Re: [stella] tutorial progress

Subject: Re: [stella] tutorial progress
From: Chris Wilkson <ecwilkso@xxxxxxx>
Date: Fri, 28 Jun 2002 16:33:42 -0400 (EDT)
On Fri, 28 Jun 2002, Erik Mooney wrote:

> Actually, IIRC from Video Demystified, it's VSYNC that's "blacker than
> black", a signal at much lower voltage than regular black.  VBLANK
> shows up on a TV the same as writing 0 to COLUBK and urning off
> any objects/playfield.  (Try it in the middle of a frame.)

The blanking level is suppposed to be "blacker than black".  And the sync
level is even blacker.   It's "blacker than blacker-than-black".  If I were
to draw a "proper" greyscale stair step on a given scanline, starting with
black, jumping to white and stepping back down to black, the brightness
would look like:

                   |   ---
                   |      ---
                   |         ---
                   |            ---
                   |               ---
                   |                  ---
______    ______---                      ---______    ______
      |  |                                        |  |
      |__|                                        |__|

                |                           |
   h   h    h   | b  w  g  g  g  g  g  g  b | h    h    h
   b   s    b   | l  h  r  r  r  r  r  r  l | b    s    b
   l   y    l   | a  i  a  a  a  a  a  a  a | l    y    l
   a   n    a   | c  t  y  y  y  y  y  y  c | a    n    a
   n   c    n   | k  e                    k | n    c    n
   k        k   |                           | k         k
                |     visible line          |

Notice that black is actually above the blanking level.  This is in the
original NTSC spec.  And it is implemented on some 2600 motherboards, by
using the /BLANK pin.  On other motherboards, this pin is left out of the
circuit, so black is the same as blank.  In all cases, sync is far below
blanking level.


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