What is the expansion port on the NES for?
It was rarely used, though on the Famicom it was used for many things, such as the 3-D glasses, Keyboard, Tape Drive, etc. The NES had two accessories which used the expansion port: The Miracle Keyboard Piano Teaching System, and The Baton Teleplay System [a modem device for the NES which offered head-to-head play on the NES and Genesis]. Teleplay, however, was never widely released.
