POLLING MECHANISM FOR TRANSFERRING CONTROL FROM ONE DATA PROCESSING SYSTEM OR SUBSYSTEM TO ANOTHER

摘要

A polling mechanism for use with apparatus for establishing and maintaining communication between a number of different types of subsystems. The apparatus includes a select line which interconnects all of the units in a closed loop. Control logic is provided at each unit in series with the select line. A bi-directional deselect line is provided interconnecting all of the units. A unit which has the poll (master unit) passes the poll by energizing the select line. A unit which does not wish to obtain the poll and thereby become the master unit, energizes the select line to the next unit in series in response to energization of the select line from the master unit. A unit obtains the poll (and becomes the master unit) by not energizing the select line to a next unit but by energizing the deselect which indicates to all units that the poll has been accepted.