Talk:PPU pinout

EXT port description

Can the function of the EXT pins be described more precisely? I do not understand very well, there are four EXT pins, and the colors are six bits (selecting the palette entry is only two bits), so how can it decide the color from this? --Zzo38 (talk) 00:27, 21 January 2013 (MST)

I am having a doozy of a time figuring out how to rephrase it on the main page in an intelligible manner, so I'll just start from scratch: Assume the NES's palette has no gaps and thus is a {32 entry} × {6 bit} array. log₂(32)=5, so indexing this array requires 5 bits. The EXT port takes as input or output the bottom 4 bits of this 5 bit index. If the EXT port is used as an input, it replaces the "transparent" color in index 0 with any of colors 0-15, i.e. it's an extra layer of background and background-colored sprites underneath. —Lidnariq (talk) 01:59, 21 January 2013 (MST)