Endian-ness of 16bit SNES ROMs

Hi guys,

I am trying to make some SA-1 and SDD-1 repros using M27c322 EPROMs with the adapters from @TheRealPhoenix found in this thread. I am burning the EPROMs using an adapter for my TL866 that I built using the schematic from this thread.

The only question I have is, what is the endianness that the SNES uses for these 16bit cartridges? Can I simply burn my Super Mario RPG (for example) ROM onto my M27c322 with my TL866 without any byte-swapping?

I'm really struggling to find a definitive answer in an existing thread on this one, so any help from someone who has done this before would be appreciated. The TL866 software seems to show the ROM data byte-swapped in it's window, which is also a little confusing...

 

There's no byte swapping required

 

OK thanks

Am I right in saying, though, that you do need to byte-swap for Mega Drive games? (I read this somewhere on a forum)

 

Yes, assuming it's not already swapped.

If your software shows the buffer in 8 bit and 16 bit and the 16 bit looks swapped compared to 8 (this is how my programmer works).

You should be able to load a rom and be able to read the text in 16 bit mode but not 8.

 

Yes that's how my programmer (TL866) works, too. Can Mega Drive ROMs come in both swapped or non-swapped states? I guess it's wise then to always check the ROM in a hex editor before doing anything.

 

Just open in your programmer software, switch to 16 bit mode. See if you can read the text or not.

 

No need to byte-swapp with my SA-1/SDD1 adpaters: they are straight-forward as possible.

 

It's not specific to your adapter. There's no byte swapping of snes roms.

 

If you're using a 27C801 to directly replace a maskrom, you can use SNES ROM UTILITY and byteswap the file before burning it: this will make the output closer to the orginal pinout of an actual Maskrom, minus the A16 and /OE to manualy wire. This is to avoid a spaghetti mode.

But if you're using 29F016/29F032 on a TSOP/DIP adpater yes, no byteswap.

 

Thats not byte swapping for endianness (reversing the order the 2 bytes), thats selectively pin swapping to make the rom pinout better, as you said.

This is byte swapping:



To byte swap with wiring - you would need to wire D0-7 to D8-15 and D8-15 to D0-7.

You are confusing 2 things.