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N64 Breakout board for N64 Expansion Port (xPosted from AG)


New member
Original poster
Jun 4, 2019
AG Join Date
May 27, 2013
Not wanting my original thread to die with AG I am cross posting it here and hopefully with continued developments.
Original post: https://assemblergames.com/threads/breakout-board-for-n64-expansion-port.71012/#post-989688

Cybertronic said:
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.

Cybertronic said:
josiahgould said:
Spitballing here... Could you somehow use a GameShark as a passthrough and access the cartridge attached to the back?

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

abveost said:
Whatever you do will require "custom hardware". If you only need one borrow the adapter inside a v64.
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


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


I just need to get better pictures of one.

Edit: found some:


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!

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