Convert TFROM to TGROM (Add a CHR-RAM)

A place that you can discuss reproduction of classic titles or "licensed-for-reproduction" homebrew for personal use.

Moderators: B00daW, Moderators

Forum rules
1. NO BLATANT PIRACY. This includes reproducing homebrew less than 10 years old, with the exception of free software.
2. No advertising your reproductions, with the exception of free software.
3. Be nice. See RFC 1855 if you aren't sure what this means.
Post Reply
BokuNES
Posts: 42
Joined: Wed Apr 22, 2020 8:42 pm

Convert TFROM to TGROM (Add a CHR-RAM)

Post by BokuNES »

well, as the title says, thats i want to do, add a chr-ram to a tfrom (or any mmc3 board), i dont know if i need to configure the MMC3 pins to do this, there is a tutorial or someone knows how to archive this?, thanks :P
lidnariq
Posts: 11432
Joined: Sun Apr 13, 2008 11:12 am

Re: Convert TFROM to TGROM (Add a CHR-RAM)

Post by lidnariq »

The vast majority of MMC3-using games with CHR ROM don't have a metal finger on the cartridge connector for one required signal ("PPU /WR"). There's no robust way to add it, and only a very limited set of MMC3 carts that didn't start with CHR RAM have it.

Other than that process, which is a right pain, it's "just" match named signal to named signal, and most of those signals won't require any rework.
BokuNES
Posts: 42
Joined: Wed Apr 22, 2020 8:42 pm

Re: Convert TFROM to TGROM (Add a CHR-RAM)

Post by BokuNES »

lidnariq wrote: Sun Oct 02, 2022 8:02 pm The vast majority of MMC3-using games with CHR ROM don't have a metal finger on the cartridge connector for one required signal ("PPU /WR"). There's no robust way to add it, and only a very limited set of MMC3 carts that didn't start with CHR RAM have it.

Other than that process, which is a right pain, it's "just" match named signal to named signal, and most of those signals won't require any rework.
sorry, im forget to say that im only using famicom carts, witch obiously, has all his pins, considering that, its is posible then??, do you have some king of schematic to do it?
lidnariq
Posts: 11432
Joined: Sun Apr 13, 2008 11:12 am

Re: Convert TFROM to TGROM (Add a CHR-RAM)

Post by lidnariq »

HVC-TFROM only uses 64 KiB 28-pin CHR ROM, so, it's connected as here: nesdevwiki:Mask ROM pinout § 8-64kBytes (28pin) ROMs

6264 needs to be instead connected as nesdevwiki:6264 static RAM § 6264

You'll need to get PPU /WR from the cartridge connector itself - it's currently just by itself on pin 47 https://www.nesdev.org/wiki/Cartridge_connector

You'll need to rework pins 26 and 27. The rest should be fine as is. 6264 +CE should be tied high.
Post Reply