C=128 80Col NTSC Color.
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From: a7yvm109gf5d1 on 15 Mar 2007 20:53 On Mar 13, 6:29 pm, "Pheuque" <Goo...(a)joetomcollins.com> wrote: > http://www.twobits.com/RGB/rgbman.html > > This claims to allow CGA signal to be output to a NTSC or PAL > compatible monitor. It designed for maintenance and modification on > older video cabinet systems. > > The $200 price tag seems insane, but the actual circuit board doesn't > seem to be too complicated. > > I would love to be able to use 80 Col color on my old Commodore 128s. > My 1084 is gone, and finding a CGA monitor these days isn't so easy. > > I know others have looked at methods to get VGA out and failed. > Perhaps we're working to hard. Maybe going to NTSC or PAL first will > get us an acceptable signal. It's only 640 x 200 or or 640 x 400 > interlaced. With that a simple switch box and an NTSC to VGA adapter > would do the job. > > Does any one have more information on this board? Be nice to drive the > cost down a bit. I agree the price is insane. Maybe if the board had no solder mask the price would go down a lot. I also don't see how this can work with CGA. As I've mentionned, there really is nothing in common with the RGBI timings and what a color TV expects. You really need more than a handful of resistors and a tiny IC to fix the inherent, fundamental mismatch between the two. It's like trying to listen to 101.3 WXCL but the radio is tuned to 97.8. First, look at a typical horizontal line in NTSC. Now look at a horizontal line in RGBI. Only about 2/3 of the line has actual pixels in it. Out of the 1016 clock cycles for a line, only 640 are pixels. This is why the 128's 80 column output is so much narrower than the 40 column display. NTSC lines are much fuller, the front and back porches much shorter. If you change the 16MHz crystal in the 128 to a 14.31818MHz crystal, and you can predict the behavior of the rest of the machine (I can't, I'd have to look), you'd have a much better chance of encoding RGBI into blurry NTSC. I'm not even sure if you can program the VDC to output the correct sync frequency with a 14MHz crystal. It's something to try to finally lay this horse to rest.
From: Rick Balkins on 17 Mar 2007 12:46 Some CGA is 16 colors. Some is 8 colors. Most just deal with CGA's first 8 colors. You probably can do oneself a better deal to convert the RGBI into Analog RGB, first - and then scan double it. How do you do it? There is a board in your RGBI monitors like 1902A that takes the digital RGBI (4 digital bits) to make the Analog R,G, & B lines. Basically, remake that card but external of a monitor and add a scan doubler - and it ought to work. CGA originally was 8 colors and then CGA was extended further to 16 colors with many of the cards but the most earliest of them. The biggest problem is these guys don't tie in the Intensity line to each of the R, G and B DACs. I is tied in and basically the DACs are 2 bit DACs. One bit would be the 'color' bit and the other would be the 'intensity bit'. However, the intensity bit is tied to ALL R,G,B DACs at the same time. However, if you seperated the Intensity bit or say added too more bits from say the user port, you could theoretically increased the color options to 64 colors but there will be some sort of limits caused by CIA not being synced with the VDC so it is all timing. Your best timing is character clock timing, that is about it. So in theory, you could increase the intensity option externally from the user-port for example. This was among part of the concept presented to A7yvm.... since RGBI was so digital. Basically, the RGBI lines (with exception to the clock lines (syncs), is basically not much different to any of the I/O on the C64/128. "Brian Ketterling" <tweel6510(a)no-potted-meat-products-peoplepc.com> wrote in message news:b3QJh.9784$PL.2948(a)newsread4.news.pas.earthlink.net... > "Mangelore" <fotios(a)commodore128.org> wrote in message > news:7KOJh.10962$8U4.9123(a)news-server.bigpond.net.au >> Please note that these "CGA to VGA" or "CGA to PAL/NTSC" converters do >> not display the full 16 colours as they do not support the intesity >> output of the C128. They are RGB CGA devices, not RGBI. So, you'll only >> see the first 8 colours. > > I thought CGA was 16-color RGBI, with a two-level "I" signal. When I > connect my old Zenith CGA monitor to my 128, I see 16 colors. > > Brian > -- > >
From: Rick Balkins on 17 Mar 2007 12:49 The problem is they used one bit DACs for the R,G, and B. If you find out that those DACs are more than 1 bit - then you can tie the Intensity lines to the R,G & B DACs and voila - 16 colors. Just takes a few wires. However, it is likely all integrated into a single chip and you would have to look at the specs of the chip itself - if it has an Intensity input pin and tie it there and voila. Those cheap ________, doesn't think about that. "Mangelore" <fotios(a)commodore128.org> wrote in message news:koRJh.11039$8U4.2925(a)news-server.bigpond.net.au... > While I agree with you that CGA was RGBI, these converters to not process > the "I" signal. The only have inputs for R,G,B,V,H,GND. > > Cheers > Fotios > > Brian Ketterling wrote: >> >> I thought CGA was 16-color RGBI, with a two-level "I" signal. When I >> connect my old Zenith CGA monitor to my 128, I see 16 colors. >> >> Brian
From: Patrick de Zeester on 17 Mar 2007 13:11 Rick Balkins wrote: > Some CGA is 16 colors. Some is 8 colors. That is new to me. Are there any sources that support your claim that there were 8 color CGA adapters? > Most just deal with CGA's first 8 colors. Really? The only variation I'm aware of how CGA monitors treated the intensity bit i.c.w. the black and yellow colors. > You probably can do oneself a > better deal to convert the RGBI into Analog RGB, first - and then scan > double it. How do you do it? There is a board in your RGBI monitors like > 1902A that takes the digital RGBI (4 digital bits) to make the Analog R,G, & > B lines. > > Basically, remake that card but external of a monitor and add a scan > doubler - and it ought to work. CGA originally was 8 colors and then CGA was > extended further to 16 colors with many of the cards but the most earliest > of them. CGA introduced by IBM supported 16 colors from the start (1981). I really wonder where you get your information from.
From: Patrick de Zeester on 17 Mar 2007 13:27
Rick Balkins wrote: > "Mangelore" <fotios(a)commodore128.org> wrote in message > news:koRJh.11039$8U4.2925(a)news-server.bigpond.net.au... >> While I agree with you that CGA was RGBI, these converters to not process >> the "I" signal. The only have inputs for R,G,B,V,H,GND. >> > The problem is they used one bit DACs for the R,G, and B. Really? Those converters "Mangelore" is talking about take most likely analog RGB, with analog RGB there is no point in having an "intensity" input. > If you find out that those DACs are more than 1 bit - then you can tie the > Intensity lines to the R,G & B DACs and voila - 16 colors. Just takes a few > wires. However, it is likely all integrated into a single chip and you would > have to look at the specs of the chip itself - if it has an Intensity input > pin and tie it there and voila. Those cheap ________, doesn't think about > that. As far as the DAC's are concerned; a couple of resistors suffice. It doesn't make sense to make an one or two bit DAC IC. Turning RGBI into analog RGB (with all 16 colors) requires no more than a few resistors. |