What do Expansion Ports C & D do on the Twin Fami?
I've heard that removing or leaving the cable that connects the two ports has no operational effect on the system. I don't have one, so I haven't look on where do the traces of the ports go.
digged out this old thread. I read here on Famicomworld (in other posts too) that it should not affect the operation mode of the Twin if you pull out the jumper cable between port C and D.
Today I tried this myself. Result is, FDS BIOS is acting funny, garbled sound and sometimes "Battery error" gets displayed. So, it seems that there is definitely a difference if cable is connected or not.
To my knowledge it is also possible to connect a FDS stick to port C. So my assumption is, that port C and D is actually the connection between internal RAM adapter and Disk System.
Has somebody more infos on this?
If the RAM Adapter would be disconnected from the Famicom it would just act like a Famicom without a cartridge. And if the disk drive is disconnected from the RAM adapter it would work like normal (but of course you can't feed it any disks).
But if the FDSStick works in it, it sounds like it's for connecting the disk drive?
Maybe it got several things in there.
"But if the FDSStick works in it, it sounds like it's for connecting the disk drive?"
Yeah, that's what I meant with
"So my assumption is, that port C and D is actually the connection between internal RAM adapter and Disk System."
According to https://3dscapture.com/fdsstick/ (bottom of page), the pins of Port C and the pins of the RAM adapter should be the same.
Maybe somebody else wants to try what happens if connection between port C and D is removed. At least we can confirm that it is not the same if the cable is connected or not.
Yeah it sounds like port C and D are just the Twin's version of the RAM Adapter cable plug and the disk drive port respectively (and external RAM Adapters or disk drives could be used with it this way if you have the right adapters), but then you say you get garbled sound and errors if you remove it. That's not what happens if the disk drive is removed on a normal Famicom, so it sounds like there's more to these ports.
Also RAM Adapter pin 8 and Twin pin 12 doesn't seem to be used in Loopy's diagram, which makes it sound like they are not analogues. But it might just be that this pin isn't needed by the FDSSstick.
according to the pinout of the RAM adapter plug, which I've found, I think port 8 (port 12 on Twin) is not used:
But I agree, something must be different. Otherwise I would not get the mentioned errors.
Aha it's used for motor power. Yeah that explains it as the FDSStick doesn't have a motor to power.