Abstract: A Unique Phase Difference Measuring Circuit which measures the phase difference between a reference pulse train and a slave pulse train. The present invention includes delay lines that determine the phase difference between the pulse trains which can be read directly by a microprocessor.

Abstract: An address generator which provides addresses for machine storage and software retrieval of computer status information. A counter is used to generate address signals in a descending order until it is disabled by a computer during alarm conditions. Under such conditions the counter provides a bias address for referencing the most recent status word. A gating circuit gates computer generated address signals to an adder circuit during the alarm conditions. The adder circuit adds the computer generated address signals to the counter generated bias signal to provide address signals which reference physical storage locations in a memory.

Abstract: A synchronizing circuit synchronizes the asynchronous ready signals for two separate microprocessor subsystems that are running synchronously as part of a fault tolerant computer system. Duplicated synchronization circuits, confined in a master-slave arrangement, are utilized with the duplicate microprocessors. Storage and gating circuitry are used to provide the precise timing signals required for such synchronization.

Abstract: A synchronizing circuit that synchronizes the non-maskable interrupt (NMI) input signals of two separate microprocessor subsystems that are running synchronously as part of a fault tolerant computer system. This circuit enables both microprocessors to detect and respond to an error condition at an identical point in their relative bus timing sequence even though there may be a real time skew between the bus timing of these two subsystems. Storage and gating circuitry are used to provide the precise timing signals required for such synchronization.

Abstract: A memory access selection circuit including a microprocessor, address, data and control multiplexers, a random access memory, storage circuits and related logic circuitry. This circuit allows both an external processor and the microprocessor to receive data from and transmit data to, the random access memory. The microprocessor controls access of the external processor to the random access memory by controlling and monitoring the multiplexer and storage circuits. This prevents erroneous data, address and control signals from appearing at the memory when switching between the microprocessor and the external processor as sources to the memory.