Display timing: Difference between revisions

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[[File:disp.png|right|frame]]
=Pixel dimensions=
In NTSC mode, the display is 320x224 pixels. In PAL mode, it is 320x256 pixels.


Upper 9 bits of register {{Reg|REG_LSPCMODE}}:
* NTSC: 384 * 264 pixels.
*$00F8-$00FF : Vertical sync (8)
* PAL: 384 * 312 pixels.
*$0100-$010F : Top border (16)
 
*$0110-$01EF : Active display (224)
See [[frame size]] for the '''active''' display size.
*$01F0-$01FF : Bottom border (16)
 
=Sync=
 
'''mclk''' refers to the 24MHz master [[clock]]. A pixel lasts 4 mclk.
 
Notes: After /RESET goes high, SYNC goes high after 1399 mclk.
 
[[File:Sync_timing.png|1024px]]
 
{{Sig|CHBL|CHBL}} is the horizontal blanking signal, it tells {{Chipname|NEO-B1}} to output color 0 of [[palettes|palette]] 0, which is the [[palettes|reference color]].
 
{{Sig|BNKB|BNKB}} is the vertical blanking signal, it forces the [[video DAC]] inputs to 0.
 
==Horizontal==


From mvstech.txt (by Charles MacDonald):
[[File:Timing_video_lines.png]]
<pre>
[[File:Timing_video_hblank.png]]
Measured in reference to main 24 MHz clock (mclk):


Horizontal timing
* 112 mclks (28px) horizontal sync pulse
* 112 mclks (28px) back porch
* 1280 mclks (320px) active display
* 32 mclks (8px) front porch


Pulse widths:                                 
* 32 + 112 + 112 = 256 mclks (64px) horizontal blanking
  111 mclks horizontal sync                    27.75 pixels
* 32 + 112 + 112 + 1280 = 1536 mclks (384px) total per scanline
  256 mclks horizontal blanking                   64 pixels
1280 mclks active display                      320 pixels
1536 mclks per scanline                         384 pixels


State to state timing:
[[File:Timing_video_vblank.png]]
  118 mclks /HSYNC rising to /HBLANK rising    29.5 pixels (left border)
1280 mclks /HBLANK rising to /HBLANK falling    320 pixels (display)
  27 mclks /HBLANK falling to /HSYNC falling  6.75 pixels (right border)
  111 mclks /HSYNC falling to /HSYNC rising    27.75 pixels (horizontal sync)


384 pixels per scanline: (rounding up)
BNKB (blanking to 0V) changes state 14px after H-sync (middle of the back porch)


  28 pixels horizontal sync pulse width
==Vertical==
  29 pixels /HSYNC low to /HBLANK high
320 pixels /HBLANK high to /HBLANK low
  7 pixels /HBLANK low to /HSYNC low


Vertical timing
Corrected from and added on from mvstech.txt (by Charles MacDonald).


264 scanlines per frame:
There are 264 scanlines per frame:
* 8 scanlines vertical sync pulse
* 16 scanlines top border (active in PAL, blanked in NTSC)
* 224 scanlines active display
* 16 scanlines bottom border (active in PAL, blanked in NTSC)


  8 scanlines vertical sync pulse
Upper 9 bits of register {{Reg|REG_LSPCMODE}}:
  16 scanlines top border
* $0F8~$0FF : Vertical sync (8px)
224 scanlines active display
* $100~$10F : Top border (16px)
  16 scanlines bottom border
* $110~$1EF : Active display (224px)
* $1F0~$1FF : Bottom border (16px)


Frame timing
=Frame timing=


Frame rate is 6 MHz / 384 / 264 = 59.18 Hz.
See [[framerate]].
</pre>


[[Category:Video system]]
[[Category:Video system]]

Latest revision as of 12:59, 6 February 2018

Pixel dimensions

  • NTSC: 384 * 264 pixels.
  • PAL: 384 * 312 pixels.

See frame size for the active display size.

Sync

mclk refers to the 24MHz master clock. A pixel lasts 4 mclk.

Notes: After /RESET goes high, SYNC goes high after 1399 mclk.

CHBL is the horizontal blanking signal, it tells NEO-B1 to output color 0 of palette 0, which is the reference color.

BNKB is the vertical blanking signal, it forces the video DAC inputs to 0.

Horizontal

  • 112 mclks (28px) horizontal sync pulse
  • 112 mclks (28px) back porch
  • 1280 mclks (320px) active display
  • 32 mclks (8px) front porch
  • 32 + 112 + 112 = 256 mclks (64px) horizontal blanking
  • 32 + 112 + 112 + 1280 = 1536 mclks (384px) total per scanline

BNKB (blanking to 0V) changes state 14px after H-sync (middle of the back porch)

Vertical

Corrected from and added on from mvstech.txt (by Charles MacDonald).

There are 264 scanlines per frame:

  • 8 scanlines vertical sync pulse
  • 16 scanlines top border (active in PAL, blanked in NTSC)
  • 224 scanlines active display
  • 16 scanlines bottom border (active in PAL, blanked in NTSC)

Upper 9 bits of register REG_LSPCMODE:

  • $0F8~$0FF : Vertical sync (8px)
  • $100~$10F : Top border (16px)
  • $110~$1EF : Active display (224px)
  • $1F0~$1FF : Bottom border (16px)

Frame timing

See framerate.

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