Keywords: PAC; Control; PLC; Standardization; ICPDAS; WinCon Since the ARC Group proposed the concept of PAC (Programmable Automation Controller), it has received widespread attention from the automation industry and end users as one of the most important development trends in the automation industry in recent years. This article attempts to explore the origins and key technologies of PAC, hoping to stimulate further discussion. Why Use PAC? The concept of PAC arose in response to the concept of PLC (Programmable Logic Controller). As a fast and reliable solution, PLC design meets the requirements of factories for operating environment and reliability, and its programming method is also very suitable for the thinking habits of electromechanical engineers. Therefore, PLC has dominated the field of automation control systems for more than 20 years since its inception. Current PLCs are no longer limited to logic control applications. Some new-generation large and medium-sized PLCs have relatively powerful floating-point data processing capabilities and relatively rich and complete communication interfaces, enabling them to complete today's systematic and complex automatic control technologies. In current automation applications, higher demands have been placed on automation control systems. The table below lists the changes brought about by these demands. [align=center][IMG=Latest Requirements for Automation Applications]/uploadpic/THESIS/2007/8/2007080115441793259W.jpg[/IMG] Figure 1: Latest Requirements for Automation Applications[/align] Although the PLC industry has noticed this trend and is providing greater application flexibility by applying PC technology to PLC products, directly providing OPC Server, WEB Server, and IEEE standard communication interfaces, etc. However, due to the limitations of traditional PLC's proprietary design, its interoperability and flexibility are poor (even for PLCs of the same brand), and it cannot fully meet user requirements: • Traditional PLCs cannot provide proactive event notifications; centralized system monitoring and management rely on proactive, periodic queries from the server host. • Due to the lack of real-time information, cross-PLC event processing is difficult, slow, and ineffective. • It cannot provide local, direct-processing scheduled control; scheduled control relies entirely on centralized processing by the server host, so system crashes result in immediate shutdown. • The system's architecture uses multiple platforms from different vendors; to integrate various dedicated buses, system connectivity relies on third-party OPC Servers or Gateways, making implementation challenging. • System upgrades require redesign costs and time, with unpredictable costs being too high. • Ladder diagram programming is designed on a case-by-case basis, making it impossible to completely replicate and apply to each project, thus hindering standardization and preventing cost reduction in engineering design. • Current automation systems have insufficient data capacity, making them inadequate for adapting to new application requirements. • Real-time synchronous remote data transmission is impossible, and connections with PDAs and mobile phones are difficult. • Remote data publishing via PC or third-party devices is required for web-based processing. What is PAC? Although PACs appear very similar to traditional PLCs, their performance is far more extensive. As a multi-functional control platform, users can combine and match relevant technologies and products to achieve specific functionalities based on system needs. Because they are developed on the same platform, PAC systems ensure the uniformity of all functional modules in the control system, rather than being a collection of completely unrelated components. Based on the opinions of industry experts, a PAC system should possess the following key characteristics and performance features: [align=center]Figure 2: Functional Definition of PAC[/align] • Provides a universal development platform and a single database to meet the needs of multi-domain automation system design and integration. • A lightweight control engine capable of implementing functions across multiple domains, including logic control, process control, motion control, and human-machine interface. • Allows users to run multiple applications with different functions on the same platform according to system implementation requirements, and allocates system resources among programs based on the design requirements of the control system. • Employs an open, modular hardware architecture to enable free combination and matching of different functions, reducing the overhead of system upgrades. • Supports the IEC-61158 fieldbus specification, enabling highly distributed factory automation environments based on fieldbus. • Supports de facto industrial Ethernet standards, allowing easy integration with factory EMS and ERP systems. • Uses established network protocols and programming language standards to protect user investment and facilitate data exchange across multi-vendor networks. Key Technologies of PAC Systems The emergence of this technology benefits from the development and progress in the field of embedded systems in recent years. On the hardware side, significant advancements include: embedded hardware system design, with the development of CPU technology being a prime example; the development of fieldbus technology; and the widespread application of industrial Ethernet. On the software side, this includes: embedded real-time operating systems; soft logic programming technology; and the development of embedded configuration software. These can be explained as follows: • Following Moore's Law, the latest high-performance CPUs achieve higher processing power while being smaller and consuming less power. This balances outstanding computing power with the stability and reliability that industrial users value most. This allows manufacturers to choose common, standard embedded system architectures for design, overcoming the limitations of traditional PLCs due to their proprietary hardware architectures, and enabling systems with richer functional prospects and greater openness. In existing PAC systems, the low-power, high-performance SOC (System On Chip) core processor is widely used. This includes CPUs using CISC architecture, such as the Mobile Pentium series, as well as CPUs using RISC architecture, such as the ARM and SHx series, and of course, some using MIPS CPUs. In summary, due to the comprehensive advantages of RISC CPUs in industrial control systems, systems using RISC CPUs currently account for the majority of control systems on the market. Alongside the development of CPU technology, there has also been significant progress in mobile storage technology, enabling the latest systems to obtain large-capacity data storage space at a limited cost, to meet the ever-increasing data volume requirements of new automation applications, while avoiding the risk of system crashes associated with using mechanical hard drives. ● After 14 years of debate, the IEC fieldbus standardization organization finally voted to adopt eight fieldbuses as the IEC 61158 fieldbus standard: FF H1, Control Net, PROFIBUS, INTERBUS, P-Net, World FIP, Swift Net, and FF's High-Speed ​​Ethernet (HSE). The finalization of the IEC 61158 fieldbus standard provides a standard to follow at the device and sensor levels in industrial control. Currently, in the field of industrial automation applications in mainland China, the more influential ones include: PROFIBUS, DeviceNET based on the CAN bus, LONWorks mainly used for building automation, and CCLink, which was not included in the IEC 61158 standard. However, because these eight fieldbuses use completely different communication protocols, achieving compatibility and interoperability is very difficult. A possible solution is to adopt internationally accepted standards such as Ethernet and TCP/IP, and make them conform to the requirements of industrial applications. This approach is most easily accepted and welcomed by users, integrators, OEMs, and manufacturers in most countries. However, to use Ethernet in industrial automation, the following four problems need to be solved: 1. Real-time issues. Because Ethernet uses CSMA/CD collision detection, the uncertainty of network transmission under high network load cannot meet the real-time requirements of industrial control. However, according to tests, in typical industrial applications, its peak load is around 500K, equivalent to 5% of 10M Ethernet or 0.5% of 100M Ethernet. Ethernet only exhibits noticeable latency when the load exceeds 40%. Meanwhile, various useful methods have been developed to improve the speed of Ethernet-related components and software, and to make data transmission and reception more reliable. The most promising solution is the IEEE 1588 Standard Precision Time Protocol (PTP). 2. How Ethernet meets field environment requirements. Ethernet connectors, hubs, switches, and cables are designed for office applications and do not meet the requirements of harsh industrial environments. To address the issue of stable network operation under extreme conditions in uninterrupted industrial applications, several companies have developed and manufactured DIN rail transceivers, hubs, and switches with redundant power supplies and robust DB-9 connectors, such as US-based KEON Control Systems and China's Dongtu Telecom. 3. How to obtain technical support for using Ethernet in industrial control. At the application layer of industrial Ethernet, four standards have gained widespread support and application: Schneider Electric's Modbus TCP/IP (1998) is currently the de facto standard for industrial Ethernet, enabling its extensive application at the sensor and device levels; Siemens' PROFINET (2001); Rockwell Automation's Ethernet/IP (2000); and Foundation Fieldbus's HSE (2000). 4. Ethernet and network security issues. Currently, various hardware and software technologies can effectively address network security issues. • General-purpose embedded real-time operating systems have made significant progress and are widely used. Traditional operating systems from Wind River Systems, such as VxWorks and PSOS, still hold a significant market share in the high-end market. Another notable trend is Microsoft's Windows CE, which, after releasing its .NET version, effectively solved the hard real-time problem and gained popularity due to its low price and broad customer base. As a representative of open-source software, Linux has also launched its embedded version, gaining favor with some specialized application customers and small and medium-sized manufacturers due to its advantages in cost, openness, and security. The development of soft logic programming languages ​​conforming to the IEC-61131-3 standard has effectively integrated the accumulated programming techniques of traditional PLCs, enabling electromechanical engineers to implement their control logic using familiar programming methods on PC-based systems. On the other hand, engineers can also use high-level languages ​​such as VB.net, EVC, VC#, and JAVA to implement complex algorithms or communication programming on PAC systems. Currently, the IEC-61131-3 standard has implemented the basic layer (including code bodies and variables), is working on the carrier layer (including functions and function blocks), and will eventually implement the entire compilation layer (application program). This effectively improves interoperability between devices from different vendors and reduces the cost of system upgrades. ● Regarding the human-machine interface (HMI), many software logic development tools also provide HMI development kits, such as ISaGRAF, Micro Trace Mode, and KW MultiProg. For more advanced needs, some professional SCADA/HMI software vendors also offer software packages for embedded system development, such as KingView (embedded version) from KingSCADA and Indusoft. Currently, mainstream PAC systems Several manufacturers currently offer products that conform to the characteristics and performance defined by PAC, including representative examples such as: GE Fanuc's PACSystems RX3i/7i, NI's Compact FieldPoint, Beckoff's CX1000, and ICP DAS's WinCon/LinCon. Among them, GE Fanuc's PACSystems RX3i/7i CPUs use Pentium III 300/700MHz processors, with WindRiver's VxWorks operating system. The RX3i uses the VME64 bus, while the RX7i uses the CompactPCI bus. NI's Compact FieldPoint CPU will soon be upgraded to a Pentium IV-M 2.5GHz processor, featuring the integration of LabVIEW, a widely used development platform in the test and measurement field. Beckoff's CX1000 CPU uses a Pentium MMX 266MHz processor, with Windows CE .NET or Embedded Windows XP operating systems. ICPDAS's WinCon/LinCon CPUs use a StrongRAM 206MHz processor; WinCon uses Windows CE .NET, while LinCon uses Embedded Linux. [align=center][IMG=WinCon-8000]/uploadpic/THESIS/2007/8/20070801155815592117.jpg[/IMG] Figure 3: ICPDAS Smart PAC – WinCon-8000[/align] The image above shows ICPDAS's WinCon-8000. We will use this as an example to illustrate the functions and characteristics of the current generation of programmable automation controllers: • I/O Modules: WinCon supports three types of I/O modules: serial connection, Ethernet network connection, and parallel (Build-in I/O) connection. Each of these three architectures of I/O modules has its applicable scenarios. Choose the type that best suits the planned signal response speed. Compared to PLC I/O modules, its analog I/O has higher accuracy and sampling speed, while its procurement cost is lower. In addition, WinCon's network I/O will gradually support CAN (Control Area Network) bus and ICP's own FRNet. Through communication protocols such as Modbus/RTU, CANOpen, and DeviceNet, it can connect with ICP's I-7000, I-8000, and other brands' CAN I/O. FRNet, on the other hand, adopts the advantages of PLC architecture, using the Token Ring method, which does not require software protocols. It can scan all I/O points within a fixed time and then communicate with the main control layer through Dual-Port RAM. [align=center][IMG=WinCon Application Architecture]/uploadpic/THESIS/2007/8/200708011600227892227.jpg[/IMG] Figure 4 WinCon Application Architecture[/align] • Soft PLC: Provides software packages for Soft Logic PLCs such as ISaGRAF and Micro Trace Mode, which can fully execute the ladder diagram program functions of PLCs. The usage involves first editing and designing the ladder diagram application on a PC, then downloading it to WinCon-8000 for execution. This means it can be used as a PLC, and it also offers several functions that a traditional PLC cannot, creating a PLC Plus effect: • SCADA System: Provides a suite of monitoring systems including Embedded View, Indusoft Web Studio, and AdAstrA Embedded HMI. Since WinCon provides the execution version, the desired monitoring screen is designed on the PC first, then downloaded to WinCon for execution. These monitoring systems also have various PLC communication modules and OPC Client drivers, so in addition to communicating with WinCon's own I/O modules, they can easily communicate with other PLCs. • OPC and Modbus Support: WinCon provides two data communication methods: OPC and Modbus, enabling data exchange of I/O signal values ​​with external systems. These communication methods are two major communication standards in the industrial control industry, so system integration can also be standardized. For example, previously, any program connecting to a PLC to read and write relevant signal points had to design its own communication driver, which required familiarity with the different communication methods and signal arrangements of various PLCs, making system design extremely difficult. Now, based on the two communication standards mentioned above, many components are available on the market. Everything can be handled with just one WinCon. ● SQL Database: This function is crucial. This is a standard relational database, on par with Windows SQL Server. General control systems, limited by hardware architecture, can only focus on signal point processing and cannot handle large amounts of data. However, the development of PC hardware and software systems has made this basic system robust and cheaper, enabling the storage and processing of large amounts of data, expanding into many new application areas. Examples include: recipe sheets, production work orders, product quality records, operation records, alarm records, work procedures, video files, audio files, equipment operation records, and various forms of data recording. The more detailed the data, the more opportunities to utilize it, creating many new functions; the more transparent the information, the more precise the control, while also reducing human error rates and extending to many new application methods. • Network Connection iPush: This feature opens a convenient door to networking, allowing application system users to operate without needing to understand the complex network processing procedures behind the scenes. Previously, designing network systems required knowledge of TCP/IP, Socket, and the 7-layer architecture of network communication protocols. Designing network communication programs then required advanced programming skills such as traffic volume, communication speed, Socket API usage, and mastering communication timing. Furthermore, there were various communication methods to choose from, such as SMS, voice notifications, image transmission, email, messages, active broadcasting, majority or individual notifications, communication frequency, and one-way or two-way communication. Finally, the choice of receiving end was also diverse, including monitoring systems, OPC servers, Excel spreadsheets, PDAs, mobile phones, and Internet browsers. Now, all of the above can be handled by iPush, as shown in the figure below. [align=center] Figure 5: iPush implements real-time active synchronous communication based on TCP/IP[/align] • Development Tools: For those who want to develop their own programs, there are various tools available, such as Visual Basic .NET, Visual C#, and Embedded Visual C++. Simultaneously, various interface APIs are available for integrated design. These include: I/O control DLLs, iPush components, SCADA System API, SQL Server API, Modbus Protocol DLL, OPC interfaces, etc. In other words, the required connection interfaces can be obtained from various functional levels, thus forming a completely integrated system. Satisfactory integration can be achieved from any approach. Therefore, users can confidently design programs with unique functions and then integrate them into the existing system suite to create a new application system. Future Outlook In the foreseeable future, standardization, openness, interoperability, and portability will be key characteristics of automation products that users are most concerned about. PAC systems, which combine the advantages of IPC and PLC, will inevitably become the mainstream control system. Automation suppliers will launch more controllers and new functions suitable for customized applications in various fields in the coming years to meet the broad and ever-growing demands.