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VDP2 Display
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The VDP2 generates the following types of displays:
NTSC - 60 frames per second, 263 lines per frame
PAL - 50 frames per second, 313 lines per frame
Here's a description of how each frame is composed. I have visually
inspected the NTSC displays and provide more details about them, whereas
for the PAL modes I can only divide the display into the active display
and blanking/border/sync areas.
NTSC, 224 lines:
224 lines for the active display area
8 lines for the bottom border area
5 lines for the bottom blanking area
3 lines for the vertical sync area
15 lines for the top blanking area
8 lines for the top border area
NTSC, 240 lines:
240 lines for the active display area
5 lines for the bottom blanking area
3 lines for the vertical sync area
15 lines for the top blanking area
PAL, 224 lines:
224 lines for the active display area
32 lines for the bottom border area
25 lines for blanking and sync
32 lines for the top border area
PAL, 240 lines:
240 lines for the active display area
24 lines for the bottom border area
25 lines for blanking and sync
24 lines for the top border area
PAL, 256 lines:
256 lines for the active display area
16 lines for the bottom border area
25 lines for blanking and sync
16 lines for the top border area
A typical display frame looks like this:
+----------------+ Scanline 0
| |
| Active display | Graphics data is shown here.
| |
+----------------+
| | Either black (BDCLMD=0) or set to the border color
| Bottom border | as defined by the back screen. The bottom border is
| | optional.
+----------------+
| |
| Bottom blanking| Appears as light black.
| |
+----------------+
| |
| Vertical sync | Appears as pure black.
| |
+----------------+
| |
| Top blanking | Appears as light black.
| |
+----------------+
| | Either black (BDCLMD=0) or set to the border color
| Top border | as defined by the back screen. The top border is
| | optional.
| |
+----------------+ Scanline 262 or 313
Exclusive Monitor display modes
When bit 2 of the HRESOx field is set, the exclusive monitor modes are
enabled. It's not exactly clear what kind of monitor these modes are
supposed to be used with, I would guess HDTV or possibly VGA.
Depending on the screen width, the following types of displays are
generated:
320 or 640 pixels: (31kHz monitor)
480 active display lines
45 VBlank lines
525 lines total
352 or 704 pixels: (Hi-Vision monitor)
479 active display lines
82 VBlank lines
561 lines total
These display settings are identical between a NTSC and PAL Saturn.
The VRESOx bits have no effect on the display size.
It seems that while the LSMDx bits will enable an interlaced display,
this is not required for the exclusive monitor modes. I would guess that
enabling interlacing might adversely affect the display. The VDP2 manual
recommends turning interlacing off entirely.