C=128 80Col NTSC Color.
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From: Mangelore on 17 Mar 2007 18:00 Rick Balkins wrote: > 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. > Hi Rick, The converter board I have uses a surface mounted Analog Devices chip with only RGB inputs. I've tried wiring up the Intensity line using a few resistors and wires directly to the RGB inputs of chip but the results are poor. While it does now output 16 colours to the screen, there's significant levels of brightness bleeding across the screen at times. I've also tried using a few diodes without luck. Cheers Fotios
From: Tom Lake on 17 Mar 2007 18:17 > 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. IBM's first color card in 1981 always had 16 colors available in text mode (I still have one) In graphics mode, there ware two palettes of four colors each available. There was also a hidden mode that allowed 16 colors in 160 x 200 resolution but it wasn't supported by BASIC so wasn't used widely. Tom Lake
From: Rick Balkins on 18 Mar 2007 00:54 I think there was a few cheap CGA cards that didn't do all 16 colors. Probably a screwed up CGA card. All of mine, does all 16 colors. In theory, I can extend it by adding more bit lines from elsewhere to a DAC board that would make CGA. I might try it out sometime with the C= PC-10 of mine. Afterwards, I'll work the scan-doubling. I could use 8-bit DACs. Which would be impressive, extending of the palette capacity. As for why a CGA2VGA converter wouldn't support all 16 colors. As for any program, usually only 8 colors are displayed at a time so maybe it would be necassary to test the converter with a program that displays all 16 colors. As for VDC, that exactly does such in most programs. Oh well. "Tom Lake" <tlake(a)twcny.rr.com> wrote in message news:45fc68f9$0$17177$4c368faf(a)roadrunner.com... >> 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. > > IBM's first color card in 1981 always had 16 colors available in text mode > (I still have one) In graphics mode, there ware two palettes of four > colors > each available. There was also a hidden mode that allowed 16 colors in > 160 x 200 resolution but it wasn't supported by BASIC so wasn't used > widely. > > Tom Lake >
From: Rick Balkins on 18 Mar 2007 01:07 What is the difference between RGBI (Digital RGB) and RGB... well every time you hook a C= or CGA/EGA card to a CGA/RGBI monitor, it is already doing what I suggested inside the monitor. There is a DAC board in the monitor that converts your RGBI into analog RGB. RGBI is nothing more then a 4 bit parallel bus and is useless to the monitor until it is converted to analog. Basically the DAC board is a set of three 2-Bit DACs and the Intensity line is tied to all three DACs. Intensity is used to give a second intensity level for R,G,B but not independently unless you add two more "Intensity" lines from elsewhere. Which isn't there built into the VDC or CGA card but you could in theory fake it by adding into the bus from a data bus. Since from a technical sense, they are just bits to be converted to real color. Digital R,G & B lines are just bits not color. It is only color after converted to analog AND sent out the raster gun or however the LCD works. "Patrick de Zeester" <invalid(a)invalid.invalid> wrote in message news:45fc251f$0$13343$e4fe514c(a)dreader16.news.xs4all.nl... > 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.
From: Rick Balkins on 18 Mar 2007 01:11
You're better off making your own DAC board and scan doubler. Or find a chip that does support intensity input. However, can you provide me the chip's number (like MOS 6502 for the CPU of the C=) There maybe is an actual Intensity line. I need more specifics. "Mangelore" <fotios(a)commodore128.org> wrote in message news:hyZKh.12437$8U4.9753(a)news-server.bigpond.net.au... > Rick Balkins wrote: >> 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. >> > > Hi Rick, > > The converter board I have uses a surface mounted Analog Devices chip with > only RGB inputs. I've tried wiring up the Intensity line using a few > resistors and wires directly to the RGB inputs of chip but the results are > poor. While it does now output 16 colours to the screen, there's > significant levels of brightness bleeding across the screen at times. I've > also tried using a few diodes without luck. > > Cheers > Fotios |