Modbus is the one of the world’s most popular protocols for communication between industrial devices. Originally designed for serial interfaces, Modbus has been successfully adapted to Ethernet technology and continues to play a major role in ever more advanced systems and architectures. However, it is important that Modbus integrators be familiar with certain issues that arise as legacy systems are upgraded or integrated into modern networks. In particular, determining the appropriate response timeout setting is a surprisingly difficult task that is often misunderstood or overlooked.

According to the Modbus protocol, all devices are classified as either a master or a slave. Masters initiate all communication and communicate only by sending requests to slaves. Slaves are passive and respond only to a master’s request. Every request that a master sends to a slave must be accompanied by a response from the slave back to the master, except in the case of broadcast requests. Masters can send a broadcast request to all slaves, in which case each slave simply obeys and no response is given.

The original Modbus protocol was not designed for simultaneous requests or simultaneous masters, so only one request on the network can be handled at a time. When a master sends a request to a slave, no other communication may be initiated until after the slave responds. The Modbus protocol specifies that masters use a response timeout function to identify when a slave is nonresponsive due to device or line failure. This function allows a master to give up on a request if no response is received within a certain amount of time. To allow for a wide range of devices, baudrates, and line conditions, actual response timeout values are left open for manufacturers to determine.

By not specifying a standard for the response timeout, the Modbus protocol can accommodate a wide range of devices and systems. However, the absence of timeout standards introduces additional challenges for system integrators working with legacy or proprietary devices.

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Determining the optimal response timeout value is essential to a system’s operational efficiency. If the timeout is set too low, a master may give up on a request too quickly, not giving the slave enough time to respond. With repeated failure to complete requests, the system becomes unusable. The slave may respond after the master has already initiated another request, causing unforeseen problems. Likewise, if the timeout value is set too high, valuable system resources are wasted if a master ends up waiting for a disconnected or malfunctioning slave to respond. With the inherent problem of network traffic and lag, it is even more critical to set effective timeout values so Modbus serial devices can interact properly with Ethernet devices.

Each slave device requires a different amount of time to process a master’s request, depending on how the device is designed. For example, a simple RTU may provide an immediate response if it simply needs to report the current reading of an attached sensor. However, a more sophisticated RTU may take longer to respond if several elements must be coordinated or if the data requires additional manipulation. For this reason, a device’s recommended response time is usually provided by the manufacturer, based on processing requirements and speeds. In order to determine a master’s appropriate timeout setting, system integrators take the recommended response times of each slave and apply further calculations based on baudrates and application requirements. With up to 31 slaves on a single serial line, finding the correct timeout setting for the master device can be a painstaking, laborious process.

Integrators face additional complications when dealing with devices that have a proprietary design. When a device is designed for a closed system, the manufacturers may have the optimal timeout settings already hard coded into the device. In this case, the recommended timeout values may not be provided, leaving integrators with no way to calculate the timeout value if the system needs to be maintained, expanded, or upgraded.

Even for systems that are not based on proprietary designs, integrators run into problems due to poor or unavailable technical documentation. As aging Modbus networks are upgraded, recommended timeout settings may be difficult to find due to documentation that was discarded or filed in a long-forgotten place. A time-consuming search through different archives may be required to locate the documentation or determine whether it even exists. Even if the documentation is found, it may be equally or more difficult to sift through the material for the recommended timeout value.

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The response timeout is often neglected when integrators troubleshoot problems with a Modbus installation, and many integrators may not even know what the response timeout is. Instead, the system’s baudrate may be lowered or other adjustments made until the system is finally operational. However, making this kind of compromise, which can lead to a degradation of system performance, could be avoided if the response timeout was set correctly.

If an integrator does not have the documentation required to determine the optimal response timeout setting, systematic trial and error must be used. With experience, Modbus integrators can often rely on intelligent estimates that are based on commonly used settings and an understanding of the likely cause of timeout errors. However, repeated testing and adjustment is still required to find the optimal value.

An alternative approach to response timeout values has been proposed as a feature in Modbus gateways, which connect Modbus TCP networks to Modbus RTU/ASCII networks. In a typical application, the Modbus gateway sits between the two networks and allows TCP masters to send requests to RTU slaves. Instead of requiring integrators to figure out the response timeout value, the gateway would automatically track response times as it forwards requests from TCP masters to RTU slaves, and dynamically update its own response timeout setting as it receives responses from RTU slaves. While this approach is easier for the integrator since the timeout value is automatically set by the Modbus gateway, there are some drawbacks. Since response times are only tracked for requests that are received, some slaves may not be represented in the calculation of the response timeout value. In addition, a slave’s response time can fluctuate wildly depending on the nature of the request sent, so the timeout setting may be too optimistic. Furthermore, every time the Modbus gateway is powered up, it would initially have no data to set the response timeout value and would need to start tracking response times all over again.

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Until now, the task of determining the appropriate response timeout value for a Modbus system has been frustratingly difficult. Modbus experts essentially had three choices for figuring out the timeout value:

However, a brand-new line of Modbus gateways now offers a new and effective solution.

This new approach tracks all response times at once, and uses a proprietary formula developed by MOXA's R&D engineers (patent pending) to derive the recommended response timeout value. The integrator simply clicks a button, and the Modbus gateway sends a universally recognized Modbus command to every single slave device in the system. Each slave’s response time is tracked, and the Modbus gateway’s response timeout value is then configured according to a carefully tuned formula. Although this method requires some time to complete, it only needs to be completed during initial installation or if a new slave device is added to the system. The gateway retains the setting when it is powered off and does not need to track response times again after being turned back on. More importantly, this new approach makes it easy for integrators to find the perfect response timeout setting for any Modbus system, saving a great deal of time and grief.

The response timeout setting has been a deceptively difficult issue for Modbus integrators. Without realizing it, many integrators may have allowed improper timeout settings to hurt system performance. Figuring out the right value to use has traditionally been a difficult and time-consuming process, even when the necessary documentation is readily available. However, with greater understanding and the development of a promising new approach, integrators may finally be able to handle this issue more effectively.

NOTE: MOXA's new line of Modbus gateways will be available starting at the beginning of April. Please contact a MOXA sales representative for more information about these products.

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The MOXA VPort 351, an industrial video encoder with Full Motion and Dual Codecs, will be ready for sale at the beginning of April. The VPort 351 is a high performance, 1-channel industrial video encoder that provides up to full D1 (NTSC: 720 x 480; PAL: 720 x 576) resolution @ 30 FPS and supports a dual MJPEG4/MJPEG algorithm, making it especially well suited for use with distributed surveillance systems in critical industrial applications. The VPort 351 can help you move your video over IP surveillance system into the industrial world!

The VPort 351 features DIN-Rail mounting capability, 12/24 VDC or 24 VAC redundant power inputs, and IP30 protection to meet the requirements of industrial environments. An extended temperature model with operating temperature range of -40 to 75°C is also available for outdoor and harsh environments such as roadways, refineries, and power plants. In addition, the VPort 351 has received important industrial and safety approvals, such as UL508, Class1, Div. 2, making it suitable for transportation, utility, and manufacturing systems. The VPort 351 has enclosure, EMI, and surge protection to protect against harmful interference.

VPort 351 Key Features

Ordering Information

Detailed product information is available on MOXA's global website at http://www.moxa.com/product/VPort_351.htm.

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ioLogik E2000 Active Ethernet I/O servers are now compatible with NI LabVIEW 8.

Active Ethernet I/O is a powerful new concept in remote data acquisition where I/O events trigger customized messages that are instantly sent to host computers. Active Ethernet I/O supports traditional Modbus/TCP for maximum compatibility with existing applications.

"NI LabVIEW is very popular in the fields of monitoring, testing, and measurement," said Andy Cheng, Division Manager of Active Ethernet I/O products. "Active Ethernet I/O is an opportunity to extend LabVIEW's remote monitoring capability." LabVIEW's built-in Modbus library can easily be used to connect to an Active Ethernet I/O server. LabVIEW also has a passive TCP software component that can instantly receive TCP/UDP messages from Active Ethernet I/O servers, without incurring any additional costs.

The application guide for using ioLogik E2000 I/O servers with LabVIEW is now available for download on MOXA's web site. For more information, please refer to http://www.moxa.com/Zones/Active_Ethernet_IO/index.htm

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The new TCF-142 V3.1 serial-to-fiber converter offers even greater transmission distances than V3.0 models. The converter comes in different models to transform serial signals into single-mode or multi-mode fiber, with each model equipped to handle RS-232 or RS-422/485 serial interfaces. For multi-mode models, fiber optic transmission distance has been improved to 5 km (originally 2 km), and for single-mode models, transmission distance is now 40 km (originally 20 km). On the new models, the power budget has been effectively doubled to provide higher data transmission distance and stability. Also, special models are available by request with different fiber optic connectors, such as SC/FC type connectors, or an even higher power budget (40 dB /80 km).

Click here for product details and ordering information.

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MOXA has experienced tremendous success with the TCC-80I, the world's first isolated high-speed port-powered converter, and the TCF-90/M/S, our high-performance port-powered serial-to-fiber optic converter. As a result, the warranty period for all serial port-powered products will be extended from 2 years to 5 years, which is the most generous warranty offered in the industry. This new warranty period applies to the entire family of serial port-powered converters, including the TCC-80, TCC-80I, TCC-80, TCF-90-M, and TCF-90S. Whereas other manufacturers are still providing only a 1-year warranty or none at all, MOXA is the only manufacturer providing a 5-year warranty on all serial converters.

Quality and confidence allows us to provide better service for our customers. This is why the new warranty period applies not only to new purchases, but also to current users of our products. Now, both current and new users can enjoy even greater benefits when using MOXA serial port-powered converters.

Click here for product details and ordering information.

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As the volume of air traffic grows, airports continue to expand their hardware and software to serve more customers. One of the most important systems is the radio system, which supports airport operations such as fleet, freight, logistics, and emergency management. Whether it is between the tower and the runways, or between the hangar and the terminals, voice communication at an airport usually involves a radio microphone.

The amount of territory occupied by airports has also grown, and as a result, buildings, terminals and other operational offices can be more than 25 km away from each other. Airport radio control systems must be upgraded to handle the increased distances between controllers, but it is challenging and expensive.

Typically, this problem is addressed by using media converters and fiber optic cables to extend transmission of the RS-422 serial signals.

A simple and cost-effective approach involves using MOXA's TCF-142 converters arranged in a fiber optic network. In the MOXA solution, most of the controllers are connected by pairs of TCF-142-S V3.1 converters, each of which extends RS-422 signals up to 40 km, which is farther than any other converter. In addition, the TCF-142-S-T V3.1 can operate in extreme temperatures from -40 to 75°C, making it ideal for use in exposed outdoor cabinets.

By using this approach, the cost to upgrade and maintain the radio control system is immediately and dramatically reduced. The fiber optic communication allows data to travel over longer distances, and also provides EMI protection. In addition, installation is much easier since no configuration is required. As opposed to the 20 km supported by other converters, MOXA's TCF-142-S V3.1 can transmit over a distance of 40 km. These advantages make the TCF-142-S V3.1 the perfect solution for extending communication between radio controllers over long distances.

Advantages of TCF-142 converters:

For more information, please contact your MOXA sales representative.

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Digital CCTV is a common component of reliable SCADA systems. However, it requires the attachment of many encoders and decoders to the system, and data must be transmitted according to the IEC 60870-5-104 protocol. It is difficult and often expensive to establish an efficient management tool to control camera parameters such as sequence, positions, and text.

A company in Europe decided to use MOXA's UC-7110 embedded computer to construct a reliable SCADA system. With two RS-232/422/485 serial ports and two LAN ports, the UC-7110 was able to connect many devices such as controllers, encoders, and decoders to the SCADA system. The UC-7110 offers stable communication with reliable data flow control, and it reduces the effort required to duplicate remote devices. Furthermore, the flexibility and power provided by the UC-7110 is helpful in reducing cable complexity, simplifying system architecture, enhancing functionality, and controlling data flow. With the well-designed software tools that are provided, programmers can turn the UC-7110 into a customized solution by developing software for protocol conversion and data transmission.

Using the UC-7110 in this SCADA application brings the following benefits:

Click here for more information on UC-7110 embedded computers.

Click here for more information on MOXA embedded computers

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Developing countries rely heavily on the building construction industry, and the availability of concrete can be a critical factor in a nation's development. To achieve more efficient concrete production, companies have increasingly relied on automated systems. An excellent solution involves using MOXA's I/O servers as part of a smart concrete production plant, and different product lines are specially designed for different systems. The ioLogik 4000 series is designed for high density environments, whereas the ioLogik 2000 line is ideal for distributed environments. Whichever ioLogik server is used, the powerful DLL library provided by MOXA makes it easier for programmers to develop robust applications for their specific needs.

Architecture Requirements

Why Moxa?

Introduction
One of the world's leading machine builders specializes in providing complete production lines for filling, labeling, and packaging. As an innovator in Ethernet-controlled machine automation, this company is leading a paradigm shift in machine control where an industrial network is essentially grafted onto a single machine or set of machines. By relying on Ethernet, the builder's line-up of integrated machine solutions can enjoy many advantages in areas such as stretch blow-molding technology, filling and closing technology, labeling and dressing technology, inspection and monitoring technology, process engineering, brewing technology, and much more. One of their flagship solutions is a complete soft drink bottling production line that comprises three primary machines—a filling machine, a labeling machine, and a packaging machine. The company needed several best-in-class, industrial-grade Ethernet switches that would be used for the internal network in this and other integrated machine solutions.

System Description
Each machine combines PLC controllers, an HMI control panel, and numerous I/Os, relays, sensors, and counters, all of which are Ethernet-based. The machine builder needed a proven, reliable Ethernet switch to form the internal communication network between these devices at the system (machine) level. The network also needed to port out to the factory floor to integrate with other process machinery and allow remote monitoring and control. Since the company designs and builds machinery for the food packaging industry, sanitation and maintenance requirements are also critical factors in system design. Machinery must be built to withstand high-pressure, high-temperature washings, as well as the cleaning solvents used for sterilization.

The builder selected MOXA's EDS-305-M-SC, EDS-308-M-SC, and EDS-316-M-SC unmanaged Ethernet switches. These rugged Ethernet switches are specially designed to withstand the range of temperatures, vibration, and electrical noise typical of industrial environments. Each of these models includes one multi-mode fiber optic port capable of transmitting data up to 5 kilometers to provide reliable, high-speed data transfer between machines or to the central control room. Redundant DC power inputs and an operating temperature range of 0 to 60°C are standard, and special models are available that can operate between -40 and 75°C. Each switch also has a 5-year warranty and comes with relay contacts that activate an alarm when the power fails or a port link breaks. By using watertight sensors and enclosed EDS Ethernet switches, the builder was able to design solutions that meet the demanding system requirements.

Benefits of EDS-305-M-SC, EDS-308-M-SC, and EDS-316-M-SC:

Background
Wireless service providers rely on network optimization and evaluation systems, many of which are installed in vehicles for mobility, to ensure reliable, uninterrupted service. Frequent onsite maintenance by a technician is required for maximum effectiveness. However, many pieces of equipment must be managed using a serial console, and lugging a PC between sites is not feasible.

Solution
To keep technicians mobile, a laptop is used instead of a PC for serial console connections. Since laptops typically come with USB ports instead of COM ports, a USB-to-serial hub is a critical accessory.

MOXA's UPort 1410 is a USB-to-serial hub that adds four RS-232 ports through one USB port. The hub is the size of a paperback novel, giving the laptop maximum mobility and functionality. With UPort installed, technicians can be both mobile and well-equipped to perform tests such as handset quality, dial, MOS, C/I, scanner CW, pilot scanning, spectrum, and UMTS video call tests.

Benefits

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MOXA is pleased to announce the launch of the Embedded Applications Site, which explores how our embedded computer products are used in different vertical markets.

Many software partners have already developed applications for our ready-to-run embedded computers, which provide reliable operation over wide temperature ranges. The new website presents the different ways that our products are used in embedded applications. System integrators and software partners now have an excellent tool to introduce our embedded computers and solutions to various vertical markets, such as power, transportation, POS, environmental monitoring, manufacturing automation, and medicine.

Our embedded solutions are designed for industrial applications and are easy to implement with different operating systems. They offer a user-friendly environment for both Linux and Windows CE programmers, and allow software partners to develop applications with ease.

The Embedded Applications Site is located at the following URL:

http://www.moxa.com/Zones/Embedded_Computing/
Embedded_Applications/index.htm

If you have any comments or suggestions, please contact us at info.sys@moxa.com.

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MOXA is pleased to announce our participation at the 2007 Hannover Messe tradeshow in Hannover, Germany, from April 16 to 20, 2007. Three key themes will be the focus of the MOXA exhibit: gigabit solutions, wireless solutions, and Active Ethernet I/O solutions. Our full line of products will also be displayed, including Active Ethernet I/O servers, industrial Ethernet switches, serial device servers, embedded computers, GPRS modem/routers, USB to serial hubs, and industrial video servers. Everyone is encouraged to come to the 2007 Hannover Messe and visit us at the MOXA at Booth. Staff will be on hand and happy to answer your questions.

MOXA will also be presented at the Modbus-IDA booth at Hall 9, Stand A59. The Modbus-IDA exhibit will focus on Modbus applications that rely on wireless connections. One of their featured products will be MOXA MGate MB3000 Modbus gateway, which makes it easy to integrate Modbus serial with Modbus Ethernet. The MGate MB3000 features automatic calibration of response timeouts and smart routing of TCP requests to serial slaves. It is designed to integrate Modbus networks seamlessly, without altering existing system architectures.

Hannover Messe is renowned as one of the world leading showcases for industrial technology, and provides an excellent opportunity to learn about MOXA newest product offerings and the latest developments in industrial communication technology.

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