Changing UNROM to UOROM

Discuss technical or other issues relating to programming the Nintendo Entertainment System, Famicom, or compatible systems.

Moderator: Moderators

Post Reply
Pennywise
Posts: 70
Joined: Tue Jul 14, 2009 11:04 am

Changing UNROM to UOROM

Post by Pennywise » Mon Dec 20, 2010 4:18 pm

Both of these boards seem to be the same aside from the PRG size limits. So let's say that I expand the PRG-ROM of a UNROM to 256K, would it automatically become UOROM? They're both listed as the same mapper, but if I swapped in a 16K bank from the expanded space, would the NES/emulator recognize it? Thanks

User avatar
hap
Posts: 355
Joined: Thu Mar 24, 2005 3:17 pm
Contact:

Post by hap » Mon Dec 20, 2010 4:44 pm

Both of these boards seem to be the same aside from the PRG size limits. So let's say that I expand the PRG-ROM of a UNROM to 256K, would it automatically become UOROM?
the physical board: no
the iNES ROM for emulators: yes

the other question: yes

User avatar
Dwedit
Posts: 4408
Joined: Fri Nov 19, 2004 7:35 pm
Contact:

Post by Dwedit » Mon Dec 20, 2010 5:10 pm

Some emulators even let you use 4096K size roms with Mapper #2 selected.
Here come the fortune cookies! Here come the fortune cookies! They're wearing paper hats!

User avatar
tokumaru
Posts: 11991
Joined: Sat Feb 12, 2005 9:43 pm
Location: Rio de Janeiro - Brazil

Post by tokumaru » Mon Dec 20, 2010 7:00 pm

One important detail to keep in mind is that UxROM has bus conflicts, so mapper writes must be made to ROM locations that contain the same value as the one being written. Because of this, games usually have a table with the values necessary to select all the possible banks.

With UNROM, there are 8 possible banks, but UOROM allows for twice that, so if the bankswitching table doesn't increase to accommodate the new page indexes, there will be problems when trying to select pages from the upper half of the ROM.

User avatar
MetalSlime
Posts: 186
Joined: Tue Aug 19, 2008 11:01 pm
Location: Japan

Post by MetalSlime » Mon Dec 20, 2010 8:33 pm

Also, make sure that your fixed bank remains the very last one. If you insert extra space into an UNROM rom to make it UOROM, it should come before the fixed bank.
MetalSlime runs away.

User avatar
Bregalad
Posts: 8008
Joined: Fri Nov 12, 2004 2:49 pm
Location: Chexbres, VD, Switzerland

Post by Bregalad » Wed Dec 22, 2010 4:17 am

I guess people are confusing things.

UNROM and UOROM are just names printed on Nintendo's boards - mapper 2 is an abstract concept that has a larger scope than Nintendo's board implementing them.
Mapper 2 can be used by 3rd party games, or even ROMs who were never put on a real cart etc.... it's not restricted to UNROM boards.

On the other hand, "Crazy Clibmber" uses an UNROM board and is not mapper 2.
Useless, lumbering half-wits don't scare us.

tepples
Posts: 22278
Joined: Sun Sep 19, 2004 11:12 pm
Location: NE Indiana, USA (NTSC)
Contact:

Post by tepples » Wed Dec 22, 2010 8:43 am

Thank you for pointing out that the board in Crazy Climber is in fact UNROM. After checking on NesCartDB, I went and tried to clarify this on the wiki: UNROM is most commonly mapper 2 but occasionally mapper 180.

User avatar
tokumaru
Posts: 11991
Joined: Sat Feb 12, 2005 9:43 pm
Location: Rio de Janeiro - Brazil

Post by tokumaru » Wed Dec 22, 2010 2:51 pm

What's so special about 180?

User avatar
Bregalad
Posts: 8008
Joined: Fri Nov 12, 2004 2:49 pm
Location: Chexbres, VD, Switzerland

Post by Bregalad » Wed Dec 22, 2010 2:57 pm

It's exactly like mapper 2 exept that it's the low bank which is hardwired and the high bank which is switched. It is also made with an UNROM board, by replacing the 74HC32 quad-or gates with a 74HC08 quad-nand gates.

Just to say that UNROM is a board, mapper 2 (and 180) are concepts. There seem to be confusion arround this, because it has been said too many times that "mapper 2 is UNROM" which isn't exactly true.
Useless, lumbering half-wits don't scare us.

User avatar
Memblers
Site Admin
Posts: 3897
Joined: Mon Sep 20, 2004 6:04 am
Location: Indianapolis
Contact:

Post by Memblers » Wed Dec 22, 2010 6:09 pm

The boards do say LS32 on it though, so that shows how it was "supposed" to work. Crazy Climber is the only different one (Famicom only).

User avatar
Bregalad
Posts: 8008
Joined: Fri Nov 12, 2004 2:49 pm
Location: Chexbres, VD, Switzerland

Post by Bregalad » Thu Dec 23, 2010 4:58 am

True, but even if Crazy Climber didn't exist you still couldn't just say "mapper 2 is UNROM" because anyone can implement somehting functionally identical to mapper 2 with more/less bits, with/without SRAM or bus conflicts, and with non-UNROM boards.

The same remains true for all discrete logic mappers... the mapper is a concept behind the discrete logic, not the board Nintendo put this logic on. (as opposed to ASIC mappers, you could say for example that "mapper 1 is MMC1", but you couldn't say "mapper 1 is SNROM").
Useless, lumbering half-wits don't scare us.

Post Reply