IEEE 488 bus lines
  8 Data lines
    Used for address, data, and some control information.
    Single-ended signaling.

  8 Ground lines
    Used to balance electrical charges.

  5 Interface management lines (control)
    Used in combination with each other and handshake lines for specific tasks.
    * Lines use pull-up or pull-down logic. Certain states require unanimous
      agreement. (Any device can veto). 

    ATN - asserted by controller to indicate address or control data from
      controller on data lines.  Similar to !FRAME on PCI bus.

    EOI (end or identity) - by talker to indicate last byte of transaction.
      Or by controller to perform polling - type of interrupt handling  
        initiated by controller.

    IFC (interface clear) - by controller to reset or initialize devices.

    REN (remote enable) - used by controller to transfer control to 
      different device.
  
    SRQ (service request) - an interrupt request by any device. Once received,
      controller must poll all devices to find requester.

  3 Handshake lines
    !NRFD not ready for data - by listener.

    !NDAC not data accepted - by listener,
      data or control info still being read off bus.

    !DAV data valid - by talker,
      indicates that good data or control info on bus.

The original protocol describes physical and electrical parameters. It did
  not define the specific control/hand-shaking sequence for communication. That 
  was left to the controller and device manufacturers.

Later updates did describe a task communication language sent on data lines.