I plan to build a joystick for my MSX but I'm little confused on the purpose of Pin 8. The diagram at GameSX says it's function is "OUT(?)". That doesn't make a whole lot sense to me. What exactly is Pin 8 used for?

Switches should be connected between "OUT" and direction/button. In normal joystick you don't need to connect Ground or +5v at all.

Quote:

Switches should be connected between "OUT" and direction/button. In normal joystick you don't need to connect Ground or +5v at all.

So if "OUT" is connected to every button, does that make "OUT" the common ground?

I'm a moron when it comes to electronics. I'm still learning.

Quote:

Switches should be connected between "OUT" and direction/button. In normal joystick you don't need to connect Ground or +5v at all.

No!, this is WRONG!
OUT it is used to send a signal to a device, for example a circuit to have more than 2 buttons (like the Megadrive/Fmtowns/X68000),or the touch tablet.
You don't have to use it for a standard joystick, use only the inputs (U,D,L,R,B1 & B2) and GROUND as common.
It's just like the ATARI standard wiring, you only have 1 extra button.

maybe this is of any help?

http://www.faq.msxnet.org/connector.html#joystick

Some joysticks are not 100% MSX compatible. Joysticks designed for systems as Spectrum or Amstrad, use pin 8 as GND. They will work in MSX but some games (very few) will pull this pin up, thus showing +5v instead of GND.
Normally, using BIOS and correctly programing PSG, pin 8 is kept down (showing GND state) and these kind of joysticks will work fine.

pin 8 can be used with a PDL, this is a kind of joystick with a potentiometer.
The syntax is "P=PDL(x)" where x = 1 or 2

Ok, sorry... my bad... The joysticks I've opened have connected to OUT, but I think they might have been originally Amiga and C64 joysticks. How ever I've not experienced any problem with these in practise while I'm aware that it would be possible indeed change the OUT status as well as buttons statuses.