In the original design, the input was handled by a series of 5 buttons, these where connected to the PC via the parallel port. On the PC the port was scanned by a process called buttons it reported the button press to the player software. The button press was reported on button release, or after 2 seconds if the button was held down. Once the PC knew which button had been released, the appropriate action was taken.
The original button hardware was a silicone rubber keypad with 4 directional arrows, and an enter button, the enter button was used to enter the menu system the up and down arrows where used to control volume, or scroll through the menus according to mode, and the left and right buttons where tune down and up, skip back and forward or leave and enter submenus according to mode respectively.
The interim buttons where a membrane keypad and layed out in a similar fashion, their operation was similar and they where read in the same way.
The VFD display is a much larger device than the LCD panel it was replacing, there was a lot less room on the front panel for buttons, fortunatly the Grand Prix has steering wheel mounted remote control buttons that are usable for my application.
The frontpanel controller (see it's section) reads the analog values from the buttons, statistically determines which button was pressed and sends the message with the data in it.