I've been doing eletrical modding for a few years now, but I never got deep into microchips and the such. So im kind of a newb, I feel so stupid
Ah well, heres the quesiton.
I trying to hardwire in a game to my NES (TMNT 2 mmc3b because it had a crack in the case, so its a tester) and be able to switch between it and the one in the cart bay. I figured it would be as simple as wiring it to the pins and switching them opened and closed, but so far its been a bit more complicated. My oringal idea was to use switching transistors wired along with DPDT switch (DPDT because I have a bicoloured LED indicator). Heres the schematics for it
http://i57.photobucket.com/albums/g224/ ... ircuit.jpg
I just link to it since its a bigger picture. (sorry for the sloppyness. I dont have a circuit designing program or anything so i just used the gimp)
I was told however this will not work. Since some pins on the carts do not have just one polarity. electricy travels back and forth on some of them which would fry the transistors.
Now I was talking to someone who did a built in Super mario bros arcade game NES and he was telling me I could simply disable the ROM's on the cart by running high (+5v i understand) to pin 50 and pin 58 (I think 50 is /CE and 58 is a13 although I have no idea what that means
) He also mentions something about the PPU being bipassed throught the cartridge so it could disable the PPU or change the mirrong from vertical to horizontal on the fly for the game through pin a10 (again no idea what that means
). I understand how that could hinder the game in the cart bay useless if its getting wrong signals from the hardwire, but im not sure exactly whats going on with mirroring.
So heres pretty much what I gather from it. I have to be able to send a high signal (5v) through pin 50 and 58 to the cart and disable pin a10 going through it so the ppu cant access it. I could controll this with a DT3P switch (well DP4P, one for the LED indicator.)
Does this make much sence? Sorry for asking newb questions but I'm afraid I just don't know and would like the answeres. Thanks in advance
p.s you can see the work in progress log on xbox-scene forums (Thats what I usually mod, but im trying to get into retro) here:
http://forums.xbox-scene.com/index.php?showtopic=510055
lungdart wrote:
I've been doing eletrical modding for a few years now, but I never got deep into microchips and the such. So im kind of a newb, I feel so stupid
Ah well, heres the quesiton.
I trying to hardwire in a game to my NES (TMNT 2 mmc3b because it had a crack in the case, so its a tester) and be able to switch between it and the one in the cart bay. I figured it would be as simple as wiring it to the pins and switching them opened and closed, but so far its been a bit more complicated. My oringal idea was to use switching transistors wired along with DPDT switch (DPDT because I have a bicoloured LED indicator).
It's even simpler. Just hook the cart up, but control /CE to the PRG ROM and CHR ROM on it. and if it's got WRAM, /CE on that too. Let it pass through (for the "built in" game) or force it high (for the cartridge game).
Simple as a 3 pole switch and 3 resistors. each signal passes through the switch when it's in 1 position, and then the resistors pull the signals up to 5V when it's in the other position.
Or as many famiclones do, wire the internal pcb and cartridge slot up in a way where you don't use all the extra ground lines, then use that extra line to controll a 4066 to automatically turn the internal cartridge off when one is plugged in.
Thanks for the replys guys! I doubt I could figure out how to get a 4066 to controll disabling the carts, I'm not that experienced. But just setting a few pins high is dooable in my eyes! Ill just have to fire up a schematic on how to get it bumping with the DPDT switch I already have wired with my bi coloured LED. Can't wait for that funkyflashcart and be able to have a nice USB port in the back of the NES that I could flash the flashcart built in. That will kick ass!
edit: Came up with an idea for being able to use my current DPDT switch in the NES (Since its in line with a second one it would be hard to find the same style in a Dt4p switch) Anywho here it goes.
the switch will provide power to two switching NPN transistors. One for each chip (chr/prg). When the power is fead through the base of the transistors the collector sends a 5v signal down the emitter to a OR gate into the /CE's of the chip. On the other pin of the OR gate will be connected regularly. So when the switch it hit, the led changes and the transistors pull 5v into the or gate to the /CE which will make it constantly 5v. when the switch is off the 5v wont go through and the /CE will be connected through the OR gate to the cart pins. This way the /CE can communicate normally and I can force it high as well witha DPDT switch, what do you guys think?
Why are you even using transistors? TTL can easily sink/source acceptable LED current. Something like this would do:
oops. it's nInt/Ext in the diagram
If you want a bicolored LED, activate one with the select input, the other with the inverted select input.
I'll use transistors because Its what I understand. It may be wrong in your eyes but if it works, it works and thats good enough for me! Otherwise I will try to wrap my brain around your diagram. The OR gate I think I'm going to use is a cmos 4071. ITs a simple quad 2 input OR gate.
You'll need more than 4 OR gates though since CHR has both RD and WR control signals, also /A13 prolly selects the CHR ROM. To be safe, I'd gate all the control signals from the external cart, and whatever few the internal game uses.
If you use CMOS like a 4071, make sure you use something TTL compatible, or just use a 7432 which I think even has the same pinout. Sorry I should have made it prettier/cleaner. nInt (internal) / Ext(ernal) is a select line, it allows the active low signals to pass on one cart, and it gates the others. When you flip the switch, the other cart will become active and the first will be held inactive because of the inverter.
PS: I wouldn't get my hopes up about Funky flash, I don't think artohs around anymore, we haven't been upgraded on any progress in many months
Again im kind of newbish here and I do not know what TTL is, other then its some standard. ITs kind of over my head at the moment, but I reallly apreciate all this feedback. I already ordered 5 4071 cmos chips off ebay for $2 or something, also a 72 pin card edge connector to replace the one in the NES but thats a different story.
As for using the transistors, that is a stupid Idea. I can just run the 5v in series through the entire circuit and cut it off before it branches off to each or gate (leaving one straight through to power the chip) Im trying to wrap my mind around this nInt/Ext pin. Was the NES designed to have built in games? other what is this really for?
So I coudltn just set the /CE signals on each chip high to disable the ROMs? That was the kind of solution im going for. It seems there your rerouting the /RD and /WR to the roms so they can/can't go to the NES at the flick of a switch. That seems to over complicate things. Couldnt just setting /CE on the chips high disable them so they wont even send /RD /WR signals? I could blindlessy wire your diagram below and hope it works, but I'm the kind of guy who wont do anything unless I understand it. I'm here to learn first, to mod second!
Also what program did you use to create the schematic? Is there something easy or is everyone using paint/photoshop/gimp. I hate using those, It would be great if there was a program out there for that, prefferably for Linux as thats what I use.
TTL is a logic family, it's older than CMOS and is what the NES uses, pretty much anything that runs off 5V uses TTL somewhere, even if for menial jobs where CMOS is used in high speed parts. In a nutshell, TTL can be thought as 0V = 0, 5V = 1. CMOS is more flexible and may not strictly output the desired TTL voltage for a logical 1 or 0. Many older CMOS chips are directly compatible with TTL so they can interface with TTL like the NES, I think you'll be fine with your CD series chips. I would have gone with 74LS32s however because they're far cheaper and without a doubt compatible.
OR gates can be used to allow signals to pass by feeding one of the gates' inputs a low. OR gates will only output a low when both inputs are low. In my design I simply gated the control signals going to both the internal game and external cartridge by putting a 1 on the OR gates. This would make ALL of the OR gates output high which would keep both carts inactive. By putting an inverter in there and routing the inverted input to half the gates (in my case the external cartridge), half of the OR gates will be always high, half will be whatever the NES control signals are. When you flip the switch, the other half will be active/inactive.
I don't know what you mean by running 5V in series through the circuit or branching off to OR gates. Can you please draw a diagram? You do not want to use OR gates to power more OR gates if that's what you're thinking.
NES wasn't designed for built in games, the control signals are so that the cartridge knows when to output data without conflicting with another process and so that it can find out what the console is doing.
When the NES asserts /A13 (with 0V, it's active low), that usually enables the CHR chip select. When the NES asserts /RD while the CHR is active that tells the CHR it's okay to output data on the data bus. The /WR signal is used when the game has CHR-RAM instead of ROM or extra VRAM.
Yes, setting the PRG /CE signal high will disable the PRG ROM, but it will not stop the system from writing to SRAM or other things the cartridge maps into NES memory. If you don't disable everything, games can conflict with eachother if the carts have similar features.
Using OR gates means you don't have to use a huge switch with pull up resistors. I don't think my design is overcomplicated at all, I can't think of an easier way with OR gates. Please note my design would need to be expanded for /A13, you may even be able to remove CHR /RD and /WR
depending on the built in game.
Definately do not blindly wire up my diagram, you must understand it to build it correctly since I only included a few control signals.
To make the schematic I used a Windows program called Logic Works, a digital circuit simulation tool. It's strictly for digital systems, but you may find it helpful for understanding things like my diagram since you can quickly simulate designs in real time with high level symbolic components like binary decoded displays and binary switches without the implied pins like VCC.. Maybe it works in Wine, you should check it out. I prefer it for digital stuff to Multisim or other more "professional" (what a joke) simulation apps.
Lol again that was stupid of me. I completely understand your diagram. My mind was just over complicating things. This is definatly way better then what I was thinking. I don't suppoese there is anyway to make a NOT gate out of OR gates is there? I seriously doubt it.
I did see that the cmos chip could take anyway from ~3 to ~15 volts for input, but I just assumed if I put in 5v, it would be fine. Hopefully theres no conflicts there, Its nice to know the difference now though. Again this is a big learning experience for me, and you guys have been really great and forgiving of my stupidy so far
Ill try to make more sence of what I was trying to do with the wiring withought drawing a pciture, photobucket is a hassel, and this isnt that important anymore, lol. I wanted to put a switch on a 5volt line, and then run all the OR gates on one input off that line AFTER the switch. So one switch could turn off (set low) multiple OR gates.
As for expanding for /A13 do you mean just adding an OR gate for that as well? Or do you mean somethign more. thanks for all your help!
lungdart wrote:
As for expanding for /A13 do you mean just adding an OR gate for that as well?
Yeah, but you should check what the internal game uses to enable the CHR, if it only uses /A13 for both /CE and /OE, there's no reason to gate additional signals internally. You should still gate other stuff on the external cart though.
You cant make an inverter/NOT gate with OR gates, but you can with a NOR, just wire the two inputs together. It would have been possible to implement the thing in two 7432s and a 7402, for like US$0.50
I don't think I will need the inverter since The switch thats in the NES now is a double throw. I could have two different 5 volts, one for each set of OR gates. one position 5 volts will go to the internals, meaning that the cartridge will work, one position the 5 volts will go to the cartridge connecter meaning the internal game will work. I bought 5 of these quad OR gates so I have a total of 20 two inpurt OR's to work with. Ill just put them infront of everything that could potentially cause a problem. Rather then going through the complicated process of trying to figure out how the game enables the CHR. (put one for /CE, /A13, /RD /WR etc) I'll let you know how it turns out when I get the gates, thanks!
I am thinking of doing the same project with a Famicom clone I have here. So basically I need to gate the CE's and A13?
Does anyone know the pinout for CHR & PRG to a 60 Pin connector?
www.benheck.com/Downloads/NES_Famicom_Pinouts.pdf
This has both pinouts layed side by side for comparison. Enjoy!
wired it all up only to find that the cpu was fried. Guess that would've been obvious considering the 5v regulator had blown.
Was it blown before or after wiring it up?
9V AC going into the NES mobo would def fry things to a crisp.