DDB is hooked up to the NMI, which can be generated from the
keyboard with a 3 key combination.

From next docs via google:

  "To generate an NMI on a keyboard that has only one Command key, use
  Command-Left Alternate-~.  (Hold down both the Command key and the
  leftmost Alternate key and press the ~ key.  Do not press the Shift
  key.)  To generate an NMI on a keyboard that has two Command keys,
  use Command-Command-~.  (Hold down both Command keys and press the
  key at the upper left of the numeric keypad.)"

  "To reset the CPU, hold down the Command and Alternate keys at the
  lower left of the keyboard, and press the * key on the upper right
  of the numeric keypad.""

Darrin