An icon-based approach to system control development

The implementation of an icon-based manufacturing message specification (MMS) messaging system for system control in a manufacturing automation protocol (MAP environment) is described. The system was designed with a four-layer hierarchy. The top layer acts as a user interface and essentially provides a data manipulation service. The next layer invokes the appropriate firmware calls to manage the communication process. The third layer consists of the firmware that handles the actual transmission of data across the network. The lowest level is the actual network hardware. Twelve MMS services were implemented in order to provide the capability to carry out a typical control session. The system was tested using software that simulates the external communications of an MMS virtual manufacturing device. The LabVIEW MAP environment used imposed at least two limitations on the operation of the system. First, LabVIEW makes no provision for data structures; therefore, each parameter had to be passed from the MMS layer to the code VI layer as a variable of a specific data type. Second, LabVIEW provides no convenient way to maintain global variables throughout a diagram