Abstract: A programmable controller for operating a machine to carry out programmed functions includes a plurality of program processors. Each of the program processors is operable to execute simultaneously a different user control program that directs the operation of the machine to perform specific functions. Each of the program processors includes a memory for storing the user control programs and function chart data. The function chart data comprises a series of descriptor files each of which contain an identification of a user control program to execute, a transition condition that indicates when the execution of that user control program is to terminate, and which descriptor file is to be processed next as well as the program processors to process it. A mechanism is also provided to enable the program processors to execute other programs in as background tasks without adversely affecting the execution of the control programs.

Abstract: A programmable controller suitable for operating a machine to carry out a plurality of programmed functions includes a plurality of program processors each being operable to execute simultaneously a different control program that directs the programmable controller to operate the machine to perform specific functions. Each of the processors includes a memory having areas for receiving different priority level messages. Each area has an addressable location corresponding to each module in the controller that can send messages. A message may be an executable command or a pointer to an address block containing the message or message access parameters.

Abstract: 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.

Abstract: 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.