unrom 512

[acidrain97]

On the subject of unrom 512, I'm guessing there is no wiring scheme for a 27c040.

UNROM (mapper 2) 27c020 - Works for Return of the Red Falcon using only konami boards ie (rom chip is vertical)
Bend up pins 1, 2, 30, 31, 32
Solder pin 1 to pin 32, 31, hole 28
Solder pin 2 to hole 24
Solder pin 24 to GND (OE)
Solder pin 3 (32p) to pin 30

Any help is appreciated. thx

[Joe]

Nintendo's UNROM and UOROM boards are limited to 256KB. You should use 27C020 instead.

If you want to use 27C040 anyway, wiring is the same as 27C020.

[acidrain97]

I still can't get a 27c040 to work. The only difference is pin31 which is a18 on the 27c040. Is there more bank switching going on? or the board simply can't handle it. Sorry just a little confused. I really don't want to go with a "New" board unless I have to.

[tepples]

You guessed right: there are more bits going through the bank switching logic. The homebrew "UNROM 512" board has an additional bit of state corresponding to D4 (use a 74377 instead of a 74161, or add a second 74161) and an additional OR gate connecting Q4 from the '377 to A18.

[acidrain97]

What your saying is rip the 74161 out and replace it with a 74377? How would that work? 377 has 20 vs 161 has 16 pins. I would love to see someone pull that off? I don't see how you could another 161 on the board. where would you put it.

[Memblers]

The only way might be to wire it in, dead bug style. Or, building something on perfboard, then wiring that separate board in. You might not need to add all 16/20 wires, but you do need to connect unused inputs to something. In these photos here, of something not intended to fit back inside a cart shell, I shorted pins to adjacent ones whenever possible. This was stranded wire, but if you use solid core wire, you can use pliers to bend and form lengths of wire into specific shapes before soldering it.

IMG_20190907_220832_reduced.jpg

IMG_20190907_215103_reduced.jpg

[Ben Boldt]

It makes me feel very happy and nostalgic to see those chips wired up like that, being held firmly in midair by the wires. It is a work of art and I am not being sarcastic; throws me right back to good places where I belong. Thanks for sharing.

[creaothceann]

makes me feel very happy and nostalgic to see those chips wired up like that, being held firmly in midair by the wires

Reminds me of this solution.

[acidrain97]

I see your point.... I don't think that mess would fit in a cart... Answers that.

If you had a unrom that's 64k (27c512) could you drop that chip in /w no rewiring or would it be easier to use a 27c010 and rewire?

[Memblers]

Cart shells are pretty big, longer wires can work, but understandable if you want a cleaner way.

IIRC, 27C512 does need rewiring for UNROM. But at least it's 28 pins like UNROM PRG socket, 27C010 is 32 pins and might not fit around the other parts.

[acidrain97]

I tend to use konami boards (rom chip is vertical). Easy to work with but those pads are sensitive to solder suckers. Solder braid works better.

Thanx