Abstract: An improved maintenance system and interface for use in a large-scale data processing system is provided. Within the data processing system, logic is partitioned into multiple logical groups. Each of the groups is associated with a bi-directional port, and each group may be intercoupled to other groups via the associated port. Within each of the groups, an internal condition detection circuit selectively monitors selected logic circuits to detect the presence of certain predetermined conditions or events. When an internal condition is detected, a notification is provided to the bi-directional port and broadcast over the interface to all other logic groups simultaneously. Each logic group further includes an external condition detection circuit interconnected to the respective bi-directional port whereby condition indicators are received from other logic groups as an external condition indicator.

Abstract: A digital communication bus upon which arbitration is distributed in a multiplicity of communicable interconnected bus interface logics supports unique signals to each associated on user device and upon the bus. Arbitration inhibiting signals, called inhibit request signals, allow any one(s) user device(s) to inhibit the new entrance, via requests, into arbitration of all other bus interconnected bus interface logics and associated user devices. Arbitration among bus interface logics already registering requests continues in priority order. Each user device may, via a signal called retract request, deregister, or cancel, requests previously registered at the associated bus interface logics to arbitrate for ownership of the bus. Each user device may, via a signal called stop bus, cause continuous interface logics while being precluded from recognition that arbitration should ever be won.