, albeit with certain limitations on both cases. And VGA cards are not very expensive and a lot of them can be put on PC/XT machines. So, why bother with this?

 

[reenigne]

Yeah, it wouldn't just be a matter of swapping out a ROM chip for an SRAM (DRAM would be much more complicated still as a refresh mechanism would be needed). You'd need logic to coordinate the address coming from the ISA bus with the address coming from the character index. And the data from the ISA bus with the SRAM data lines. You'd need logic to map the SRAM into the address space. You'd need some way to populate the SRAM initially (or you'd boot up to a blank screen) - this is done with an expansion ROM in EGA/VGA cards. If it's done with an expansion ROM too than that would also need to be mapped into the ISA address space.

 

[Eudimorphodon]

Assuming we’re not going all the way into FPGA territory I would hazard a guess you could do it with a daughterboard with, eh, a half dozen chips? And a pretty awful rats’ nest of wiring. I would probably use both a SRAM an a Flash chip programmed with the original character sets, and the addressing hardware would be set up so on RESET the card would default to the flash chip as the character source.

You would need to put multiplexers in front of the SRAM’s address lines for the data load circuitry; if you didn’t care about garbage showing up on the screen when doing loads you could perhaps get away with just one buffer instead of two on the data lines… and then you would need to decide how you expose that memory to the cpu. How hard this will be will depend in part how many jumper wires you want to run and how much cutting you want to do to the card. One thought that occurs is use some latches or an auto-increasing counter to port-load the character ram instead of making it directly memory mapped, it’d save a few wires, but it would also lock out some programming techniques where you might want to update the character glyphs on the fly. De-snow-ing character updates for that would be a challenge…

Or, doh, easy fix to some of the multiplexer and snow issues would be a dual port SRAM. A 2k one would be sufficient. They’re expensive but they do exist.

 

[voidstar78]

Wasn't Sid's game "Pirates!" basically the first commercial success that emulated graphics by using custom font? It was a time when how extensive a game was still limited by what could fit on a reasonable amount of disks - so for the sake of saving disk space, he made a graphical game that used text mode? (IIRC, I had read something about it in Sid's book). And I remember when Norton Utilities had that "graphical mouse" while in text mode - that was wild.

And true, even if CGA could reconfigure fonts, it's back to 16 color? (i.e. you don't gain 1K or 65K colors?). But IDK, maybe if it reconfigure font, it's an easier way to get some video motion playback? And sure, you'd need this custom CGA (maybe a modification of the GraphicGremlin? or just emulators at first) and new software. I'd modify my DestinyHunter to use it (it uses text mode, sort of like the old Kroz games but I used 40-char mode instead of 80).

But was just curious if the "spec" could do it -- i.e. could someone have figured it out before EGA was released and done something it (with a niche CGA-clone card?).

EDIT: Saw @Eudimorphodon response - a daughter board, that'd be wild - people might have bought that, before '85 ?

 

[Eudimorphodon]

EDIT: Saw @Eudimorphodon response - a daughter board, that'd be wild - people might have bought that, before '85 ?

I think most CGA cards have the character generator soldered down and installing such a board "self contained" would require at the least soldering a lot of test points, so if anyone sold such a thing it'd be a pretty niche product.

(If you had a socketed character generator an option would be to put the character memory on a companion card that would plug into its own ISA connector and run a cable to the CGA card; that's be cleaner but you'd lose a slot.)

Re-definable character mods were a thing that were sold for other computers, I'm going to hazard a guess that maybe the most popular one was the 80-GRAFIX mod for the TRS-80, but even that had almost no commercial software support. Usually these were sold as a poor-man's substitute for real bitmap graphics, and of course CGA is all about bitmap graphics so, again, it'd be a really niche thing.

There certainly *may* have been some weird semi-CGA-clone card that threw in redefinable character support, but the oldest non-IBM card I know of that supported it was the Hercules Graphics Card Plus and that actually came out more than a year after EGA. I have no idea how much commercial support there was for it but I suspect it was mostly confined to multi-language word processors.

 

[Trixter]

Wasn't Sid's game "Pirates!" basically the first commercial success that emulated graphics by using custom font? It was a time when how extensive a game was still limited by what could fit on a reasonable amount of disks - so for the sake of saving disk space, he made a graphical game that used text mode? (IIRC, I had read something about it in Sid's book). And I remember when Norton Utilities had that "graphical mouse" while in text mode - that was wild.

I think you're misremembering; Pirates! used a non-traditional graphical font as a way to further stylize the game, suggested by Randall Don Masteller, but the entire game wasn't done in text mode.

Notable games that did use a modified CGA text mode include Round 42, ICON: Quest for the Ring, and Sever Spirits of Ra. There were others, but those are the most common, the latter two having been sold commercially.

A list of many games that used CGA in unconventional ways: https://www.mobygames.com/attribute/sheet/attributeId,5/p,2/