Breakout board for N64 Expansion Port.

Discussion in 'Nintendo Game Development' started by Cybertronic, May 24, 2019.

  1. Cybertronic

    Cybertronic Member

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    I have been racking my brain on how to build a connector that fits under the N64 for development purposes.

    Long story short, I need to be able Connect a Cartridge to the underside of the N64 in order to make use of Expansion Cartridges like the Modem Cartridge or Video Capture Cartridge WITHOUT the 64DD. ie: 64Drive/EverDrive + Modem Cartridge connected at the same time allowing for 64DD cart conversions to use the accessories.

    Is that expansion port 100% custom or does something out in the wild happen to fit it? I have looked at 50 pin SCSI cables, I have even looked at the 50 pin telco connectors on phone punch blocks.

    At this point I wonder if I am better off just developing a Daughter board with two cartridge ports that sits on the top or a ordering a custom PCB that is the right thickness for the EXT port at the bottom. The ports share the same lines, just mirrored and take turns communicating so It may not be such a bad idea to go that route.

    Originally I wanted to make a CF Card Based hardware re-implementation ($$$) of the 64DD that Connects under the N64 and could use the Accessory Cartridges, but then I thought, why not just have a 64Drive or EverDrive talk to them instead? So I could theoretically boot a cartridge from the bottom connector, but that will require custom hardware, or I could put two cartridges up top, which also requires custom hardware, but easier to source parts.

    Your feedback is greatly appreciated.
     
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  2. josiahgould

    josiahgould Spirited Member

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    Spitballing here... Could you somehow use a GameShark as a passthrough and access the cartridge attached to the back?
     
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  3. abveost

    abveost Robust Member

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    Whatever you do will require "custom hardware". If you only need one borrow the adapter inside a v64.
     
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  4. Cybertronic

    Cybertronic Member

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    That would require streaming the 64DD disk rom through the Parallel port on the back of the game-shark while the cart is attached to the top, but that could technically work given the right software, barring any bandwidth or I/O limitations

    Its difficult to track down the adapter that fits between the V64 and the Expansion port. They are almost as rare as the unit itself and I cannot mass reproduce those.

    I am aware either solution will require custom hardware as stated in the original post, but it seems easier to get something that fits in the top cartridge slot, so I will probably just go that route. I can get cartridge connectors all day. That way it would be possible to connect say the 64DD modem cart and boot a 64DD game on a flash cart. I just need to review the pin-outs and draw up a PCB

    http://n64.icequake.net/mirror/www.crazynation.org/N64/

    I know its possible to make one since the N64 Double slot adapter was an actual dev hardware.

    http://n64devkit.square7.ch/tools/parts.htm

    I just need to get better pictures of one.

    Edit: found some:

    https://ultra64.ca/gallery/kyoto-microcomputer-co-ltd-kµc/

    Not much to that board. I like the idea of using a 50 pin IDE connector to angle it.
    I think I can build one of these fairly easily and add the appropriate pin connections, it wont need the CIC chips or switch. Once prototyped and tested working, off to the pcb mills!
     
    Last edited: Jun 4, 2019
  5. abveost

    abveost Robust Member

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    Nice to hear v64s are getting rare. Makes me glad I haven't sold any of mine recently.
    Those links don't provide many details about the board or the things that plug into it but AFAIK the SRAM cart is for saves and doesn't use the same bus as the flash cart. I don't think that adapter does what you seem to think it does.
     
  6. Cybertronic

    Cybertronic Member

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    No of course not, I will need a different pinout. I will be building something similar, not an exact copy, but the fact of the matter is that the ext port where the 64DD connects and the cartridge connector up top share the same data lines back to the CPU.

    Not all 50 pins are used by the cartridge some are for the ext port and for communication with the cartridge. The ports mirror each other.

    This is why if you look on the pinout you will note that the power pin is exactly in the middle of the connector and there is a pin for two separate CIC chips. The 64DD has a CIC chip as does every game cartridge.

    The placement of VCC ports also mirror eachother as do the ground points this was done exactly for the purpose of communicating with the cartridge and the 64DD.

    The contents of a 64DD disk is essentially the same as a rom image found on a cartridge. This is why we have cartridge conversions of the Disk dumps.

    The whole 64dd unit itself is essentially one big magnetic cartridge with a reverse pinout.
     
    Last edited: Jun 4, 2019
  7. abveost

    abveost Robust Member

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    The cart and ext connectors being mirrors of each other has been well known for a long time. That's how all those copiers that sit under the console work. I just don't understand how a dev tool that doesn't do what you're trying to do helps you in any way. If you want something that lets you plug two carts into the top of an N64, and doesn't do what you want, you don't need an obscure dev device. Any region adapter that uses the CIC from a second card will do.
     
  8. Cybertronic

    Cybertronic Member

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    I don't want that exact Dev device I was merely using it's General design as inspiration for making my own dual cartridge adapter. As for region adapters, most of the time these adapters wouldn't have all the pins connected anyway. Just the ones necessary for cic lockout and they come with extra stuff like being able to transfer saves etc, I don't need all that.

    It's going to be easier just to design and build my own board besides, I can make more than one.

    Gotta keep it simple:

    1. 64DD Accessory cart + 64Drive Flash Cart connected to cartridge connector.
    2. 64Drive pretends to be a 64DD loads 64DD game and reads the accessory cart.

    No more need to figure out how to fit something on the bottom. No messing around with modifying expensive import adapters.
     
    Last edited: Jun 5, 2019
  9. abveost

    abveost Robust Member

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    That's exactly what I said. Neither the dual cart dev device or a region adapter will do what you want. As for design, personally I'd draw inspiration from just about anything except a bare PCB with a couple slots on it but whatever floats your boat I guess.
     
  10. Cybertronic

    Cybertronic Member

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    Ok, how would you design something that does not require any special chips or circuits and just needs to connect pins?

    I would want both cartridges to be up right that's two parallel slots on a board it's going to be horizontal and then it's going to need to go into the cartridge slot on the N64 it'll be perpendicular to it.

    I suppose I could go with a T configuration. A single baord with two slots facing up and one facing down between them connecting to a double ended "cartridge" but the that comes with it's own set of challenges.

    Keep in mind I don't have a factory for making fancy streamlined stuff. It's going to minimalist and functional and hand made. It's not some apple product. It doesn't have to be pretty, it just has to work.
     
    Last edited: Jun 6, 2019
  11. abveost

    abveost Robust Member

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    A three slot backplane with the outer two slots facing up and the inner one facing down would be a simple way to do what you're describing. And I'd absolutely do that first to make sure things work they way you're expecting. But I wouldn't use that design for much more. My personal preference would be to have the carts not be upright. I see top loaders as a waste of shelf space. I'd put the cart slots side by side for the same reason. The adapter would connect underneath because the console was designed specifically for that. There are mounting holes and screw holes there for it. Think a 1/3 height CD64 with two cartridge slots. If not ridiculously unfeasible I'd have the carts go in face up. The bottom of the console is relatively flat so the enclosure could be a simple box with a few holes in the top/front. I'm not worried about the riser because I could make an adapter to connect the EXT slot to a cart slot by laminating two (one and a half) PCBs of different thickness together. It's little more complicated, more work, and more expensive but it has a lot of advantages.
     
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  12. Bad_Ad84

    Bad_Ad84 The Tick

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    Id propose you have a pcb thick enough for the EXT connector, that goes though a cutout of a normal thickness PCB and soldered to that. rather than trying to attach the PCBS together (unless I am misunderstanding you).

    Vertical PCB of correct thickness into EXT, horizontal PCB of standard thickness with a cut out and pads to accomodate the vertical PCB. Solder it in and then you can have 2 right angle cart slots on the new PCB.

    But that all assumes you build a base/enclosure that houses it all, else all the weight is on the PCB/EXT connector
     
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  13. abveost

    abveost Robust Member

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    I was thinking along the lines of the adapter used inside the v64. At first the idea of having one board sticking up through another really rubbed me the wrong way. But after looking at it the vertical board wouldn't have to be very tall. You could also do a shroud/housing so any banging around during installation would be between the console and that instead of the PCB And using your own PCBs instead of an on the shelf socket you could bolt the whole thing down as securely as you want. And saves a socket. Might be the way to go.
    I was thinking a box made of PMMA with a few holes cut in it would work well as a base.
     
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  14. Cybertronic

    Cybertronic Member

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    I have no idea how I would affordably manage right angle cartridge slots. All the ones available are surface mount.

    This is good feedback though. I love brainstorming.
     
  15. Cybertronic

    Cybertronic Member

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    I had envisioned something like the TriStar 64 for the final version.
     
  16. abveost

    abveost Robust Member

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    You could convert vertical SMT slots to right angle using the same perpendicular PCB method BadAd described. Everything I have is straight and through hole I've already thought through various ways of rotating them. But you don't need to do that. That method would give you an edge card going into the console and a PCB you mount cart slots on on top of the console.
    Yeah, that's exactly what I was trying to avoid when imagining what it would look like. After looking at the cost in time/material for the enclosure there's a lot to be said for a small low profile top loading top mounting device though.
     
  17. Cybertronic

    Cybertronic Member

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    I don't think soldering two pcbs at angles to each other is a particularly reliable way to build something. It puts a lot of stress on the materials. Solder joints can crack. The board can delaminate. Its better to use connectors when attempting angles.

    So to do this safety, under system would require a card coming from the port with a cartridge slot and then another longer one with a edge connector to bring it out from under the console. It would require standoffs and an enclosure.

    I have a 64DD that I can either make a scan of and 3D print or make cast of it. I would rather do a laser scan just so everyone has it.
     
    Last edited: Jun 11, 2019
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  18. abveost

    abveost Robust Member

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    The idea initially made my skin crawl but after thinking it through I consider it a reasonable solution, certainly for connecting to the bottom of the console. If your sockets are SMT that's where solder joints are going to crack. Perpendicular boards could be bolted together with enough brackets to make them the sturdiest part of the unit. The 64DD doesn't use a card and socket to connect to the console. It's just a connector soldered to the board. I don't even think it's bolted down. If Nintendo is comfortable with it I guess I am. You have so many mounting points on the bottom that contact with the PCB should be next to nothing.
    If you're up for scanning the 64DD by all means do it. I wouldn't recommend printing it to use for this though. You could create a much better design from scratch in a fraction of the time. But it would be nice and a lot easier to take measurements from than the physical thing.
     
  19. Zoinkity

    Zoinkity Site Supporter 2015

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    You can go underslung, but you could also just use a splitter on the top port. There's several variants on that concept already, like the two and four board splitters in various 64DD development kits. That was originally something the 64drive's ultrasave was going to do but, well, it's a bit of a niche. Depending the draw you may need to provided it a bit of extra power.

    So long as no two devices uses the same addressing it shouldn't matter.
     

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