Saturn carts ROM size / ROM dumping

[Madroms]

What could be considered as the correct size for the data found in the ROM of the Sega Saturn carts ?

As I am a novice in all the ROM stuff, I don't know which size to take.

Here is an example:

Let's take the Satellite cart.

It has 3 chips:

1) PALCE16V8H-10 - P8/4 9450AXA/L - AST94237620-001A - 20 pins=> probably CMOS

2) 27C256-20 - 8831 HKB - PGM@12.5V - 28 pins => probably 256K (32K x 8) CMOS EPROM

3) M27256-25F1 - ST9022 - 6212424 - A40360 - 188 116 - 28 pins => probably NMOS 256K 32K x 8 UV EPROM

The data is contained by the chip 2) and/or 3) (as I said, I am a novice), both are 256K chips.

Ok.

On the other side, by checking the memory of the saturn when the satellite is inserted, you can see that the data of the satellite is 64K long, mirrored 8 times (total = 512K).

So, what could be considered as the correct size for a ROM dump of this cart ? 64K ? 256K * 2 ? 512K ? Any other size ?

It seems most of the Saturn carts have mirrored data. I only found 2 or 3 ones that don't have mirrored data, out of more than 80 carts tested. (it seems to bethe same for MPEG Carts).

 

[antime]

The mirroring is an artefact of address decoding, in this case performed by the PAL chip. Doing only partial address decoding is cheaper, but will also lead to this kind of mirroring.

Both the M27256 and 27C256 are 256 kilobit devices, which translates to 32 kilobytes each.

 

[Madroms]

Thanks antime.

I misinterpret the 256K, so now it is clear => 64K for the ROM of the Satellite.

And I will forget the mirroring stuff, ok.

 

[antime]

Forgot to add that the EPROMs are probably connected to form a single 16-bit wide memory, with one chip storing the high bytes and the other the low bytes. If you just want to dump the contents it doesn't really matter, but something you'll have to figure out if you want to do a "perfect" MAME-style dump. Charles MacDonald has been working on how to automatically deduce the fusemap of PAL devices, but it requires some custom hardware.

 

[Madroms]

Thanks again for all these additional infos.

I am more concerned by data as runable program that can be easily shared and tested than perfect ROM dump which hasn't any real purpose for the saturn.

I know there isn't any real use of dumps from ROM of saturn carts, but I think it could have some interest for devvers/debuggers/emus authors