Super Metroid is LoRom, but uses A15??

bazz · Post by **bazz** » Mon Sep 19, 2011 3:50 am

I don't get it... Isn't that what LoRom is all about, neglecting A15?
http://www.snescentral.com/pcb.php?id=0 ... side=front

First thing I thought was that it is Fast ROM so it must be using the extra banks at the end for 32Mbit.. But you can see on the cart that A23 is Not Connected, soo... wTF? Isn't this really A hirom game??

bazz · Post by **bazz** » Mon Sep 19, 2011 3:58 am

o.m.g it's for the MAD-1 .. ok got it

but 32 mb on lorom? how? This is truly "mixed" lorom+hirom correct?? why not just hirom??? They must be accessing lower half of banks $40 upwards. well really $C0 upwards cause its fastrom..

kyuusaku · Post by **kyuusaku** » Mon Sep 19, 2011 6:55 am

32M on LoROM is easy:

ROM A0-A14 = CPU A0-14
ROM A15-21 = CPU A16-22

Since there are 24 address lines you could even have a 64M LoROM game, but you wouldn't be able to use 64 KiB in banks $7E-7F IIRC due to WRAM mapping and only half the ROM could be accessed as FastROM.

I'm not sure if mixed LoROM/HiROM is used on any games, but it's only necessary when you have a game over 32M and you want all code to run FastROM. Perhaps Tales of Phantasia does it. Basically in that configuration a 32M ROM is wired as HiROM, a <=32M as LoROM, then the decoder selects them based on A22.

bazz · Post by **bazz** » Mon Sep 19, 2011 10:57 am

Post by **tepples** » Mon Sep 19, 2011 10:59 am

Skipping A15 is how LoROM is defined, so I'd say all.

bazz · Post by **bazz** » Mon Sep 19, 2011 11:01 am

thanks tepples.. ^_^