摘要:
An industrial control system employs a primary and secondary controller each having a processor and an I/O data table. Updating of the secondary processor's I/O data table is accomplished synchronously with execution of the program in the primary processor at a particular point in the program. A tracking of changes in the I/O data table of the primary processor is used to transmit only changes in the I/O table to the secondary processor thereby avoiding undue interruption of the executing program while preserving synchronicity.
摘要:
An active programmable controller services I/O racks which contain circuits that interface with sensing devices and operating devices on a machine being controlled. A back-up programmable controller monitors this I/O data to maintain a current I/O image table in its memory. Other status data is coupled to the back-up controller from the active controller through a peer-to-peer communications link. If a malfunction occurs in the active controller, the back-up controller is signaled to switch to the active mode in which it assumes control of the operating devices on the machine being controlled.
摘要:
A redundant industrial controller system has a primary controller backed up by a secondary controller and recovers from a power loss by analyzing the state memories of the controllers to reach a determination of which controller would best be suited to assume primary control status without resorting to arbitrary tie-breaking procedures or race conditions. The rules and their inputs are applied by both controllers which independently make the determination as to which controller should be the primary controller.
摘要:
A method and apparatus for providing multitasking of a plurality of requests queued as a list in a single task of an industrial controller, each request including one or more separate segments. State information relating to each request being minimal at the end of each segment. The method processing the requests on a round-robin basis, interrupting each request only at the end of each segment so as to minimize the memory required to store the state information.
摘要:
A communication module has a backplane interface circuit that enables the module to communicate with other components of the programmable controller, and has a network interface circuit which sends and receives messages via a serial communication link. A memory within the module stores a designation of a starting time, a designation of a length of a message repeat interval, and a file of message information. A clock circuit determines when the starting time occurs and thereafter determines the expiration of each successive occurrence of the message repeat period. A control mechanism responds to the clock circuit determining an occurrence of the starting time or determining an expiration of a message repeat interval, by operating network interface circuit to transmit a message, that contains the message information, over the serial communication link.
摘要:
A programmable controller governs the operation of a piece of equipment by executing machine language instructions compiled from a ladder diagram type control program. The control program as stored in the controller includes not only compiled machine language instructions, but also a tokenized version of the source code from which certain machine language instructions were compiled. The source code is provided only for those portions of the machine language program which cannot be easily decompiled to produce the corresponding source code. This program storage facilitates subsequent editing of the stored program via a terminal connected to the programmable controller. During the editing process, the original ladder diagram can be reconstructed from a combination of the machine language instructions and the tokenized version of the source code. In doing so, the machine language instructions, which have a one-to-one correspondence with the source code instructions, are decompiled using conventional techniques. However, the tokenized version of the source code is used to recreate the portions of the ladder diagram for which each machine language instruction does not have a unique one-to-one correspondence with a source code instruction. This program storage technique enables the control program to be easily edited using the version stored in the programmable controller without requiring access to the original source code from which the program was compiled.
摘要:
In a communication network wherein a master station periodically polls a number of remote stations to determine whether or not each remote station has data to transmit to the master, each of the remote stations is assigned to one two groups. One of the groups is designated as priority stations which commonly have very urgent data for the master station. The group of non-priority stations is sequentially polled for messages to be sent to the master station. The polling of the group of non-priority stations is periodically interrupted so that the master station may poll each of the stations in the priority group to determine if they have messages to send. Upon the completion of the polling of the priority stations, the polling of the non-priority stations is resumed. Periodically a time period occurs for inactive stations to join one of the two groups of stations on the network. This method permits stations that typically have high priority data, to transmit that information more frequently than would be possible if only one polling group of stations existed.