Pokemon Roms that save inside the rom and not to the ram?

[chowder908]

So I recently got a hold of a reproduction of pokemon green. Turned out to just be a modified blue rom....
But after fiddling with the rom I dumped off the cartridge I found out my save was still intact even tho I didn't save using the emulator. If I try and save with an emulator it locks up, but it seems that my save file is saving in the rom itself and not to a sav file that would go in the ram because the cartridge I have doesn't have a save battery on it.

Does anyone know how this is done? I would like to rewrite a actual Green rom to this cart but since is had not save battery it won't save unless its's modified to save to the rom.

 

[ItsMetaKnight]

Can you create a IPS patch with Pokemon Blue as the original rom and your reproduction as the target rom? That way we can look at it without you having to upload Nintendo copyrighted content.
I think the tool is called Lunar IPS.

 

[Yepi69]

I think it saves to its flash memory, I used to have one of those cartridges when I was a kid and all I got was frustration since it kept deleting the save file weekly.

 

[chowder908]

Can you create a IPS patch with Pokemon Blue as the original rom and your reproduction as the target rom? That way we can look at it without you having to upload Nintendo copyrighted content.
I think the tool is called Lunar IPS.

Here is an IPS patch https://www.dropbox.com/s/wsdo9icp8i9t1dl/pk_green.ips?dl=1

The rom I used was Pokemon - Blue Version (UE) [!].gb The rom files seemed to match up when I was looking at them in Hex editor.

IF you can tell me how they pulled this off i'd really appreciate it so I can modify my own green rom to write to this cartridge.