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 Post subject: Which pins to where?
PostPosted: Sun May 21, 2006 4:54 pm 
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Ok. I have attempted two MMC3 dev boards so far both to no avail.

The first one I bent pins up and soldered them according to THIS site, but it didn't work.

The second one just got me plain confused and I stopperd before I made a permanent mistake.

Here is the board I have ready for chips and wiring. I have cut the circled tracks.

The problem is that the three places I have for wiring all are conflicting. Can someone please help me out with what to solder where (even re-posting the scans with colored lines would help. The sites I have referenced are ROM LAB and the NESDEV ... but both areas conflict.

Thanks a lot, gang.

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PostPosted: Sun May 21, 2006 7:56 pm 
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I also failed in my first experiment with MMC3, and that kinda traumatized me.

I think the problem is with the "special" pins. Some of us, that know squat about electronics, heavily rely on guessing where /OE, /CE, /WE, Vpp and such pins that are more complicated go. With the numbered A's and D's there is no mistake... but some PRG pinouts of NES mask ROMs have no /OE, for exemple... CHR has something special going on with /OE... What about Vpp or /WE? Should these go to GND or to +5V?

I don't know... I'm tired of wasting money on programmers, chips, carts... and not seeing the results I expected. I'm kinda holding off until I try that rewiring stuff again... I don't wanna loose any more carts.

Every day someone says something new about rewiring. Maybe if we wait a while, we'll gather enough info? Like... it took a while until someone mentioned pins shouldn't be left floating... and that seems like precious info!

Ah... whatever man... I'm almost paying someone to teach me that stuff or even do that for me. But you know, I'm stubborn, I'm sure I'm gonna try something soon anyway, and get frustraded, of course.

Yeah, sorry if that was innapropriate, but it seems like a lot of us are having trouble with that lately.

EDIT: Sorry... noriaki_kakyouin, it would be better if you mentioned the chips you are using... regular EPROMs (27Cxxx)?


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PostPosted: Sun May 21, 2006 8:32 pm 
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It's ok. I'm just glad that others are having difficulties with MMC3 as well... those diagrams just make no sense.

I am using 27c020/27c010 chips. Not flash, but I really didn't need flash since i'm trying to make my carts single game carts.

I decided tonight, however, that I should REALLY make a DEV cart so that I can make sure the chips I program are functional... but the problem comes back to the wiring diagrams.

I looked in my EARTHBOUND cart that NES Reproductions made for me, and once again the wiring was weird in that he connected pin 1 to pin 32 on both the PRG and 1 to 32 on the CHR. I think that answers the "do not leave floating pins" bit you were talking about.

The diagrams on the ROM LAB page were informative for the PRG connections, but the CHR had no image of pins connected and, since the CHR is very complicated, it really lost me. I hope someone can help us.


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 Post subject: Devcarts
PostPosted: Mon May 22, 2006 6:22 am 
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You guys are really taking it too hard. The NES cartridges are really very forgiving. I've done all sorts of weird stuff to mine, like cracking resistors, ripping off solder pads and traces and sticking wires all over the place. I've even cut off the mapper chip from a CNROM and stuck it on a NROM. The timing is slow enough that you can get away with almost anything. Most of the pins are the same on the mask (original) ROM and EPROM. I started out with a mapper 0 (NESROM or NROM) which is much easier as hardly any pins need to be changed. You might try one first if you have limited electronics experience.
I have made devcarts for NROM, CNROM, SLROM, SKROM, SNROM, TLROM, TSROM, TKROM, AOROM, ANROM, AMROM and Quattro Camerica cartridges and they all work reliably. I have used the wiring diagrams on the web and they are generally correct with occasional minor errors on some sites. You have to be really compulsive about planning what do do about pins that are different from mask<->EPROM. Find out where all the traces go and figure out where you have to connect the pins to. You must make sure that the pins are properly soldered and connect to the proper places on the mapper chips and the NES connector. I check each EPROM pin and make sure it goes to the right place with a multimeter. Also make sure the connections are well soldered and you haven't forgotten to solder some pins. The unsoldered pins will be intermittent and very annoying. This project will be really hard if you have not done years of playing around with soldering onto PCB's or breadboards and electronics but it is not magic and it can be done. If you are really stuck, I will try to find the time to take a cart apart and take pictures of the modifications.


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PostPosted: Mon May 22, 2006 8:17 am 
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I know I have no problems with the actual physical modification of the carts. I can desolder the MASK ROMs and solder sockets in just fine. I made 2 NROM devcarts and one UNROM (wich required rewiring of just one pin, so that was easy). My big problem is figuring out where the more special pins go. And PRG seems easier to handle than CHR.

I guess I'll use the cart pinout and find out what each hole is, instead of using the documented pinouts of the MASK ROMs to figure out the rewiring.


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 Post subject:
PostPosted: Mon May 22, 2006 8:25 am 
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It would be nice if someone who has made a few devcarts from different *rom's made a few tutorials or just put all the information together with some screenshots of there work.

It would really help a lot of us out who are having a hard time finding the information and figuring out which is correct or not.


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 Post subject: Re: Devcarts
PostPosted: Mon May 22, 2006 8:27 am 
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Lloyd Gordon wrote:
If you are really stuck, I will try to find the time to take a cart apart and take pictures of the modifications.
We're really stuck. (laughs). Pictures would be fine, but even just a simple definitive pin wiring scheme like shown at ROM Labs.

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 Post subject:
PostPosted: Mon May 22, 2006 9:09 am 
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Quote:

I think the problem is with the "special" pins. Some of us, that know squat about electronics, heavily rely on guessing where /OE, /CE, /WE, Vpp and such pins that are more complicated go. With the numbered A's and D's there is no mistake... but some PRG pinouts of NES mask ROMs have no /OE, for exemple... CHR has something special going on with /OE... What about Vpp or /WE? Should these go to GND or to +5V?

Easy.
If there is no /OE, (inverted output enable), you'll want the output to be ALWAYS enable, so since the signal is inverted always have the logical value '0', so tie it to GND.
Vpp (and also P, wich is present on some eproms) is here for programming voltage (+12V) and is unused once the chip is programmed. It can be either VCC or GND, but AVOID LET IT FLOAT !
Look at your retailer's datasheets to know more. I normally solver it to pin 32 (or 28) that is the closest VCC available.
/WE is only here on RAM chips. I think it also is here on EEPROMs. On RAM chips, you have to tie it to the right place. On EEPROMS, you will want to disable write to it, so /WE wil always have the locial value '1', beacause it is inverted. So tie it to VCC.

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 Post subject:
PostPosted: Mon May 22, 2006 9:38 am 
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Thanks Bregalad. I'll hold off a little until I feel more confident, though.

Bregalad wrote:
/WE is only here on RAM chips. I think it also is here on EEPROMs. On RAM chips, you have to tie it to the right place. On EEPROMS, you will want to disable write to it, so /WE wil always have the locial value '1', beacause it is inverted. So tie it to VCC.

The Flash ROMs I use have it. With my NROM devcarts, /WE was fine when connected to +5V, so I guess you are right.


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 Post subject:
PostPosted: Mon May 22, 2006 10:17 am 
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And if there is other pins you're not sure about, refer to datasheets and try to understand how your chip works.

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