Re: IIe Analog RGB - rare, unpopular, both?

["Michael J. Mahon" <mjmahon@aol.com>]

pitz wrote:
> I recently sold off my Apple IIe to someone who will probably use it
> more often than I would (since I use my IIgs more than the rest of my
> Apple II stuff).
>
> Included with what I sold is a Taxan RGB card.  There's not a lot of
> information I could find, but from what I gather, it is one of the few
> analog RGB cards for the Apple IIe.  There was a mention of Applied
> Engineering having two different ColorLink daughterboards (one analog
> RGB and one digital RGB) for their RamWorks card.  There is that
> document from Marco Orlandi that describes how to wire up the digital
> RGB card from Apple (Apple 80col/RGB card) to generate an analog RGB
> output.  And then there are the Taxan cards.  And the Second Sight
> cards.

RGB cards were not particularly popular for the Apple II because they,
plus the RGB monitor, were *very* expensive.

Most people already had a color TV, so Apple II color displays were
usually composite video to a color TV--with or without an RF modulator
in between.

Since 80-column text is not practical with composite color, many users
also had a monochrome monitor connected to the composite video, so that
text displays were crisp.  This type of setup was much less expensive
and produced a superior text (and monochrome graphics) display, since
monochrome monitors are not hobbled by the dot pitch of a shadow mask
(which was rather coarse in the color CRTs of the time).

> I've read that a lot of games were developed with the composite video
> output in mind, so using RGB is not a lot better.  I did try to run a
> program (II Write) a few weeks back and the difference was very
> evident.  I am not certain what resolution it used, but RGB output did
> not exhibit the ghosting effects evident in composite output, and the
> text in the menu bar was very sharp.

The absence of color "aliasing" is the primary benefit of RGB monitors
(and also their biggest drawback when used to display graphics designed
to benefit from aliasing).

> Why hadn't Apple made an analog RGB card for the IIe, noting that they
> chose to have the IIgs generate analog RGB output from its video
> port?  Is there a difference in quality between digital and analog
> RGB?

Since the Apple II video system is only capable of directly representing
6 colors (including black and white ;-), and all RGB cards simply
"presented" that small pallette, having an "analog" output is somewhat
beside the point (as long as the "digital" monitor presented colors
relatively faithful to the purple/green/blue/orange expected of an
Apple II.

"Analog" and "digital" as applied to monitors, refers to the levels
of the input signals, with "digital" usually meaning TTL levels with
only (approximately) 0v and (approximately) 5v valid, and "analog"
usually meaning any voltage from 0v-1v, with the color displayed
proportionally to the voltage.

In fact, many "digital" monitors were actually analog monitors with
level-converting circuits, so they would respond proportionally to
voltages *between* 0v and 5v, though not advertised to do so.

-michael

NadaPong: Network game demo for Apple II computers!
Home page:  http://members.aol.com/MJMahon/

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