Specifies the system ID number of the system to be added to the
  display.  The system is assumed to be removed from the display
  via the REMOVE SYSTEMS/ID or /NODE commands.  To specify a
  hexadecimal value as the ID number, precede the value with %X.
  Optionally, ALL can be specified to restore all SYSTEMS that were
  previously removed via the REMOVE SYSTEMS/ID or /NODE commands.

  Format:  ADD SYSTEMS/ID=(system-ID[,...])
           ADD SYSTEMS/ID=ALL

  If only one system ID is specified, the parenthesis can be omitted.

  Examples:  ADD SYSTEMS/ID=101
             ADD SYSTEMS/ID=(206,%XF2A)