Super Famicom letterbox borders general knowledge question

[Skykid]

Does anyone know the technical reason why some SFC games have letterbox borders top and bottom even thought they're all running 60hz NTSC?

For example, Undercover Cops has borders, Xmen Mutant Apocalypse doesn't. Sometimes the letterbox size seems to differ too.

Just curious, thanks for the help.

[trap15]

I believe that those particular games turn off the display hardware at the "end" of a screen and turn it back on at the beginning, causing the black borders. The reason for doing this is that it allows access to the VRAM to be much, much faster than if the display was on during those lines. It uses the extra time for uploading more data to the VRAM.

[Skykid]

I believe that those particular games turn off the display hardware at the "end" of a screen and turn it back on at the beginning, causing the black borders. The reason for doing this is that it allows access to the VRAM to be much, much faster than if the display was on during those lines. It uses the extra time for uploading more data to the VRAM.

Thanks dude! Would you mind explaining that in idiot terms for me? Is it something to do with processing speed? For example, the question came up while we were gawping over the quality of the Undercover Cops port in disbelief and it was suggested the borders meant fewer lines were being drawn = less information = quicker processing of large amounts of animation and multiple on-screen sprites.

Is it something like that?

[trap15]

Partly. The thing about the VRAM in the SNES/SFC is that only one "device" can access it at a time: the CPU, or the PPU (Picture Processing Unit). So when both the PPU and CPU want to access it, the CPU gets stalled until the PPU is done. The CPU is "noncritical" in that if it waits, nothing will break; but the PPU has to keep going at a set rate, or the picture will be messed up.

By turning off the display, the PPU will stop reading from VRAM (since it doesn't need to access it anymore), so the CPU gets full reign over the VRAM. This happens normally as well during VBlank and HBlank time. Some games may need more time than what these blanking periods allot for, so they turn off the display early and turn it on later to give some more time. For example, to upload new animation frames, or update background tiles.

[Skykid]

And that's in idiot terms?

I think I get it. Basically less on screen display frees up more CPU access for the VRAM which ensure the graphics don't glitch or corrupt?

Does it correlate letterboxing would appear on more CPU/graphics intensive games than those with less to process (or in some cases, a shortcut for poor programmers to keep things smooth?)

[trap15]

Heh, sorry, I don't want to make any misconceptions or miss any relevant detail.

Basically less on screen display frees up more CPU access for the VRAM which ensure the graphics don't glitch or corrupt?

Almost right. It's not a matter of corruption, it's a matter of letting the CPU upload more data in less time. Though it does follow that it also means no corruption!

Does it correlate letterboxing would appear on more CPU/graphics intensive games than those with less to process (or in some cases, a shortcut for poor programmers to keep things smooth?)

Yes, precisely.

[Skykid]

Cool stuff! :thumbsup"