help programming my NES cart

help programming my NES cart
by on (#7089)
hello, so im still pretty new to all this, and im kinda just fumbling as i go along. i have built a working nes ROM, and as i understand it, i can now burn it to a cart. assuming i have all the necessary equipment, ive taken the ROM, chopped off the first 16 bytes (NES header, right?) and then the last 8k, which is my CHR.

Now, the PRG bin im left with is only 16k, and my CHR, as I said, is 8k. Im not exactly sure how to proceed from here. Ive been told i need to copy the CHR four times, to get it to 32k and burn that to a chip--is that true?

I guess one of the real questions if what donor cart i should use. In the nes mapper doc, i saw 'Tennis' is 16k PRG / 8k CHR and mapper 0 (which I use), would that be a suitable donor? do i always have to match up the PRG/CHR and mapper? and if so, would i just burn the 16k PRG BIN and the 8k CHR bin straight to chips (as opposed to quadrupling the CHR, or something like that)?

thanks heaps, i really appreciate any help

by on (#7090)
Buy a 8k eprom and a 32k eprom, burn the CHR and PRG (mirror two times) on them, respectively. Solder 2 28-pin sockets to a NROM-256 (32k prg) cart and insert the eproms on them. I'm not sure how to do it for a NROM-128 (16k prg) cart tho.

by on (#7092)
Having a 16k EPROM for PRG and not mirror anything should work just fine. Yeah, using no mapper is a NROM card, I don't know if there is much difference between NROM-256 and NROM-128. I think NROM-256 has just one more line to the PRG bus.

by on (#7106)
hmm, so to be totally clear:

any unrom-256 cart will work? super mario bros, etc?

assuming i already have 32k EPROMs, i burn my 16k PRG—repeated twice and my 8k CHR—repeated four times?

sounds like the point is you dont want any empty parts of the chip, and that the chr/prg should fill up all 32k of the chip. is that correct?

by on (#7107)
Yep, Super Mario Bros. uses that board, the single version anyways, not the SMB/Duck Hunt combo. And that is correct on the ROM sizing. Depending on what your intending on playing, you may need to switch the mirroring select pads on the board, or if you plan on changing ROMs often, putting a switch there would be even better.

Just to be clear, it's NROM-256, not UNROM (there is a difference).