C=128 80Col NTSC Color.
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From: Brian Ketterling on 18 Mar 2007 02:40 "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. They're supposed to be CGA to VGA converters (see Christian Lott's post earlier in the thread), so they should take digital RGBI. I must have missed it on the website, though -- I didn't see anything about how many colors they output, or what kind of DACs they use. Brian --
From: Mangelore on 18 Mar 2007 03:16 Good news. Got it working. All 16 colours are now displayed in a perfect manner on my VGA screen! The solution was so simple it's laughable... My initial modification interfaced the Intensity signal directly into the RGB analog inputs of the surface mounted Analog Devices chip found on the ACV-011 board. There were a number of resistors and capacitors between the RGB TTL inputs and the analog inputs of the AD chip. While the 16 colours were all on the screen, the brightness was bleeding too much. So, I then interfaced the Intensity signal just after the first analog conversion stage with a few resistors and it worked like a charm. Cheers Fotios Rick Balkins wrote: > 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 > >
From: Mangelore on 18 Mar 2007 03:18 Hi Brian, They use an Analog Devices ad9985 chip. Cheers Fotios Brian Ketterling wrote: > "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. > > They're supposed to be CGA to VGA converters (see Christian Lott's post > earlier in the thread), so they should take digital RGBI. I must have > missed it on the website, though -- I didn't see anything about how many > colors they output, or what kind of DACs they use. > > Brian
From: Rick Balkins on 18 Mar 2007 15:36 Ok, I guess just a electronical matter and interference. Basically, in theory, my idea of tieing the Intensity to the R,G & B lines worked but have to do it after the first stage. Something funky but it works. Ok, this chip was designed for analog RGB input and basically scan doubling. Not digital. So, you would naturally convert the intensity to analog then tie it into the R,G, & B lines after the R,G & B had been converted to analog. Otherwise, you need to do it differently. The chip was designed for capturing ANALOG RGB and hooking them to digital flatpanel. In effect, the converter is doing the opposite. Converting analog RGB to a digital LCD panel. So what you should have done - is have three 2-Bit DACs (like used inside the DAC board in the 1902A), Basically each DAC has two digital inputs and 1 analog output. So, you would be tieing the Intensity line to the high-bit of each of the DACs for example and tie the Digital Red, Green & Blue lines from the CGA / VDC video output. Then convert to analog. You don't want to be mixing a digital intensity signal into an analog red, green or blue. Kind of gets messy. I think, that is what you had sort of an issue with. Same thing with Analog Intensity into digital inputs of the DACs. Gets messy as the Analog Intensity is not clean. In this case your resistor/capacitor circuit that makes each DAC circuit. You don't want to place an analog signal into a digital input. Whatever the case is, you would then have a clean conversion. In your case, you home-brewed your DAC circuit with resistors and capacitors, ect. With basically two digital inputs (bits-IN) and one analog out put. Basically three circuits. But you made a 4th "DAC" with the intensity and put it into a digital inputs of each of your "Red-DAC","Gree-DAC" and "Blue-DAC" circuits. Thus, getting a messy input. This is my theory on what you wrote. I'm probably scaring myself, now. "Mangelore" <fotios(a)commodore128.org> wrote in message news:cH5Lh.12819$8U4.11549(a)news-server.bigpond.net.au... > Good news. Got it working. All 16 colours are now displayed in a perfect > manner on my VGA screen! The solution was so simple it's laughable... My > initial modification interfaced the Intensity signal directly into the RGB > analog inputs of the surface mounted Analog Devices chip found on the > ACV-011 board. There were a number of resistors and capacitors between the > RGB TTL inputs and the analog inputs of the AD chip. While the 16 colours > were all on the screen, the brightness was bleeding too much. So, I then > interfaced the Intensity signal just after the first analog conversion > stage with a few resistors and it worked like a charm.
From: Mangelore on 18 Mar 2007 16:50
Yes, you're correct!... but also scaring me now :) Rick Balkins wrote: > In your case, > you home-brewed your DAC circuit with resistors and capacitors, ect. With > basically two digital inputs (bits-IN) and one analog out put. Basically > three circuits. But you made a 4th "DAC" with the intensity and put it into > a digital inputs of each of your "Red-DAC","Gree-DAC" and "Blue-DAC" > circuits. Thus, getting a messy input. This is my theory on what you wrote. > > I'm probably scaring myself, now. > |