BigEd wrote:
You'll usually have RAM wider than one bit, which feeds a shift register. So you don't need a 25MHz access, perhaps more like 1/8 or 1/16 of that. Unless your pixels need more than one bit - but it's still the case that you can build a memory 32 bits wide.
This ^^^ you'll be doing byte reads, so the ram address will be incrementing every ~320ns which means just about any RAM will do
If you do 8bpp color you will of course need something with less than 40ns access time.
Video access happen with a constantly incrementing address and if you give exclusive access to the video hardware for the duration of a visible frame you will be able to keep the RAM selected and keep /OE asserted for the full frame which means you only need to worry about tAA (aka Address to Data Valid)