IEEE 488 bus (GPIB - General Purpose Interface Bus) 
  Developed by HP (1960s)for electronic instruments and scientific devices.
  Standardized as IEEE 488.
    Updates 1975, 1987, 1989, 2004
  
  Parallel protocol.

  15 devices allowed on bus (with proper signal boosting 31 possible)
    Address hardwired on each device (switches).

  Data lines used for data addressing, data transfer, and device control.  
  
  Control/status (handshaking) lines used for controlling data transfer.

  No clock of any kind, IEEE 488 is asynchronous.
    Handshaking provides all signal confirmation and state advancement.
    Slowest device set bus speed.

    * Some of the handshaking signals had maximum response times. 

  Initial arbitration done by user, 
    User selects a controller for a particular task.

  Any device can be controller, talker, and/or listener.
    Data direction determined by becoming talker.

  Only one controller can be in control at a time.
    Controller can pass on control to another controller.
    Controller does not have to be talker/listener.
      Talker sends data.
      Listener receives data.   

  Controller selects a talker 
    By specifying their device addresses on data bus in combination with
    the appropriate control/status handshaking signals.

  Talker then selects a listener
    by using similar handshaking.

  1 MB/sec - newer version up to 8MB/sec.
    But slower was not uncommon.