It is currently Wed Apr 24, 2019 11:03 pm

All times are UTC - 7 hours

Post new topic Reply to topic  [ 1 post ] 
Author Message
PostPosted: Wed Sep 18, 2013 7:52 pm 

Joined: Sun Sep 19, 2004 11:12 pm
Posts: 21324
Location: NE Indiana, USA (NTSC)
In this post, infiniteneslives wrote:
With [extra PRG-RAM] being a motive for people to make the leap to MMC5 it seems like a worthwhile addition. If we were to take it one step further it might be useful to have one of those bits designate a means to put PRG-RAM in $8000-FFFF. Possibly use bit 4 to swap out the last PRG-RAM bank with the ROM bank that is otherwise fixed to the 2nd to last bank? [...] Might be a good idea to use bit 5 to designate the bank in ROM as read only or r/w. ALL of this is back-compatible.

That'd need a new mapper number because existing mapper 4 ROMs may already be writing 1 to bits 4 and/or 5. Just having bits 3-0 control the bank number would be fully backward compatible with the existing 8K definition and wouldn't need a new mapper or NES 2.0 submapper, as those address outputs are just not connected to the RAM on the existing board.

That and I'd like someone with a logic analyzer to see if FME-7 still outputs the bank bits when RAM is enabled in $6000-$7FFF.

To make it clearer what I'm talking about, here's the behavior of mapper 69 (FME-7, Sunsoft 5B):
7654 3210  Register 8: PRG RAM control
|| | ||||
|| +-++++- Select 8 KiB bank of PRG ROM at $6000-$7FFF
++-------- Chip select: 0: ROM; 1: Open bus; 3: RAM

I'd like to know who can test that B works even when RAM is selected.

And a proposed homebrew extension to mapper 4 (MMC3):
7654 3210  $A001: PRG RAM control
||   ||||
||   ++++- Select 8 KiB PRG RAM bank at $6000-$7FFF
|+-------- 0: Allow writes to RAM; 1: Read-only
+--------- 0; Disable RAM; 1: Enable RAM

Pin Eight | Twitter | GitHub | Patreon

Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 1 post ] 

All times are UTC - 7 hours

Who is online

Users browsing this forum: lazigamer and 2 guests

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Group