The National Institute of Standards and Technology (NIST) is working to improve the information technology (IT) security of networked digital control systems used in industrial applications. This effort is being carried out through the Process Control Security Requirements Forum (PCSRF), an industry group organized under the National Information Assurance Program (NIAP). The PCSRF is working with security professionals to assess the vulnerabilities and establish appropriate strategies for the development of policies to reduce IT security risk within the U.S. process controls industry. The outcome of this work will be the development and dissemination of best practices and ultimately Common Criteria, ISO/IEC 15408 based security specifications that will be used in the procurement, development, and retrofit of industrial control systems. In support of this work this paper addresses the computer control systems used within process control industries, their similarities, and network architectures.A generic set of networking system architectures for industrial process control systems is presented.The vulnerabilities associated with these systems and the IT threats these systems are exposed to are also presented along with a discussion of the Common Criteria and its intended use for these efforts. The current status as well as future efforts of the PCSRF are also discussed.

General-purpose microprocessors are increasingly being used for control applications due to their widespread availability and software support for non-control functions like networking and operator interfaces. Two classes of real-time operating systems (RTOS) exist for these systems. The traditional RTOS serves as the sole operating system, and provides all OS services. Examples 1 include ETS, LynxOS, QNX, Windows CE and VxWorks. RTOS extensions add real-time scheduling capabilities to non-real-time OSes, and provide minimal services needed for the time-critical portions of an application. Examples include RTAI and RTL for Linux, and HyperKernel, OnTime and RTX for Windows NT. Timing jitter is an issue in these systems, due to hardware effects such as bus locking, caches and pipelines, and software effects from mutual exclusion resource locks, non-preemtible critical sections, disabled interrupts, and multiple code paths in the scheduler. Jitter is typically on the order of a microsecond to a few tens of microseconds for hard real-time operating systems, and ranges from milliseconds to seconds in the worst case for soft real-time operating systems. The question of its significance on the performance of a controller arises. Naturally, the smaller the scheduling period required for a control task, the more significant is the impact of timing jitter. Aside from this intuitive relationship is the greater significance of timing on openloop control, such as for stepper motors, than for closed-loop control, such as for servo motors. Techniques for measuring timing jitter are discussed, and comparisons between various platforms are presented. Techniques to reduce jitter or mitigate its effects are presented. The impact of jitter on stepper motor control is analyzed.

This report describes an interpreter which reads numerical control code and produces calls to a set of canonical machining functions. The interpreter is a software system written in the C++ programming language. The output of the interpreter may be used to drive 3-axis to 6-axis machining centers. Input to the interpreter is RS274 code in the dialect defined by the Next Generation Controller (NGC) project, with modifications. The interpreter may be compiled as a stand-alone computer program or may be integrated with the NIST Enhanced Machine Controller (EMC) control system. Input can come from a file or from a user typing on a computer keyboard. Output commands can either be printed for future use or be executed directly on a machining center. The report includes a full description of the RS274/NGC input language and the canonical machining functions called by the interpreter. It is a complete users manual.

This paper describes an experiment in building and running two STEP-NC interpreters for milling operations: one using ISO 14649, the other using AP 238 of ISO 10303. Both use STEP part 21 exchange files as input and call low-level machine control functions. Both include tool path generators and have sufficient functionality to execute the first example program at the end of part 11 of ISO 14649. The objectives and results were: (1) to determine if ISO 14649 and AP 238 contain sufficient information to run a machining centre (yes); (2) to determine whether AP 238 faithfully remodels the information in ISO 14649 for the functionality that was implemented (yes); (3) to determine whether real-time interpretation of STEP-NC is feasible (yes); (4) to determine the burden on systems programmers to build a STEP-NC interpreter (heavy); (5) to determine how interpretation time varies with file size (linearly for both interpreters); and (6) to compare the speed with which the two formats can be interpreted. Using currently available software tools, ISO 14649 can be interpreted significantly faster, but both interpreters are so fast that interpretation time is negligible compared with running time.

STEP-NC is the result of a ten-year international effort to replace the RS274D (ISO 6983) G and M code standard with a modern associative language. The new standard connects CAD design data to CAM process data so that smart applications can understand both the design requirements for a part and the manufacturing solutions developed to make that part. STEP-NC builds on a previous ten-year effort to develop the STEP standard for CAD to CAD and CAD to CAM data exchange, and uses the modern geometric constructs in that standard to specify device independent tool paths, and CAM independent volume removal features. This paper reviews a series of demonstrations carried out to test and validate the STEP-NC standard. These demonstrations were an international collaboration between industry,