Is force blank also HBlank??? if not, when does it happen??
If you mean disabling BG and Sprites for "Force Blanking", this is not the same as HBlank. HBlank would be considered the very brief time after a scanline is rendered and before it begins rendering the next line. It takes 256 PPU cycles to render the line. Other cycles prepare and fetch certain data related to drawing. I'm sure someone else can give a more detailed explanation.
The only use of HBLANK usually is to update scroll and nametable registers to achieve raster effects like for a status bar or parallax effects.
The term "forced blanking" is usually used to describe a technique where the programmer forces rendering to be disabled during times when the PPU would normally be rendering the picture. This is often used to free the PPU for VRAM accesses, because it can't be accessed while the picture is rendering. It's usually done right before (at the bottom of the screen) or right after (at the top of the screen) the vertical blank, so that its duration is effectively increased.
HBlank is much shorter than VBlank, and for timing reasons it would be very difficult and unpractical to extend it with forced blanking. The blanked areas at the left and/or the right of the screen would jitter a lot and there wouldn't be much CPU time left for doing other things (such as game logic). Also, enabling and disabling rendering that fast would probably screw up the sprites.
do you guys know any documents about this? so I can read about the details.
thanks for the reply