This is an archive of a topic from NESdev BBS, taken in mid-October 2019 before a server upgrade.
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by on (#75024)
so if a NROM has CHR RAM, anybody know how to put it on a cart? i tried just putting a WRAM chip on the CHR and it didn't work. is it like when making FF3, does it need to be rewired? i just did a straight solder.

by on (#75026)
Yeah exactly you'd just need to add the /WE pin so that it works as expected.
By the way it should be easier to use an UNROM devcart or something in the like if you already have one.

by on (#75029)
Bregalad's solution would work fine for a 16 KiB ROM (NROM-128), as long as it's properly doubled to fill the ROM. For a 32 KiB ROM (NROM-256), the PRG ROM bank loaded into $8000-$BFFF at power-on is undefined. To use it on an UNROM cart, you'll need to add a stub to the reset handler somewhere in $C000-$FFFF that maps the first bank into $8000-$BFFF:
  ldx #0
  stx reset+1
  jmp real_reset

Then your vectors would be nmi, reset_stub, and irq.

by on (#75036)
This isn't even necessarly, what I meant is that if you have a 32kb EPROM and a UNROM devcart, puting the 32kb EPROM on the UNROM devcart has a 6/7 probability to work. It won't work if you are unlucky enough so that bank 7 is swapped at $8000-$bfff at power up.

by on (#75051)
Hey, maybe you could use that to seed your PRNG :D Put seven different seed values as the first byte of your low seven banks, then on power up lda $8000 and use that as your seed.

Seriously though, you should just be able to solder a wire from the Write Enable pin on the edge connector to the Write Enable pin on the RAM chip.

by on (#75088)
This won't work as I think a 74HC161 will reset in the same state. However different 74HC161's will reset in different states.

Note that this is completely untested. Maybe they all always reset to $0 or to $f, I have no way to know currently I should do more testing.

by on (#75090)
ill try it out with the an unrom board this weekend and let you know how it goes