From Sega Retro
The XE-1 AP is an unusual analogue controller manufactured by Dempa. It is compatible with the Sega Mega Drive, but also with a number of other Japanese consoles and computers (some require extra adapters). The device was not released outside of Japan, though is revolutionary in many ways due to the fact it was released in 1989 - nearly a decade before analogue features of this nature became mainstream.
The controller has ten face buttons, four shoulder buttons, an analogue stick and an analogue slider (which can be rotated to suit the user). Many of these buttons exist as switches to maintain compatibility with the computers the controller supports. Others are turbo switches, or are simply not used in the majority of circumstances. There is also a switch to turn the controller back to "digital mode", allowing it to remain compatible with all games on each system (aside from computer games that do not support joysticks).
Several games support the XE-1 AP's analogue controls (including some first-party Sega releases):
Support for this controller largely remains in the westernised versions of these games, with the notable exception of After Burner III, which instead features 6-button support (the Japanese version is 3-button or analog only). It is not known whether this holds true for the two 32X games. It is also unknown if any home computer ports of Sega arcade games support the unit.