NAOMI Dual Bios on a single EEPROM solved

OldFoo · Post by **OldFoo** » Wed Dec 17, 2008 5:56 pm

Looks like NAOMI Dual Bios on a single EEPROM solved

http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 0327258126

N' E' One seen this.

I would like to get the images

OldFoo · Post by **OldFoo** » Sat Dec 20, 2008 12:26 am

Bump.

This is cool. Anyone have any info.

I am probably going to buy two.

Which combo would be best?

These are for NAOMI 2 (I might get one for my NAOMI 1)

JPN/EXP (would be my guess)

Does JPN/USA offer any benifits?

Should I maybe get one of each.

Input Welcome

Thanks

Bob Presutti

OldFoo · Post by **OldFoo** » Sun Dec 21, 2008 12:45 am

Looks like its just bank switching to me..

OldFoo · Post by **OldFoo** » Sun Dec 21, 2008 6:23 am

It's simple.

If the board takes a 16Mb EPROM then program the lower half of a 32Mb EPROM with one BIOS and the upper half with the second BIOS.

Set up a single pole, double throw (SPDT) switch. Left pin to ground. Right pin to +5v. Center pin goes to the highest address pin on the 32Mb EPROM.

Switch that address pin to ground to access the first BIOS. Flip the switch the other way to tie it high and access the second BIOS.

A quick look at the data sheets tells you all you need to know about which pins to wire up to that switch.

If the pin you need to switch is grounded or tied high on the NAOMI then you'll need to either bend that pin out or clip it short so it doesn't fit in the socket.

Oh, and never flip the switch with the power on. The game will go berzerk.

RJ

OldFoo · Post by **OldFoo** » Sun Dec 21, 2008 1:48 pm

I looked into this quite some time ago, and vaguely remember some snag concerning byte/word mode when using an eprom that was twice the size of the naomi bios - and that a possible solution would be to interleave the images in, never bothered to try it.

Have you guys actually done this?

OldFoo · Post by **OldFoo** » Sun Dec 21, 2008 2:00 pm

I Haven't, I was told it didnt work with switching the banks so never tried it..

OldFoo · Post by **OldFoo** » Sun Dec 21, 2008 5:54 pm

I remember looking into this a while back and found that the 32Mb direct equivalent of the Naomi bios had a slightly different pin configuration. If someone got this to work, I'm curious how they did it. :smt017

OldFoo · Post by **OldFoo** » Sun Dec 21, 2008 10:03 pm

joshua3dg wrote:I remember looking into this a while back and found that the 32Mb direct equivalent of the Naomi bios had a slightly different pin configuration. If someone got this to work, I'm curious how they did it. :smt017

Me Too. I know there have been several threads here about this but it looks like someone figured it out.

Bob Presutti

OldFoo · Post by **OldFoo** » Sat Jan 03, 2009 11:16 am

Any outcome on this, did anybody get one ?

OldFoo · Post by **OldFoo** » Sat Jan 03, 2009 11:47 am

The seller of this Naomi Dual Bios is hoellentaucher77, he is also member in this forum. He told me, that the Duals Bios Epproms he gets (from another seller or shop?) are faulty and that he will never sell one of them anymore.