nesdev.org

This is an idea that came to my mind while working and it's all hypothetical. I'm no hardware expert so keep that in mind while reading this post

Let say for example that I had a MMC3 CHR-RAM cart. For some strange reason, I decide to add some extra controller (74X???) to this cart that would react when writing to a specific address range. When I would write to it, it would switch the address line of the CHR-RAM to the CHR-ROM.

First, would that be even possible? Maybe the chip mentioned is wrong but I least the concept is to switch the chip at run-time. This would allow to use CHR-RAM when you requires specific video effect and CHR-ROM when some level doesn't requires it.

I don't know if it would be that useful but now that the hardware is cheaper, the possibility to switch between both chips seems interesting but I'm not sure yet how it could be used.

Maybe my idea is crazy but like I said, I'm no hardware expert so..

pinbot and high speed have MMC3 boards that use both CHR-RAM and CHR-ROM.

e: the NES-TQROM board

Oh... Didn't know about this one. So it does exist. Thanks for pointing this out!

Sorry for my ignorance

Edit: Now if the wiki could be working.. I could check the info about this board. Hope is just a temporary downtime.

wierd, I figure it'd be hosted on the same server as this forum. I checked kevtris's site but it only describes the features of TQROM without any register details from what I saw. disch's mapper docs would help, they're on RHDN I think.

ok. I will give it a look once the wiki is up or check Disch's mapper doc that I have somewhere.

I did a quick check to see how many games support this setup by looking at Bootgod's database and there is only 2 and maybe no (?) japanese ones too so that board is very rare. And for some reason they only have 64k of chr-rom so I want to figure out later if this is a limitation of that setup or just they only used 64k for some reason since MMC3 can support up to 256k of chr-rom.

Regarding the wiki, no, it's not hosted at the same place. We had some argument regarding this subject recently.

Pin Bot and High Speed use an upper CHR address line from the MMC3 as the ROM/RAM select, so the board should do 128KB of each after rewriring. As is the board only does 64KB because it uses the 28 pin ROM. RAM can be banked just like the ROM. I would guess the games use it for animated tiles, but it isn't a common board so there should be a pretty good reason to use it if you plan on real hardware.

The N106 allows for both CHR ROM and CHR RAM. One can select 4k CHR banks, and 2 of those 4k pages are CHR RAM. Though I recently read that this mapper is nearly impossible to make a dev cartridge out of, because all of the chips are glob-tops.

I'm guessing that if you have a spare enable line on a RAM and a ROM, you can transform any T*ROM board with an intact PPU /WE into a TQROM compatible board: use a 74HC04 inverter to decode CHR enable.

Celius wrote:The N106 allows for both CHR ROM and CHR RAM. One can select 4k CHR banks, and 2 of those 4k pages are CHR RAM. Though I recently read that this mapper is nearly impossible to make a dev cartridge out of, because all of the chips are glob-tops.

Didn't know about this one too. Regarding the dev cartrige, Sdm made one here. The game he used was Dragon Ninja (Bad Dudes). I was able to find a cart that doesn't have glob-tops but didn't have time to make a dev-cart myself. And this one seems to support the music chip since he made a Megami Tensei II game with it (you were looking for that in another post if my memory is good).

tepples wrote:I'm guessing that if you have a spare enable line on a RAM and a ROM, you can transform any T*ROM board with an intact PPU /WE into a TQROM compatible board: use a 74HC04 inverter to decode CHR enable.

Good to know. I may try someday to convert a FF3J to this format but for now this is an extremely low priority. Now that I know games were already made that way then I don't have the same interest as if it was never done before. It would a nice experiment thought.