Abstract: The apparatus detects error in transceivers of individual modules connected to a communication network, the network being a two-line network. The apparatus comprises a reference voltage source to output a first and second reference voltage value in response to a control signal. A controller controls a predefined sequence of steps in performing a test to detect the errors of the transceivers. A first and second comparator compares a voltage of the corresponding first and second line to a select first and second reference voltage as commanded by the sequence of steps of the test sequence.

Abstract: Data bases of a first and second input output processor (IOP), which are primary and secondary slave IOPs, respectively, are synchronized, and communications by a master controller is made only to the first IOP. Each IOP is executing the same tasks utilizing their own clocking systems. A method for periodically verifying that the first and second data base remain synchronized comprises the steps of sending a sync-verify type message to the first IOP. The second IOP eavesdrops on the communications, and when the second IOP recognizes that the message is addressed to the corresponding primary slave IOP, accepts the message. Upon detecting the message is of the sync-verify type by each IOP, operations by each IOP are suspended. A number is generated by each IOP of its own data base, the number being indicative of the contents of the information stored in the data base.

Abstract: Data bases of a first and second input output processor (IOP), which are primary and secondary slave IOPs, respectively, are synchronized, and communications by a master controller is made only to the first IOP. Each IOP is executing the same tasks utilizing their own clocking systems. A method for guaranteeing that the first and second data base remain synchronized comprises the steps of communicating a message to the first IOP to update the first data base. The second IOP eavesdrops on the communications, and when the second IOP recognizes that the message is to the corresponding primary slave IOP and that the first IOP has successfully received the message, accepts the message. The first IOP and the second IOP execute the received message. The master controller issues a status request type message to the first IOP, and then issues a status request type message to the second IOP.

Abstract: A system has at least one output device, the output device having a first set of output terminals connected to a corresponding field device. Each output device has a corresponding redundant output device having a corresponding first set of output terminals connected to the same corresponding field device as the corresponding output device. The output device and the redundant output device each have a second set of output terminals corresponding to the first set of output terminals, the second set of output terminals being connected to an apparatus for controlling the information outputted from the first set of output terminals. The apparatus comprises a plurality of switching elements, having a set of first and second contact points. Each of the second set of output terminals of the output device being connected to a corresponding first contact point, and the second set of output terminals of the redundant output device being connected to the corresponding second contact point.

Abstract: A controller of a control system, which operates as a master, has a slave input/output processor (IOP) connected thereto which communicates with at least one device of a predetermined type, and a backup slave IOP connected thereto of the same type as the slave IOP, the slave IOP operating as a primary IOP to the device. A method for providing backup to the slave IOP by the backup slave IOP comprises the steps of loading the backup slave IOP with the same data base as the slave IOP. The backup slave IOP eavesdrops on all communications from the controller to the slave IOP. When a write command is communicated to the slave IOP, the backup slave IOP taps the data from the bus and updates its data base. If the command is not a write command, ignores the communication. When a fault is detected by either the slave IOP or the backup slave IOP, the detection of the fault is communicated to the other IOP.

Abstract: Data bases of a first and second input output processor (IOP), which are primary and secondary slave IOPs, respectively, are sychronized, and communications by a master controller is made only to the first IOP. Each IOP is executing the same tasks utilizing their own clocking systems. A method for maintaining synchronization between the first and second IOP comprises the steps of transmitting a message addressed to the first IOP by the master controller. The first IOP receives the message for subsequent execution. Receipt of the message is acknowledged by a transmission back to the master controller the acknowledge message including a message number. The second IOP eavesdrops on the transmissions between the master controller and any of the IOPs on the network. Upon recognizing that the message is addressed to the corresponding first IOP and that the message is of a predetermined type, the second IOP receives the message for subsequent execution.

Abstract: A primary slave IOP, upon detecting an error, verifies the availability of a secondary slave IOP, and then sets an output control signal to indicate backup is requested. The primary slave IOP then takes itself out of being the primary. A secondary slave IOP, sensing that the output control signal from the other IOP has been set, assumes the roll of the primary slave IOP. A master controller, detecting an error with the primary slave IOP, interrogates the primary and secondary slave IOPs for a status input, and then arbitrates between the first and second IOP to determine the IOP that is to take on the primary role. Finally the master controller awards the more operational IOP the role of the primary slave IOP, thereby completing the failover operation.