This is a brief description of our use of CapFast, Phase Three Logic's Hierarchical Schematic Design System, as a graphical control system configuration tool. Our control system known as EPICS (Experimental Physics and Industrial Control System), uses configurable functional blocks to implement control logic. These functional blocks are combined by the user to define complex control functions. As a hardware engineer, I saw the similarity to schematic representation of electronic circuits. I defined CapFast symbols which represent the primitive functional blocks supported by the control systems, and added ports and properties to allow connections and user configurable parameters. These symbols can be used in a CapFast schematic to define the desired logic.
Once the CapFast schematic defines the control logic, the information must be extracted from the netlist for use by the control system configuration software. I wrote a translator which extracts the information from an EDIF netlist of the schematic and writes a file which is readable by our configuration software. The translator flattens the hierarchy and represents the schematic as a network of primitive function blocks. I chose the EDIF format for compatibility with other commercially available packages, and to allow me to define the hierarchical naming rules.
The ability to use CapFast in defining our control logic is a great advantage, since graphical format is easy to understand, and in many cases, is the only documentation required. The robustness of the software, and the ability to handle large, hierarchical designs provides an impressive user interface for configuration tasks. The only requirement for using schematic capture packages in this way is that the control system be designed to be configurable using primitive functional elements that can be rendered as symbols, and connection information is simple enough to be represented in a netlist format.
Property information is entered to the control system, and many of the properties in the primitive symbols have a limited number of acceptable values (for example, input primitives support a limited number or hardware input cards). Users utilizes a flexible menu of CapFast which can be accessed from the property sheet at any time, not just when the symbol is first placed on the schematic.
The menus have been improved in the MOTIF version of CapFast so they are more closely allied with the menu structure of the PC Windows version. The flexibility to create customized menus remains for those users wishing to make some or all commands available from pull-down menus.
While some standards for commercial process control configuration graphics exist, the software is considerably less flexible and much slower than CapFast. Even though many of the commercial systems are based on many of the same concepts as EPICS, their editors do not have the power and flexibility of CapFast.
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