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FAQ – Questions and Answers about AS-Interface

Here you can find an overview of frequently asked questions about our products and devices as well as about AS-Interface, ASi-5 and IO-Link.


Are you unable to find the answer to your question? No problem, of course we will gladly answer your individual questions via phone or e-mail. If you have any technical questions, our technical support team will be happy to assist you.

Questions about our products

The "Bihl+Wiedemann's Choice" range consists exclusively of best-practice products that combine the highest level of user experience, are nearly always in stock in large quantities and can usually be shipped right away. "Bihl+Wiedemann's Choice" items are suitable for almost all standard applications and are also very attractively priced thanks to the quantities produced. We have introduced the "Bihl+Wiedemann's Choice" labeling to provide our customers with a quick decision-making aid while clearly highlighting what advantages the respective product has for the customer.


We provide corresponding device description files (GSD files) for all Bihl+Wiedemann gateways. These are available as a ZIP file in the "Downloads" tab on the product detail pages of the devices.


Please register or log in to download the file.

We provide corresponding device description files for all Bihl+Wiedemann gateways. The EDS files for EtherNet/IP gateways are available as a ZIP file in the "Downloads" tab on the product detail pages of the devices.


To the EtherNet/IP gateways


Please register or log in to download the file.

Here you can download the current parameter library for calculation tools (SISTEMA and others) as a ZIP file: 


Parameter library


Please register or log in to download the files.

We provide EPLAN macros for most of our products. These can be found as a ZIP file on the product detail pages within the "Downloads" tab under the "EPLAN Macros" sub-item.


Please register or log in to download the files.

We provide various manuals to help you commission and use our devices. Guides and manuals can be found on the product detail pages within the "Downloads" tab. For every item, we provide various documents as PDF and sometimes also as a video tutorial, including:


  • Compact handbooks
  • Operating instructions
  • Assembly instructions
  • Software manuals
  • Display menus (for gateways)
  • Application examples
  • Example programs
  • Quick start guides
  • Video tutorials


Please register or log in to download the files. Some of the files are only visible after logging in.

We provide a wide range of safety I/O modules for the connection of OSSDs (optoelectronic protective devices), floating contacts, and antivalent switches in IP20 and IP67 versions. You can find an overview of corresponding products here:


To the safety I/O modulesn


We are happy to provide you tailor-made solutions and special variants for your sensors on request.


Tel.: +49 621 33996-0
E-Mail: mailbihl-wiedemann.de

We recommend using the Bihl+Wiedemann Software Suite with integrated hardware catalog to set up your ASi circuits. If you have questions or encounter problems with the command interface, please contact our support team.


Tel.: +49 621 33996-0
E-Mail: asiexpertbihl-wiedemann.de

The earth fault monitor checks the symmetry of the ASi voltage. If the ASi voltage is no longer symmetrical, it means that there is limited immunity to interference during data transfer.


Earth fault checklist

Here you can find an "Earth Fault Checklist " in PDF format:


Earth fault checklist


Please register or log in to download the files.


If you encounter problems or uncertainties in handling this message, please contact our support team. Our product specialists will be happy to assist you.


Tel.: +49 621 33996-0
E-Mail: asiexpertbihl-wiedemann.de

Please contact our support team. Our product specialists will be happy to assist you.


Tel.: +49 621 33996-0
E-Mail: asiexpertbihl-wiedemann.de

Yes, a perceived high temperature is normal and completely safe. The housings are made of stainless steel and unlike plastic housings, they have good thermal conductivity. Therefore, they serve as heat sinks for the electronics.

The replacement device must have the same part number. You can then replace the defective node  without using a hand-held addressing device or additional programming work. The additional steps necessary depend on the slave type used (e.g. standard or safety). You can find more information in our video tutorial.


If you encounter problems or issues related to this topic, please contact our support team. Our product specialists will be happy to assist you.


Tel.: +49 621 33996-0
E-Mail: mailbihl-wiedemann.de

The replacement device must have the same part number. You can then replace the defective master without additional programming work. Please attach to the following necessary steps:


  1. Disconnect the defective safety monitor from the power supply and from the ASi network.
  2. Remove the chip card from the top of the defective unit and insert it into the replacement unit.
  3. Connect the new monitor to the ASi network and the power supply.
  4. The display menu of the monitor willguide you through the copying process to help you transfer the stored configuration from the chip card to the device.
  5. You may be asked to specify the direction in which the copying process is to be started – in this case, select "Chipcard > Master".
  6. Enter the release code of the configuration and confirm this code. The safety monitor then starts and the transfer is completed.

The above steps are described in detail in our video tutorial.


If you encounter problems, please contact our support team. Our product specialists will be happy to assist you.


Tel.: +49 621 33996-0
E-Mail: mailbihl-wiedemann.de

Questions about the ASi Cable

The cable used for AS-Interface is an unshielded, non-twisted, two-wire yellow flat cable that can be connected with reverse polarity protection. It serves simultaneously for the transmission of ASi communication and to supply power to field devices with low power requirements. A separate black flat cable is used to supply 24 VDC to customers with a higher power requirements, such as motors or valve terminals.

The sensors or actuators are usually connected via piercing technology. In this process, the insulation of the flat cable, which is profiled to protect against reverse polarity, is pierced during installation by means of two piercing pins, without the cable having to be prepared beforehand. In this way, slaves can be relocated or added directly to the cable at any time without major installation effort.

An ASi wire stripper is used for stripping ASi cables with an outer insulation of thermoplastic elastomer (TPE) or polyurethane (PUR).

ASi end caps are used to protect the bare ends of the ASi or AUX profile cable against dust and humidity up to max. IP67 – for interference-free communication in the ASi circuit. They are available as left and right versions.


Many Bihl+Wiedemann slaves and active distributors do not generally require the use of end caps because the cable ends can be terminated in the base.

The total length of the ASi standard network is limited to 200 m for ASi-5 and 100 m for ASi-3. When determining the total length, all junctions must be included in the calculation. For example, with a combination of ASi repeaters and bus terminations, the maximum achievable distance between two slaves in an ASi-3 network is 1,000 m, if the master is appropriately positioned. No more than 2 repeaters (max. 2 connected in series) may be set between a slave and the master.


This is how you extend the ASi cable

The ASi cable is specified in the ASi standard (IEC 62026-2 or DIN EN 62026-2).

The ASi profile cables BW1979 and BW1980 are suitable for drag chains. The installation instructions of the cable manufacturers must be observed, e.g., no upright installation in the drag chain.

Questions about ASi-5

No. ASi-5 is the evolution of the well-proven AS-Interface standard. ASi-5 offers all the advantages that have already made ASi so special in the past. For example, power and data are still transmitted over a single cable, you have free choice of your topology and the safety technology is still on the same infrastructure. The main reason for evolving ASi was the fact that Industry 4.0 and increasing digitalization brings with it ever greater volumes of data. ASi-5 has both a large data size and short cycle times, making it possible to transport more and more data, without restrictions, to where they can yield valuable information.

Yes. ASi-5 is compatible with all earlier ASi devices and components, meaning that ASi-5 nodes  can be combined with ASi nodes of any generation—in existing as well as in new ASi networks. In an existing ASi network, you can simply connect additional new ASi-5 slaves and easily continue to use existing ASi nodess. To use ASi-5 nodes all you need is a new Bihl+Wiedemann ASi-5 / ASi-3 gateway.

ASi-3 directly follows ASi-5. “Skipping” ASi-4 illustrates that this development step is really big. In addition, we did not want to suggest that Industry 4.0 is the sole innovation driver for the new ASi generation.

In particular for applications with high transmission speeds or high data volumes. In addition, in places where a concentrated and cost-efficient collection of a larger number of inputs and outputs is needed. In many cases, Bihl+Wiedemann’s new digital ASi-5 modules can be an affordable alternative to other fieldbus solutions.

Yes. AS-Interface remains a standard ensuring compatibility with components from any manufacturer. All certified products with an ASi logo can interoperate in a common network.

No. In principle, they can be configured without software but we always recommend the more comfortable option using our software solutions. Our software Suite enables you to easily plan, configure and parameterize ASi networks with or without safety. If you already use the software for your ASi network, all you need is a free update to be able to continue using it for ASi-5 applications. The software is as intuitive and comfortable to use as with ASi-3. An integrated hardware catalogue encompasses the complete ASi product range. All you need to do is click the device you need when configuring the ASi circuit. The new online bus information also enables you to easily address slaves and monitor inputs and outputs. This function makes it even easier to integrate IO-Link sensors.

Like all ASi generations, ASi-5 is a joint development of several manufacturers of AS-Interface products. The complete project took more than 200,000 developer hours, evolving the idea of a new ASi generation into a mature trendsetting technology. Now that the main project has been completed, the involved companies continue to work on standards and certifications for new ASi-5 products.

By combining ASi-5 and ASi-3 slaves on one ASi circuit, it is possible to connect at least 62 nodes – in many cases, even considerably more.


The Bihl+Wiedemann hardware catalog tells you how many ASi nodes can be connected for specific applications. It is integrated in our ASIMON360 and ASi Control Tools360 software. So a warning appears if the maximum possible number of ASi-5 and ASi-3 slaves is exceeded. In addition, vacant ASi-5 transport channels can be shown at any time when planning.


Our experts will gladly answer any further questions you may have.

Questions about IO-Link

The open IO-Link interface requires only a simple standard industrial cable. Intelligent sensors and actuators can be connected in a cost-efficient manner on an unshielded three- or five-wire cable. For point-to-point communication, each IO-Link device needs an IO-Link master.

The IO-Link master handles the communication to the intelligent sensors and actuators. It enables parameterization, diagnostics and access to the cyclic data by means of a connection to the control system.

Reduced machine-related costs

A cost-efficient standard cable establishes a connection up to 20 meters long between the IO-Link master and IO-Link device.


High machine availability

Downtimes are reduced because when a defective IO-Link device is replaced, its parameters are automatically transferred to the new sensor by the IO-Link master or control system.


Efficient operation

IO-Link devices can be positioned in the machine directly at the work site. These do not have to be accessible for parameterization.


Demand-oriented maintenance

Continuous diagnostic data of the entire process lengthen maintenance intervals, since systems and machines need to be maintained much less frequently due to the automatic readjustment via IO-Link


More information about the advantages of IO-Link

No. IO-Link is a point-to-point connection between an IO-Link master and an IO-Link device (sensor or actuator). The connection's cable length can be up to 20 meters.

IO-Link is mainly used in industrial production automation for communication with sensors and actuators.

It is possible to extend existing bus systems. As a prerequisite, the system mapping of IO-Link for the respective bus system must be already implemented. It is particularly easy to use IO-Link in conjunction with the ASi intelligent wiring system. Thanks to piercing technology, corresponding IO-Link masters can be easily retrofitted where they are needed.

Questions about Passive Safety

Without passive safety, one cannot assume that safe switch-off/disconnection of AUX on a standard I/O module will result in a safe state (I/Os de-energized), as this is not guaranteed. The module continues to draw energy via AS-i, and in the event of a fault, the energy might be fed back via AS-i into the AUX network, which is safely switched off.


Thus, the safety achieved by the safe switch-off cannot be guaranteed in the event of a fault. Furthermore, it can lead to unplanned downtimes and increased effort in system planning, installation and commissioning.

Safe switch-off (passive safety) is standardized by the Machinery Directives 2006/42/EC, EN ISO 13849-1 and EN 62061.

Passive safety is applicable when the safe state of the machine's plant components, which are to be provided with passive safety, can be achieved by de-energizing them (active current principle).

All components that have a connection to different supply potentials and are in the path of a machine's safe switch-off must be passively safe.

Unfortunately, in order to use such products to add passive safety in a machine that was not previously safeguarded by passive safety, it is not enough to just replace the modules. In this case, a new safety assessment must be carried out on the machine.

This information can be found in our data sheets under the "Environment" category.

Questions about the new 30 V Power Supplies

Since ASi transmits power and data simultaneously via the yellow cable, the DC power supply must be decoupled from the AC communication. In the past, this was implemented in a special ASi power supply. Bihl+Wiedemann has integrated this data decoupling in all current gateways, so that all devices can now be operated with ordinary 24 V power supplies. However, there are limitations related to maximum cable length and performance. To ensure efficient supply to the participants, as well as use of the full cable length, we recommend our new range of power supplies. This is also optimized for ASi-3 and ASi-5 communication.

Because we have optimized all new power supplies in endurance tests for use with our ASi-5/ASi-3 Gateways. Interference, which is common in power supplies, is reduced to a minimum in areas relevant to ASi-5.


Yes, the previous power supplies – whether 30 V* or ASi – are still available. If a faulty device needs to be replaced, it is recommended to use a replacement device that has the same item number. When designing a new system or refurbishing an existing machine, it is recommended to use the new 30 V power supplies in combination with ASi-5/ASi-3 Gateways.


* With the exception of BW1927, we are happy to offer model BW4220 as an alternative.

Yes, the new power supplies also work very well with classic ASi-3 Gateways. However, only under one condition: in the technical data of the gateway, there must be a "Yes" for the criterion "1 Power Supply, 1 GW for 2 ASi circuits" (see, e.g. BWU2546). For all other ASi-3 Gateways and ASi-3 repeaters the ASi power supplies are of course still available.

If FE is connected to the ASi-5/ASi-3 Gateway (functional earth) of the system earthing, there is +15 V between ASi+ and the system earthing and -15 V between ASi- and system earthing. The new power supplies output a differential voltage of 30 VDC. The balancing with respect to FE – together with the decoupling of the communication from the power supply – is realized in the ASi-5/ASi-3 Gateway.

Yes, the new 30-V power supplies each provide a maximum output current that can be distributed between multiple gateways with decoupling. For example, a possible combination is the operation of two ASi Gateways with two circuits, each with 4 A decoupling in parallel and a 16 A power supply.

Questions about the ASi-5/ASi-3 Addressing Device

Yes, because you can easily address ASi modules of all generations using the ASi-5/ASi-3 addressing device. You will also profit from its modern product features: an OLED color display, a powerful energy storage device (supercapacitor) and simple PC connection via a standard USB-C port.

Yes, we supply the respective ASi addressing cable as an accessory. Find out more about our wide range of ASi addressing cables here.

No, you can also commission all ASi modules using just the Bihl+Wiedemann software suite or directly at the gateway. However, the addressing device may simplify the commissioning of an ASi circuit. It enables you to quickly and easily assign an address to the bus nodes without the need for a real bus structure. Commissioning is then performed automatically by the software, if the ASi bus is connected to the PC software via a gateway.

Questions about 48 V Drive Solutions

To start with, there is the ASi-5 motor module for Interroll EC5000 AI (BWU4212) for efficient control of 48 V motors. Products from other manufacturers and drives can also be controlled with relevant ASi solutions from Bihl+Wiedemann on request. Integration is also possible in "Logistics 4.0" using the new ASi-5/ASi-3 gateways for fieldbuses such as PROFINET, EtherNet/IP, Sercos or EtherCAT.

Compared to other multi-zone controls for conveyor applications, the ASi-5 motor modules from Bihl+Wiedemann and the ASIMON360 configuration software significantly reduce the configuration effort. Settings and parameters are only assigned for the first motor module. These can then be easily copied to all additional modules. The entire system requires only one IP address and only one Web server — the Bihl+Wiedemann system can be put into operation quickly and easily.

ASIMON360 supports consistent, harmonized labeling and identification of equipment within drive systems from the electrical designer's eCAD system to PLC programming portals such as Siemens' TiA (Totally Integrated Automation). To do this, the electrical planner can download an EPLAN macro from the Bihl+Wiedemann website, add the desired devices and carry out the wiring for ASi, auxiliary power, I/O signals and parameters.

Questions about Single Pair Ethernet

Users have a choice: Shielded/unshielded options are available for each SPE standard. However, these cable variants are not necessarily mentioned in the specifications. Depending on the standard, which in turn determines the speed, the cable length can be significantly increased by using a shielded SPE cable. For example, from 15 m (unshielded) to 40 m (shielded) at 1 Gbit/s as defined by 1000BASE-T1 or IEEE 802.3bp.

The SPE System Alliance consortium makes the following statement on its homepage (singlepairethernet.com): "A complete 360° enclosed stainless steel sheath surrounding the entire connector [SPE] provides excellent electromagnetic compatibility (EMC)." It can therefore be assumed that SPE is EMC-resistant in the industrial environment, especially with the connector and cable shielding mentioned above. Due to the current stage of development, no further details are available.

SPE uses the so-called multidrop method, which does not exist in conventional Ethernet. This means that the reach is shorter with SPE, but also that only simple T-pieces without switches are required. Moreover, the cables and connectors are significantly smaller with SPE.

Since PROFINET is an Ethernet-based protocol, it can basically be transmitted via SPE. SPE is just a new physical layer, i.e., new hardware for the transfer of information from protocols such as Ethernet.


The different physical layers are connected via a switch to enable them to communicate with each other.

Due to the current stage of development, no precise details have been published to date. However, it can be assumed that the wiring in such an application scenario is based on the implementation using conventional Ethernet.


It would make sense to connect a switch with 32 ports, each with the data rate of 10 Mbit/s, to a control system via a 1 Gbit/s port. This is the only way to ensure that every port can use the full bandwidth at all times. Most SPE applications in the field could be a combination of switches and point-to-point connections. The point-to-point connections, each limited to 1,000 m in length, would connect the attached sensors to the switch

SPE and ASi-5 both offer a lean, lightweight, yet powerful infrastructure. As a result, they make Ethernet in the field superfluous in many aspects. At the same time, SPE and ASi-5 make it easier for the industry to digitize the field level – and thus take the step towards IIoT.

Our Technical Support can be reached at:

Phone: +49 621 33996-0

Fax: +49 621 3392239

E-Mail: supportbihl-wiedemann.de