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Hilscher03141technical articles

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This is suitable for new control generations without fieldbus connection or for controlling the periphery via PC via Ethernet "NETHOST" gateway by Hilscher as a bridge between fieldbus and Ethernet. Controlled via native TCP / IP, the device supports the full scope of a fieldbus PC card. It can be controlled remotely and transmits cyclic and acyclic data as well as alarm and diagnostic messages.

Real-time Ethernet systems are well established, but not all of the required capabilities are needed. Simple Ethernet meets the basic communication requirements, can be connected to Gateway implement the connection to the fieldbus. Nethost integrates the fieldbus with little effort and allows remote control as if the interface were available locally. "The control provider using the gateway could then follow the slogan: 'Controls 1000 Profibus inputs and outputs in one millisecond without its own Profibus connection,' explains Armin Beck, product manager for gateways at Hilscher Gesellschaft für Systemautomation mbH, the utility of the device. "For design reasons, the controller would only have an Ethernet interface and still be able to address Profibus I / O peripherals." Because Nethost simply hosts the missing fieldbus interface as an Ethernet node, thanks to simple TCP / IP Protocol and the high transmission speed of 100 Mbit / s an adequate replacement for the previously integrated fieldbus solution.

Bring Ethernet and fieldbus in line

Hilscher03142The potential for savings in the construction of modern production facilities through the use of Industrial Ethernet is high. Advantages include, for example, the continuity of the communication system, the use of a uniform cabling standard, the simple redundancy capability for avoiding failures and short cycle times with high deterministic data transmission.

To the chagrin of the mechanical engineer, however, six Industrial Ethernet systems have established themselves on the market. Introduction and support of each system require investment. "The new performance data is expensive to buy," Beck continues, asking: "Does it always have to be the industry-standard Ethernet?" While maintaining the fieldbus, the simple Ethernet of the office world is sufficient. In fact, it may make sense to continue to use the existing fieldbus potential. For example, hard real-time capability is only required in motion control applications. In more than 90% of all applications, it is irrelevant. The low cycle times of the real-time Ethernet systems under 1 ms are rarely needed.

So if machine segments have proven themselves in fieldbus design for years and now need to be coupled to Ethernet and remotely controlled, Nethost qualifies for this purpose with its low latency of 1 ms and support for simple TCP / IP. The bandwidth of the 100 Mbit Ethernet is so high that up to 5 devices can be addressed simultaneously via a single line.

Investment protection for fieldbus devices

Hilscher also observes the Ethernet trend in the sales figures of its products. Demand has increased noticeably in the last two years. But with a market share in excess of 70%, the fieldbus technology is still strong and will continue for years to come. "Thus the duty of the mechanical engineer to support both systems for a long time becomes a pleasure for us," explains Beck. In the concept phase of the new product, therefore, the focus was on investment protection. "The goal was not just to replace fieldbus with Ethernet, but to let both technologies merge together in the simplest possible way." Thus, proven fieldbus devices can continue to be used and a broad market can be addressed. "This was the idea behind a TCP / IP-based gateways. "There are already some TCP / IP gateways in the market, but these devices only convert pure I / O data," says the gateway specialist. "Our Nethost supplements the service offering here with acyclic services, diagnostic and status messages and thus completely integrates the lower-level system."

For example, the mode of operation as a class 2 Profibus master, the sending of DPV1 read / write services or the pure CAN telegram transmission are supported in addition to the actual protocol handling as CAN open master. TCP / IP ensures data transfer to and from the Nethost. The telegrams transmitted in this case are coded and classified according to type and purpose in a few bytes at the beginning of the telegram. The coding logic is available in C source code. It maps to a socket interface and can therefore handle any TCP / IP stack without problems.

On the application side, it abstracts from a simple procedural API function interface. Catchy functions such as Open, Close, Reset, Send, Receive or IO Exchange guarantee a quick understanding and thus short integration times. In the device, the functions are decoded and executed remotely. This is the basis RPC principle (Remote Procedure Call), A DLL enables the immediate use of a Nethost under Windows. A C toolkit shows a sample implementation under Linux to make it easy for embedded programmers to get started.

Remote access via remote PC card

"The accessibility features for a Nethost are in keeping with the manufacturer's platform strategy. Once integrated - everything works' identically to the PC cards," says the product manager. Simply exchanging the PC cards for the Nethost DLL under Windows allows, for example, exchanging both product series without having to change the user program. What was controlled locally yesterday, can be controlled tomorrow via Ethernet via the control level from a distance.

"The same API makes Nethost a remote desktop PC card. In systems without a slot for PC cards, the device is even a direct replacement for PCMCIA cards, "Beck comments on access via Ethernet. Crucially, "If a system already supports our PC cards, it now also supports the operation of a Nethost." For example, IBH Softec was one of the first companies to integrate the functionally identical DLL into its Step-7-compatible Soft-PLC, Soft-PLC S7-315 / Soft-PLC S7-416 and now supports not only CIFX PC cards but also the Profibus Nethost.

In addition, the automation company was able to directly acquire two additional existing customers for the integration of the Nethost, which has been purchasing large numbers of PC fieldbus cards for peripheral control for many years. According to their own statements, both of them are working on a new control generation after 15 years of use. Due to their compactness and higher flexibility, they can only communicate via standard Ethernet interfaces. Nevertheless, they do not want to give up the support of established fieldbus technology and offer a migration path from the old to the new generation. TCP / IPStack, standard Ethernet controllers and the programming experience with the PC cards ensure short integration times. Today, it is therefore able to serve both the fieldbus customers and the Ethernet new customers alike, despite the switch to Ethernet.

TCP / IP conversion soon also for real-time Ethernet

The next step in Nethost development has already begun. Hilscher will launch three new variants in the third quarter of the year. The existing variants for Profibus, CAN open and Devicenet are supplemented by Profinet, Ethercat and Ethernet / IP masters. This takes into account the strong demand for TCP / IP implementation in the real-time Ethernet world. All variants are configured via a cross-device, uniform FDT / DTM-based configuration tool. If an engineering tool of the target system already exists, the alternative and open configuration via XML files ensures transparency. XML schemas put the configuration data in the correct format and can then be loaded into the Nethost after conversion to a binary file. Thus, the device can be fully integrated into each target system.
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