Why $4017.D0 is present in famicom's EXP port?

Discuss hardware-related topics, such as development cartridges, CopyNES, PowerPak, EPROMs, or whatever.

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krzysiobal
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Why $4017.D0 is present in famicom's EXP port?

Post by krzysiobal »

The famicom has both joypads hardwired, using $4016.D0 and $4017.D0 which is push-pull output, not open collector, so why $4017.D0 is present in the expansion port if nothing can use it unless joypad is unplugged?
The only thing that comes to my mind is sniffing the $4017.D0 (like for a device that would record the input movements and then play it back on the $4017.D1 if game ORs $4017.D0 and $$017.D1.
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Ben Boldt
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Re: Why $4017.D0 is present in famicom's EXP port?

Post by Ben Boldt »

I never understood that either and especially why on earth is expansion audio not included in 72-pin connector... Such a horrible decision that prevented works of art we will never know. I suppose we never experience audio crackling as we jiggle the cart though. I am just really frustrated they left that out, probably all because they want those EXP pins free to make gambling machine attachment... And use up other pins for lockout and strange 2.50mm finger spacing. WHY do they choose 2.50 when Famicom is already correctly 2.54mm... So many terrible decisions but we learn to live with it.
lidnariq
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Re: Why $4017.D0 is present in famicom's EXP port?

Post by lidnariq »

My best guess is that they originally intended to only have one controller tethered, and player 2 only via the expansion port.

But the microphone gets in the way of that hypothesis, so I'm really not sure.
Ben Boldt wrote: Tue Nov 03, 2020 10:41 am I am just really frustrated they left that out, probably all because they want those EXP pins free to make gambling machine attachment.
EXP pins were definitely intended for the Famicom Disk System.
And use up other pins for lockout and strange 2.50mm finger spacing. WHY do they choose 2.50 when Famicom is already correctly 2.54mm.
Also deliberate, to impede unlicensed game manufacturers. Yeah, the "metric inch" spacing is one of those things that you only have to notice once, but before the internet you might not have looked closely enough before getting your PCBs made, and then you'd have a bunch of unusable PCBs.
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krzysiobal
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Re: Why $4017.D0 is present in famicom's EXP port?

Post by krzysiobal »

Heh exactly, few years ago I was making 72 to 60 pin adapter. Didn't have the source of 72 sockets, so butchered old 62 pin isa connecctor. It did not have enough pins so I came up with the idea of spliting it in half and skipping the center pins because they are never used. Hardest part was to split it in the L-shape and not to break any of the pins. Didn't even knew at the time it is different pitch.
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Ben Boldt
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Re: Why $4017.D0 is present in famicom's EXP port?

Post by Ben Boldt »

lidnariq wrote: Tue Nov 03, 2020 11:00 am
Ben Boldt wrote: Tue Nov 03, 2020 10:41 am I am just really frustrated they left that out, probably all because they want those EXP pins free to make gambling machine attachment.
EXP pins were definitely intended for the Famicom Disk System.
I did not know that nor had the thought ever crossed my mind. It all makes sense now, even the FDS injecting its audio up into the expansion port. I am trying to imagine what that would have looked like.
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aquasnake
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Re: Why $4017.D0 is present in famicom's EXP port?

Post by aquasnake »

Shared with Joypad 2, it can be connected with digital level input, such as tape driver, or microphone input

You can also define an address from $4020 to $5fff instead of port $4017, and expand the function through the cartridge slot, or install an earphone jack on the cartridge board.

That's similar to the pec-586 educational computer.

Based on the reliability and aesthetics, the joypad interface/expansion port solution is better than the cartridge adapter.
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krzysiobal
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Re: Why $4017.D0 is present in famicom's EXP port?

Post by krzysiobal »

aquasnake wrote: Sun Jun 13, 2021 11:47 pm Shared with Joypad 2, it can be connected with digital level input, such as tape driver, or microphone input

You can also define an address from $4020 to $5fff instead of port $4017, and expand the function through the cartridge slot, or install an earphone jack on the cartridge board.

That's similar to the pec-586 educational computer.

Based on the reliability and aesthetics, the joypad interface/expansion port solution is better than the cartridge adapter.
What this post has to do with the question asked in topic?
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aquasnake
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Re: Why $4017.D0 is present in famicom's EXP port?

Post by aquasnake »

What this post has to do with the question asked in topic?
I just construed that you were asking what it exists for.

I replied the possible useage, but I was not sure about the original purpose of the designer. And also suggested that you can design another port on the cart to implement the functions if you need
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