From: KC5TJA <kc5tja@topaz.axisinternet.com>
  To  : ggi-develop@eskimo.com
  Date: Wed, 26 Aug 1998 12:28:07 -0700 (PDT)

Re: Matrox cards and Sync on green

On Wed, 26 Aug 1998, Isaac Connor wrote:

> > What is sync-on-green? Is both horizontal and vertical sync
> > encoded into the green signal? If so, could I hook up my Millennium
> > card to a monochrome monitor that wants a composite signal?
> > (provided the card can produce correct timings ofcourse)

Perhaps -- perhaps not.  This depends on whether or not the sync signal on
the green line adheres to the monitor's expectations of the sync signal.
Does it have a front porch?  A back porch?  If so, are they required to be
"blacker than black", or just at black level?  etc.

> Sync-on-green is have bothh sync signals on the green wire.  Um, composite
> sync has them embedded on a separate wire...I would ASSUME that the

To the best of my knowledge (gained from working on the TV repair industry
for some years):

Composite sync, a term first used to describe NTSC, means that
the sync is embedded in the luminance signal of the video stream, and
requires extensive analog electronics to encode and decode it.
Consequently, it tends ot be analog in nature.

Also note that Composite sync requires 8 cycles of 3.579545MHz subcarrier
to be embedded in the back porch of every horizontal sync pulse, for NTSC. 
The phase of this reference "color burst" signal determines the "tint" for
that line.  As you might guess, the TV's "tint" control merely adjusts the
phase of an internal PLL circuit, which locks onto the received color
burst frequency.  This gives an adjustment for all colors on the screen. 

Sync-on-green is a more-or-less "digital" version of composite sync.  It
forces the green signal to 0V during sync, but does not have any front or
back porches, though it MAY have equalizing pulses.  In this system,
"black" level may be as high as 0.5V to 1V.

VGA, fixed frequency, or multi-sync syncing using has the sync pulses on
separate data lines.

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