The Commodore CD32 controller was intended for the CD32 game console released in the mid ’90. This controller use a serial shifting method to read its extra buttons via existing pins/buttons of the standard Atari style controller pinout scheme. This is no surprise for Commodore to use this technique in order to be backward compatible with the Atari standard.  In fact, this controller would work on an Atari 2600/Commodore 64/Amiga using only its red button for trigger.

Controller pinout