My calculations suggest it's worth it even if not using much of the extra 2MB space - 1280x1024x16bit can be done in 2.5MB for example, which would be a useful bump in resolution and match some of my LCDs precisely.I don't know if 4MB is worth doing, it seems like VRAM bandwidth might prevent any real increase in bit depth or resolution.
But having got in to the detail of this, progressed a design to use 16bit RAMs (KM4216C258G) for 2MB, and now looking at 4MB -- I'm struggling to figure how I can arrange eight of the 256Kx16bit RAMs because the serial (VIDC) side needs to read 64bits continuously. Best I can conceive is something like a flip/flop on the serial clock so every alternate 64bits is from different quads of 16bit RAMs, then arrange the DRAM side to have an interleave every 64bits, but not sure best/if/how to do that. Move all the address bits down by 1 and use the bottom address as some kind of mask for Oe/We? But then QSF needs ORing between two RAMs in each rank maybe. Ugh I'm confused. Better to try and see if there are such things as 512Kx16 VRAMs?
Statistics: Posted by IanJeffray — Sat Feb 01, 2025 11:44 pm