Abstract: Systems and methods of recording user actions on an industrial controller. When a user logs into an industrial controller (e.g., a stand-alone controller) changes made to the controller can be recorded by a logging component. The recorded information can be encrypted to ensure reliability of the information. The logging component can be periodically brought into communication with an aggregation component which can receive log entries from a plurality of controllers and their associated logging components, and compile the log entries into an aggregate log.

Abstract: Data is exchanged between two modules of a programmable controller by originator module writing the information in an interface memory in one of the modules and the recipient module reading the information from the memory. An initialization procedure is performed before any information is exchanged in that manner. The module containing the memory writes the size of the memory for reading by the other module. Sets of test data are stored in the memory by each module and checked by the other module to determine if data can be passed accurately between the modules in both directions. Then data identifying the type of one of the modules is exchanged to insure that the other module knows the type of module with which it is dealing.

Abstract: A communications network is comprised of master and slave stations. The master stations may receive a master token allowing control of the network for sending messages, and a solicit token that allowing the master stations to solicit other master stations for entry into the network. A master station receiving a solicit message answers with an acknowledgement signal and may immediately begin soliciting for successors. The slave stations receiving a solicit message may not accept the master token or the solicit token but must respond with a negative acknowledgement. Slave stations enter the network to respond to messages only. The use of slave stations allows for the implementation of simpler networks and improves network efficiency. The negative acknowledgement identifies the presence of the slave stations and allows detection of duplicate network nodes.

Abstract: Programmed digital equipment is utilized to generate three-phase pulse width modulated waveforms that are used in controlling an induction motor. A microprocessor is programmed to initialize conditions in the system, to perform a main task including the storage of converted analog signal, the checking of limits of motor motion and information fed back from the motor concernings its position, and the ramping of frequencies to change the position of the motor. A memory is provided for the programming which memory also contains tables that correspond to 90.degree. of each desired wave form. A single 90.degree. segment of each wave form is needed to generate all parts of each of the three phases. An analog to digital converter is utilized to convert analog information concerning gain, set point, dead band and feedback signal into digital signals which are stored and processed by the microprocessor.