Cheapest way to display CGA

[tipc]

ok, so is the 128's output similar or identical to CGA or not? Clearly it's not analog, I don't think. There's 200 lines of resolution, a separate issue from the ttl/analog question, so that would make it absolutely close to CGA, if the issue of the color being digital, likely, then it's awful close if not identical to CGA.
Others have mentioned the 1084 variants that would display CGA video. Apparently I have that one, or my 1084s is flakey. Again it displayed the 128's output, oh back in early 2011, beautifully. There are other reasons why a monitor doesn't work where it's expected to. It's a bit technical, but regardless it seems if a 1084 displays 128 video, then it logically *should* display CGA, perhaps with a bit of tweaking. Inarguably.

I don't know the 1802, but the 1702 was a fairly decent monitor in my limited experience.

 

[Scali]

ok, so is the 128's output similar or identical to CGA or not?

For the NTSC-models it is identical.
The PAL models use PAL timing, so you get 50 Hz instead of 60 Hz, and more scanlines per frame.

I currently use a 1084S as a CGA monitor for my 8088 machines. Before that I used a Philips CM8833, but that one broke down (both monitors were PAL, and could sync to 60 Hz, but could not decode NTSC colour information over composite).

 

[nestor]

Click to enlarge

Left Commodore 1902A NTSC (120v) CGA / Right Commodore 1084S PAL (230v) EGA emulation

 

[carlsson]

The C128 has two video outputs. It would be the same if you had a PC with two video cards. One is analog, one is RGBI, and it is CGA compatible, at least in NTSC. I have no idea how it works outside of NTSC.

To clarify, the DIN socket on the C128 is used for 40 column video in C128 and C64 modes (or CP/M I suppose, if you want to run it with 40 columns). That socket carries composite video, luminance and chrominance; the two latter make up a signal that roughly resembles S-Video.

The DE9 socket on the C128 is used for 80 column video in C128 and CP/M modes. It carries, just like you describe, RGBI video as well as a B&W composite signal of the 80 column mode. This socket is not usable in C64 mode, at least not if you expect to get VIC-II output in RGB of any kind. Maybe it should go without saying, but many newbies to the C128 believe the opposite, and will get disappointed when they find out the hard way.

Actually in C128 mode you can have one screen connected to each socket. While system I/O will be directed to either display one at a time, you can still output text or graphics to both if you address the chips directly.

For us in Europe, many SCART enabled cables you see on eBay are wired such as you get either composite or luma + chroma from the 40 column mode, and then the B&W composite video from the 80 column mode. While it is possible to make voltage dividers and so on to get the RGBI down to voltage levels of the analog RGB for a regular TV to display, only a few of the cable manufacturers bother about that. It should also be noted that the SCART pinout is designed in such way that one SCART socket on the TV may support RGB or S-Video (they always support composite video), that is why many TV sets have two SCART sockets, one for each of the two inputs. Some newer TV's can be configured which type of input it should take as well. For that matter, making a combined cable that has one S-Video and one RGB input at the same time would have limited use, and in that case you'd be better off with two separate cables and switch input source with the remote, or indeed connect two screens to one computer.

 

[geoffm3]

The Amiga does not have RGBI output.

Actually, according to the reference manuals, it does. Through the same 23-pin RGB output that's normally used for analog RGB. I don't know that anyone has used it but it is an option according to the literature (both owners manual and reference manual). See pins 6,7,8, and 9.

http://old.pinouts.ru/Video/AmigaVideo_pinout.shtml

 

[njroadfan]

Actually in C128 mode you can have one screen connected to each socket. While system I/O will be directed to either display one at a time, you can still output text or graphics to both if you address the chips directly.

Odd that Commodore didn't setup the machine to work with one monitor supporting all modes. An analog RGB output could have easily done it. If Apple figured out how to output legacy Apple II video modes via RGB on the IIgs, Commodore could have done it with the VIC-II in the 128. I wouldn't be surprised if this was yet another factor that curtailed development of C128 software. A relatively complex external adapter could do this in hindsight (S-Video to analog RGB combined with RGBI to analog RGB along with an auto switching setup).

 

[Scali]

Odd that Commodore didn't setup the machine to work with one monitor supporting all modes.

Well, their monitor did support all modes. The 1084S has analog RGB, TTL RGBI and composite inputs. I believe some models even have Y/C input as well.
You could switch with a button on the front, so it was reasonably convenient to use.
I think the problem is that the composite output of the VIC-II was mainly for C64-mode, and those colours are way different from RGBI colours, so there's no point in trying to make an RGBI output.

 

[KC9UDX]

Actually, according to the reference manuals, it does. Through the same 23-pin RGB output that's normally used for analog RGB. I don't know that anyone has used it but it is an option according to the literature (both owners manual and reference manual).

Yes, I stand corrected on that. I never heard of anyone using it, but now that it's been mentioned, I do recall it being there.

Odd that Commodore didn't setup the machine to work with one monitor supporting all modes.

They did. The 17xx, 18xx, 19xx series', and apparently 1084, all do this. The upshot of using two connectors is you can use two monitors if you want.

For some reason, I think they didn't expect people to actually use the VIC-II.

 

[geoffm3]

Which one would that be?

The 1080 does.

 

[vwestlife]

Odd that Commodore didn't setup the machine to work with one monitor supporting all modes. An analog RGB output could have easily done it. If Apple figured out how to output legacy Apple II video modes via RGB on the IIgs, Commodore could have done it with the VIC-II in the 128. I wouldn't be surprised if this was yet another factor that curtailed development of C128 software. A relatively complex external adapter could do this in hindsight (S-Video to analog RGB combined with RGBI to analog RGB along with an auto switching setup).

The C128 was a cobbled-together "three machines in one!" design, and it's a wonder they got it working at all. It bore the legacy of Jack Tramiel's cheapskate ways and used a leftover video chip (the MOS 8563) from an unreleased UNIX machine to produce the RGBI output, and they just kept the old VIC-II chip from the C64 to handle the 40-column modes, with no RGB output possible and colors that wouldn't even match up to 16-color RGBI output anyway.

If you want a good laugh, read "The C128 Story":

http://c128.com/content/c128-story

I just remembered when we found out there was no interrupt facility built in to the 8563. I remember how patient the designer was when he sat me down to explain to me that you don't need an interrupt from the 8563 indicating that an operation is complete because you can check the status ANY TIME merely by stopping what you're doing (over and over) and looking at the appropriate register, (even if this means banking in I/O) or better yet sit in a loop watching watching the register that indicates when an operation is done (what else could be going on in the system besides talking to the 8563 ???) Our running gag became not needing a ringer on the phone because you can pick it up ANY TIME and check to see if someone's on it, or better yet, sit at your desk all day picking the phone up. Even in the hottest discussions someone would suddenly stop, excuse himself, and pick up the nearest phone just to see if there was someone on it. This utterly failed to get the point across but provided hours of amusement.

 

[ClassicHasClass]

I said exactly the same thing until I did some searching around recently. I wanted to know why the 1084 would have RGBI.

So out with it: what was what you found? None of the ads I have here show the 128 with anything other than a 1902.

I certainly believe the 1084 was sold with the C128 late in the 128's life cycle -- the 1084 was even available in a shell which made it resemble a 1902, and I even own one of these -- and whatever internal changes Commodore made to facilitate the 1084 connecting to the C128 were almost certainly to reduce the overhead of manufacturing and storing lots of SKUs. That makes sense. But I've never seen anything to say "The 1084 was marketed for the C128" (emphasis mine), so I'm interested to know what you found that said otherwise.

 

[KC9UDX]

So out with it: what was what you found?

I certainly believe the 1084 was sold with the C128 late in the 128's life cycle

That was what I found. Nothing much more. Being sold with it seems like marketing to me, but I won't lose sleep over it if it isn't.

 

[geoffm3]

Yes, I stand corrected on that. I never heard of anyone using it, but now that it's been mentioned, I do recall it being there.


They did. The 17xx, 18xx, 19xx series', and apparently 1084, all do this. The upshot of using two connectors is you can use two monitors if you want.

For some reason, I think they didn't expect people to actually use the VIC-II.

I think what the previous poster was trying to say is, why didn't Commodore add 80 column video options to the VIC instead of tacking on another video chip (or at least mix the outputs of the video chip's signals together) and display using a single analog RGB video output. That would have made things more seamless.

 

[njroadfan]

I think what the previous poster was trying to say is, why didn't Commodore add 80 column video options to the VIC instead of tacking on another video chip (or at least mix the outputs of the video chip's signals together) and display using a single analog RGB video output. That would have made things more seamless.

....and it would have reduced monitor SKUs right off the bat

 

[Scali]

I think what the previous poster was trying to say is, why didn't Commodore add 80 column video options to the VIC instead of tacking on another video chip (or at least mix the outputs of the video chip's signals together) and display using a single analog RGB video output. That would have made things more seamless.

Well, I think given the timeframe, analog RGB wasn't really an option yet, especially for a home computer.
The Amiga was a high-end machine at the time, so requiring a separate (high-end) monitor was less of an issue. But the C128 was supposed to be the successor to the C64, so it would have to just plug into a simple composite monitor or TV.
Analog RGB monitors didn't really become commonplace until later, with VGA (the friends who had an A500 back in the day, would often use it on a TV as well, not everyone had a 1084S back then).

 

[KC9UDX]

I think what the previous poster was trying to say is, why didn't Commodore add 80 column video options to the VIC instead of tacking on another video chip (or at least mix the outputs of the video chip's signals together) and display using a single analog RGB video output. That would have made things more seamless.

Hindsight is 20/20, and very affordable.

 

[vwestlife]

While the C128 checked off an impressive list of specifications for its time and price range, the CP/M mode quickly became an irrelevanue due to the cliff-like decline in the 8-bit CP/M market, and its 80-column/hi-res mode was unsuitable for games and didn't work on the home TV, so most people just treated it as a C64 with a numeric keypad, more RAM, and a higher price tag.

And even Commodore didn't really intend for it to be any more than a stopgap until the Amiga was released; as Bil Herd commented on my YouTube video about the C128, "all we wanted was one year of not having nothing to show; the next show was going to be the Amiga and the end of the 8-bit era."

 

[Scali]

I think the C128 is more excusable than the Atari ST really. The ST can only display high-res on a monochrome monitor, and only colour on a med-res screen (usually composite out to TV).
The Atari is an all-new design, so they did not have to worry about backward compatibility or anything. I think they made it very impractical this way. I have to plug in my TV when I want to run some games or demos, and plug in my monitor when I want to use Cubase (because you have to use the resolution the software was written against).
On the Amiga, you can use all resolutions and modes on all displays, both TV and monitor. That's how Atari ST should have been.
At least the C128 could still use both modes on the same monitor with the 1084S. Afaik there's no such monitor available for Atari ST.

 

[carlsson]

A few systems, mainly French, offered analog RGB (although the palette would just be 8 colours) in 1984-85 so the tech was there. However I agree with all the other posters that it would have required a redesign of the VIC-II. I'm not even sure that it internally works with anything that could resemble RGB or component video. It would have increased costs, delayed it further and always with the risk of incompatibility. Supposedly there already is a small amount of C64 programs that won't run properly on a C128 in C64 mode; redesigning the graphics chip likely would have broken even more of the compatibility.

If anything, the VDC should've had support for hardware sprites and a bigger palette, but then again Commodore weren't trying to making the ultimate 8-bit gaming computer, rather they were a bit reluctant to gaming and as noted, the 8563 more or less already existed so easier to fix and use it. I don't know how compatible the Apple IIgs is to earlier Apple software, but I get the feeling the custom hardware in the Apple ][ series were less sophisticated and abusable as the C64 chips, so less risks of unexpected usage cases breaking compatibility.

 

[vwestlife]

I think the C128 is more excusable than the Atari ST really. The ST can only display high-res on a monochrome monitor, and only colour on a med-res screen (usually composite out to TV).
The Atari is an all-new design, so they did not have to worry about backward compatibility or anything. I think they made it very impractical this way. I have to plug in my TV when I want to run some games or demos, and plug in my monitor when I want to use Cubase (because you have to use the resolution the software was written against).
On the Amiga, you can use all resolutions and modes on all displays, both TV and monitor. That's how Atari ST should have been.

Well, you can use a VGA monitor with the ST's hi-res mode, even though it came out two years before VGA even existed. And standard TVs and composite monitors don't have enough bandwidth display the ST's hi-res non-interlaced 640x400 mode. In order to make that work they'd need to use interlacing, resulting in the same flickering mess that has been the bane of Amiga users for decades. And with the money that the ST saved you compared to an Amiga, you could afford to buy Atari's hi-res monochrome monitor to go along with it.

At least the C128 could still use both modes on the same monitor with the 1084S. Afaik there's no such monitor available for Atari ST.

With a 15 kHz-capable multi-frequency monitor, like the older NEC Multisync, Mitsubishi Diamond Scan, and Sony Trinitron monitors, ST users can display all modes on a single monitor. (The same as true with AGA-equipped Amigas.)