[Coco] again: CoCo RGB to VGA conversion

[jdaggett at gate.net]

Mark

I understand where you are coming from. Any attempt to go to a 31 KHz sync 
frequency as an add on circuit will require a lot of work. 

Scan doubling itself is not difficult. Two approaches come to mind, first is to digitize 
the 15KHz analog and store the data in a large FIFO or dual port ram. This  has a 
distinct problem in that you ar eemptying the bucket faster than y ou can fill it. The  
only real decent  method is to double samle the 15KHz analog signal and store it in 
a FIFO or Dual port ram and have the 31KHz scan section take every other byte out 
when generating the 31Khz analog signal. 

Still any attempt to digitize the analog signal from the Coco then convert it back to 
analog will loose some signal quality. This a nice add on feature and gets around a 
problem. Still you have 64 bit color on a more modern monitor. 

james

On 18 Aug 2004 at 12:44, mmarlett at isd.net wrote:

From:           	mmarlett at isd.net
To:             	coco at maltedmedia.com
Date sent:      	Wed, 18 Aug 2004 12:44:06 -0500
Subject:        	Re: [Coco] again: CoCo RGB to VGA conversion
Send reply to:  	mmarlett at isd.net,
	CoCoList for Color Computer Enthusiasts 
<coco at maltedmedia.com>
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> james,
> 
> Since I did the research and it is common knowledge that most, not
> all, monitors start their hsync freq ~31 khz and up today.
> 
> I looked at various solutions and have come to the same conclusion as
> Torsten. More than what the CoCo really needs. A lower cost solution
> could be produced. Again this is just prelim leg work all looks great
> on paper. My design will be in a CPLD with external support
> circuitry.I will not start another design until the SuperBoard and
> Ethernet is completed.
> 
> Mark
> Cloud-9
> 
> 
> >Mark
> >
> >One major problem is that most modern monitors now will not do 15 KHz
> > horizontal sync any more. I did come across a LCD monitor that did.
> >
> >The AL 875 chip is the more promising of the lot. My only concern is
> >that
> an 
> >8 bit ADC has only about 50  dB signal to noise ratio. While there
> literally 16 
> >milion colors, not all will look well. In reality many of the darker
> colors and 
> >hues will not be accurate due to potential noise issues. Secondary
> >issues are that the input signal must stay within the range of the
> >ADC. Thespeed
> of 
> >the ADC is  not a m ajor issue today as there are plenty of good
> >quality ADC that  have sufficient speed for video. 
> >
> >james
> >
> >On 17 Aug 2004 at 21:23, Mark Marlette wrote:
> >
> >Date sent:      	Tue, 17 Aug 2004 21:23:18 -0500
> >To:             	CoCoList for Color Computer Enthusiasts 
> ><coco at maltedmedia.com>
> >From:           	Mark Marlette <mmarlett at isd.net>
> >Subject:        	Re: [Coco] again: CoCo RGB to VGA conversion
> >Send reply to:  	CoCoList for Color Computer Enthusiasts 
> ><coco at maltedmedia.com>
> >	<mailto:coco-
> >request at maltedmedia.com?subject=unsubscribe>
> >	<mailto:coco-
> >request at maltedmedia.com?subject=subscribe>
> >
> >> At 8/18/2004 04:11 AM +0200, you wrote:
> >> 
> >> Torsten,
> >> 
> >> I have done research on this project and it is in queue. SuperBoard
> >> will be finished before this is ever started though.
> >> 
> >> Mark
> >> Cloud-9
> >> 
> >> 
> >> >I'm still thinking about that task. This is for all you hardware
> >> >guys out there: Do you think it's possible to build a hardware for
> >> >CoCo RGB to VGA conversion out of these components:
> >> >
> >> >For 3-channel analog RGB -> digital RGB888 ADC:
> >> >
> >> >http://www.averlogic.com/password/AL875_Data_Sheets.PDF
> >> >
> >> >For digital RGB565 -> analog VGA conversion:
> >> >
> >> >http://www.averlogic.com/password/AL250_251_Data_Sheets.PDF
> >> >
> >> >Here's a design example:
> >> >
> >> >http://www.2k1.co.uk/products/averlogic/www1/AL250/AL875_250.pdf
> >> >
> >> >taken from this site which has more info:
> >> >
> >> >http://www.2k1.co.uk/products/averlogic/www1/AL250/
> >> >
> >> >Any comments welcomed.
> >> >
> >> >Torsten
> >> >
> >> >
> >> >--
> >> >Coco mailing list
> >> >Coco at maltedmedia.com
> >> >http://five.pairlist.net/mailman/listinfo/coco
> >> 
> >> 
> >> 
> >> -- 
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> >
> >
> >
> >-- 
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