Re: Apple RGB monitor- VGA interface

[aw133@lafn.org (James Poore)]

In a previous article, rubywand@swbell.net (Rubywand) says:

>Scott G. writes ...
>
>> .... I searched the net and found dozens of
>> companies that make little devices that will take a 30kHz
>> (VGA/SVGA) output and transform it to 15kHz for connection
>> to "TV" analog RGB devices (NTSC rate).  These typically
>> sell for $25 and are designed to connect PC and Mac computers
>> to projection displays.
>> 
>> If such a device is possible for so little money, would it
>> not be possible to build the reverse device?  One that would
>> take analog RGB output from a GS or an Amiga and pipe it to
>> a VGA/SVGA/Mac monitor?  There is an market for such a thing.
>> It would be different from the Second Sight too, because it
>> will allow the display of ALL of the GS's modes ....
>>
>
>     For sure, there would be a market if the device could be priced
>below $75. The interface plus a VGA/SVGA monitor could become the
>standard GS monitor setup.
>
>     The main challenge is finding a way to double the dot rate. This
>would seem to require capturing at least each horizontal line and
>resending it. Basically, I guess, you would read-in the first (top) line
>to Buffer-A during the monitor Vertical Blanking period and, afterward,
>send it twice while loading in the next line to Buffer-B. You, then send
>Buffer-B twice while loading Buffer-A, etc..
>
>     An alternative is to just capture and re-send whole screens. You
>would need more buffer memory; but, the design could be easier because
>timing would be less critical.
>
>     Either approach could display the usual 200-line GS screen as 400
>lines on a 30KHz VGA/SVGA monitor. It should look very nice and, as you
>mention, all GS display modes would be available.
>
>     Of course, once you've gone to the trouble of developing such an
>interface, there would be a temptation to add embellishments (e.g. a way
>to display 400 unique lines, more colors, etc.).  It would not be too
>surprising to discover that Second Sight began as a 'simple' VGA monitor
>interface. 
>
>     In quantities of a thousand or so, the basic GS-to-VGA monitor
>interface circuit might be commercially doable at a sale price below
>$75, especially, if it's an Apple club project or other such situation
>where no one actually expects to be paid much for the time he/she
>contributes.

Nothing will be gained by just doubling the scan rate to 30Khz.  You will 
still have 320 or 640 horiz pixels on the screen just doing it faster.

Jim

-- 
James M (Jim) Poore--Apple II's Forever--Especially IIgs's
Los Angeles Free Net---aw133@lafn.org
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Where is that damn SIG?