Abstract: A programmable controller of the type used to solve relay ladder diagrams is taught. The programmable controller includes a memory into which is placed a digital representation of the rungs of the ladder diagram. The disposition of various switches and coils are periodically sampled by other portions of the programmable controller and stored in other memory locations. At appropriate times between sampling intervals, the various memory information are combined and provided to a relay line solver which comprises part of the programmable controller. The sequence in which the information is provided to the relay line solver is determined by the sequence of ladder diagram entry into the memory by the programmer. The sequence of entry is determined during the entry process in a real time frame by apparatus within the programming panel which utilizes the interconnection of contact information which is provided by the operator in the manipulation performed.

Abstract: A programmable controller of the type used to solve relay ladder diagrams is taught. The programmable controller includes a line solver which has as a part thereof relatively simple low capacity shift register memories for storing interim intercontact node power status information without necessitating the use of a separate large capacity remotely located memory within the programmable controller. Because of the presence of left and right node shift registers as storage devices in the line solver, the line solver may be used to provide an ultimate solution for even a complex rung of a ladder diagram by utilizing only one line solver operation per each entered contact or device. No extra line solver operations are required for intercontact connections nor for transferring information between the line solver and the main memory on an interim solution basis other than to take input information from the main memory and to provide final output information to the main memory.

Abstract: A programmable controller of the type used to solve relay ladder diagrams is taught. The programmable controller includes a memory into which is placed a digital representation of the rungs of the ladder diagram. The dispositions of various switches and coils are periodically sampled by other portions of the programmable controller and stored in other memory locations. At appropriate times between sampling intervals, the various memory information are combined and provided to a relay line solver which comprises part of the programmable controller. The relay line solver updates the status of the relay ladder diagram and restores the updated information in a memory. This memory is used during the sampling intervals to change the status of output devices.