Hello fellow SNES passionate people,
I am currently studying the SNES PPU and staring at the gorgeous schematics by Jonathon W. Donaldson (https://wiki.superfamicom.org/uploads/s ... _color.pdf).
I can make sense of almost everything except for the shared VA14 line. The PPU1 has dedicated address lines for each VRAM chip, labeled [VAA0-VAA13] and [VAB0-VAB13]. This wiring provides the ability to fetch two different bytes when Mode 7 makes tile data access non-linear. So far so good.
But why is there not VAA14 and VAB14? Instead, I see a shared line VA14. I looked at nocash specs (https://problemkaputt.de/fullsnes.txt) and read this:
Moreover, I found this text in SNES Developent Wifi (https://wiki.superfamicom.org/backgroun ... ress%20bus).
But I wonder if this description is wrong.
With a single VA14 line, the even bytes are in the lower (0-16KiB) part of a chip. And the odd bytes are in the upper part (16-32KiB) of a chip. If that was to be correct interpretation, then the single VA14 would make sense. Do I understand it correctly?
I am currently studying the SNES PPU and staring at the gorgeous schematics by Jonathon W. Donaldson (https://wiki.superfamicom.org/uploads/s ... _color.pdf).
I can make sense of almost everything except for the shared VA14 line. The PPU1 has dedicated address lines for each VRAM chip, labeled [VAA0-VAA13] and [VAB0-VAB13]. This wiring provides the ability to fetch two different bytes when Mode 7 makes tile data access non-linear. So far so good.
But why is there not VAA14 and VAB14? Instead, I see a shared line VA14. I looked at nocash specs (https://problemkaputt.de/fullsnes.txt) and read this:
Code:
47 SRAM VA14 (sram address bus for upper/lower 8bit data)Code:
note that in hardware, VRAM is set up such that odd bytes are in one RAM chip and even in another, and each RAM chip has a separate address busWith a single VA14 line, the even bytes are in the lower (0-16KiB) part of a chip. And the odd bytes are in the upper part (16-32KiB) of a chip. If that was to be correct interpretation, then the single VA14 would make sense. Do I understand it correctly?
Statistics: Posted by fabiensanglard — Thu Aug 01, 2024 2:47 pm — Replies 4 — Views 196