Abstract: A controller for executing an application program to process control information related to control elements includes one or more main processors that each run the application program; a time synchronization system that synchronizes the time clocks of the main processors; and a voting system that exchanges information between the main processors and compares the information received from the other main processors. In addition, the controller includes one or more rendezvous signals sent to and received by the main processors as well as a mechanism for updating the time clocks based on a clocking midpoint of all processor signals.

Abstract: The programming of programmable controllers and other sequential computing devices is facilitated by automatically generating an order for evaluating function blocks in a function block diagram and by automatically detecting any errors in a function block diagram which would adversely affect the generation of a unique evaluation order, such as illegal cycles, disconnected subnetworks, and/or wired-OR connections. The nodes affected by the noted errors are graphically displayed to the user, who then may use a graphical interface to edit the network until all the noted errors have been corrected. A recursive procedure analogous to a topological sort may be used to automatically generate a unique evaluation order.

Abstract: A majority-voted output circuit generates an output parameter which is the majority vote of its input parameters by series-parallel combination of four intermediate switches, each said switch being a Boolean function of the input parameters, and the circuit being arranged so that failure of any one switch does not affect the value of the output parameter. Alternate embodiments are provided which use "don't care" signals to allow the majority vote of less than the full complement of input parameters. The majority-voted output circuit is subjected to testing by stepped transitions of its input parameters (to test for failure of any of the four intermediate switches) and by forcing current flow through predetermined current paths (to test for failure of a particular electrical connection).