Common items you passed up that turned rare when you wanted them

Not as crazy as a PERQ AGW3300 then. The monitor plinth contains a board called the multiplexer. It takes the serial lines from the keyboard and optional tablet, the quadrature and button lines from the mouse, etc, shoves them into a shift register (note, the serial data is not converted to parallel first), sent down to the main box as a fast data stream, then fed into another shift regiser, some outputs of which go to UARTs to accept the seiral data from the keyboard and tablet. The shift register is clocked fast enough that the serial data (1200 baud or something) is unmangled by this. Kersqueeble! Good luck. Having done this for somewhat simpler machines (although still complicated ones), I will say that it's a lot of work (expect to spend months doing it), but you get a very good understanding of the machine's hardware at the end. -tony