
Suppose you're building a circuit to process scancodes from a PS/2
keyboard for a game. Given the last two bytes of scancodes received, you
need to indicate whether one of the arrow keys on the keyboard have been
pressed. This involves a fairly simple mapping, which can be implemented
as a case statement (or if-elseif) with four cases.

  Scancode[15:0] | Arrow key
  16'he06b       | left arrow
  16'he072       | down arrow
  16'he074       | right arrow
  16'he075       | up arrow
  Anything else  | none

Your circuit has one 16-bit input, and four outputs. Build this circuit
that recognizes these four scancodes and asserts the correct output.

module TopModule (
  input [15:0] scancode,
  output reg left,
  output reg down,
  output reg right,
  output reg up
);

