Demystifying DeviceNetApril 2013 TechConnect Genius Webinar

Frequently Asked Questions

Demystifying DeviceNetApril 2013 TechConnect Genius WebinarFrequently Asked Questions

General Questions..................................................................................................................................................... 1So now that Bob has retired, Rod is going to continue publishing updates to the Book of Knowledge?.................1

If I need to reach nodes that are 50 feet away, is there such a thing as a "repeater" that will allow me to get the extra distance?........................................................................................................................................................ 1

Is there 6 Meters between nodes on a daisy chain drop, or 6 Meters to the furthest node in the series chain?.....1

Any reasons why we would use DeviceNet instead of Ethernet/IP?.......................................................................1

Is there a Tap used to break the V+ in the cable?...................................................................................................1

So can you have both COS and Cyclic on the same network?...............................................................................1

What if you have multiple failures at the same time? Does ADR still work?............................................................1

ADR: Are manufacturers required to maintain ADR functionality on newer product revs forever or until product code changes? The issue is how long will ADR hold? Months? Years? If you uncheck major and minor revs on ADR, is the ADR supposed to work as long as the product code doesn't change?................................................1

Do you recommend having Safety related switches like Pull Cords, Emergency Stops on DeviceNet?.................1

12 of my E3Plus nodes go to default values when power is removed from the PLC. How do I keep my programmed settings when I have to lockout power?.............................................................................................2

For a multi-network DeviceNet system, would there be any comparison/contrast to using 1788-EN2DN EtherNet/IP to DeviceNet Linking Devices vs. the 1756-DNB DeviceNet Bridge/Scanner Modules?.....................2

Will DeviceNet be around for a while or will it be replaced by Ethernet?.................................................................2

Can you clarify the distinction between polled and strobed devices?......................................................................2

I used a DeviceNet PV once(only once) can you get more than the 64 word limit with messaging now or are you still limited? I am just curious if you can get 20 floats in and out easily...................................................................2

Every vendor is providing Remote I/Os which can save cabling cost. The popularity of Ethernet is increasing and it has been accepted as reliable means of communication how do you see future of DeviceNet?.........................2

Can ADR set the baud of a device?........................................................................................................................ 2

What advice can you offer on choosing RPI for the DNB, supposing a rack that is mostly DI &DO - e.g., lightly loaded?................................................................................................................................................................... 2

Does DeviceNet have any advantages over Ethernet?...........................................................................................2

The 193-DCAT module is basically a scanner on EtherNet. I ran into a DeviceNet off situation w/ 3 193s on the same DeviceNet network at power up. Is there a way to have configured them to do their scanning w/o the lowest node chatter time out?................................................................................................................................. 2

What can happen if we put a node at the end of the trunk cable and include the termination resistor?..................2

Has there been a study of network media life expectancy (i.e., pin and sleeve wear on a connectorized network due to vibration or connector strain)?......................................................................................................................3

Trying to add explicit messaging to Power Flex 40 Drives on an old Device Net System using a PLC-5 with the old 1771 I/O and DSn Scanner. Is there a good source of help in the form of an instruction book you can recommend?........................................................................................................................................................... 3

How does ADR know what device is assigned to what node if there is multiple failures?.......................................3

How can I create the excel file?...............................................................................................................................3

If a device has input and output data but is mainly used as an input device, e.g., photo-eye, how do you set it up to be strobed?......................................................................................................................................................... 3

Do all PLC products that have DNET now have the scanlist backup to processor or scanner option?...................3

Is there any tool (meter?) or software means of diagnosing an operating DeviceNet to evaluate actual inter-scan delay or bandwidth usage? I see on some of my DeviceNets that messaging for DriveTools, etc. is sometimes very, very slow - wondering if my DeviceNet is too heavily loaded or if drive configuration data is just too large and unwieldy for a serial network............................................................................................................................3

General Questions

1. So now that Bob has retired, Rod is going to continue publishing updates to the Book of Knowledge?

Yes, Rod Shearer will be updating the DeviceNet Book of Knowledge which is available as Knowledgebase document 488833.

2. If I need to reach nodes that are 50 feet away, is there such a thing as a "repeater" that will allow me to get the extra distance?

This topic is covered in the DeviceNet Book of Knowledge which is available as Knowledgebase document 488833. There are several options described; 1734-ADNX as well as a few products from Encompass Partner WRC.

3. Is there 6 Meters between nodes on a daisy chain drop, or 6 Meters to the furthest node in the series chain?

The maximum drop line length from trunk line to the end node on a series chain drop is 6 meters. NOTE: Allowable current available on a 6 meter drop is 0.75 A. DNET-UM072 page 26 / 130.

4. Any reasons why we would use DeviceNet instead of Ethernet/IP?

All networks have their pros and cons. A Network Selection guide is available on the Rockwell Automation Literature Library publication NETS-SG001 that describes different network options including our core networks ControlNet, DeviceNet and Ethernet/IP as well as others.

5. Is there a Tap used to break the V+ in the cable?

A PowerTap may be used to segment network power supplies as described in the DeviceNet Book of Knowledge located in Knowledgebase document 488833.NOTE: Power Taps are only needed where power supplies are added to network outside of a sealed enclosure. Most power connections are made inside the main control cabinet using ordinary terminal strips.Additional information on DeviceNet PowerTap can be found in publication On-Machine Connectivity DeviceNet Media.

6. So can you have both COS and Cyclic on the same network?

Yes, all of the DeviceNet communication options can coexist on the same network. Strobed, Polled, Change of State (COS), Cyclic and Explicit Messaging. The key thing to remember is that only one device can communicate at any point in time. Who gets to communicate and when is managed with Prioritization and Arbitration.

7. What if you have multiple failures at the same time? Does ADR still work?

This question is addressed in Knowledgebase document 16582 ADR – Frequently Asked Questions. Question: What happens if one device fails and before I can change it, another fails?Answer:The scanner can handle any number of device failures simultaneously. However, the AAR feature will be disabled for devices that have the same Electronic Key.Question: What if two exact devices fail at the exact same time?Answer:If two devices fail that have the same Electronic Key, the scanner will disable the AAR feature, if enabled for only those devices. However, the CR feature will still be active. In this case, a software tool must be used to change the node's address. The Node Commissioning Tool that ships with RSNetWorx for DeviceNet can be used to change a node's address.

8. ADR: Are manufacturers required to maintain ADR functionality on newer product revs forever or until product code changes? The issue is how long will ADR hold? Months? Years? If you uncheck major and minor revs on ADR, is the ADR supposed to work as long as the product code doesn't change?

No, manufacturers are not required to maintain ADR functionality on newer product revisions. ADR will function without issue as long as the configuration information remains the same. Error 89 will be displayed for a device where an error has occurred during the ADR process such as the scenario where the electronic keying is relaxed to the point where the configuration changes although the electronic key matches. If you are concerned about this my suggestion is to specify Major Revision in addition to the default electronic keying which includes: Vendor, Device Type and Product Code. For Rockwell Automation products if a device’s configuration information were to change the product’s Major Revision would likely also change.

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9. Do you recommend having Safety related switches like Pull Cords, Emergency Stops on DeviceNet?

Safety products exist for DeviceNet and Ethernet/IP. All networks have their pros and cons. A Network Selection guide is available on the Rockwell Automation Literature Library publication NETS-SG001 that describes different network options including our core networks ControlNet, DeviceNet and Ethernet/IP as well as others.

10. 12 of my E3Plus nodes go to default values when power is removed from the PLC. How do I keep my programmed settings when I have to lockout power?

Please contact technical support to discuss the specifics of your application and the best way to address the program settings being lost in your E3+ modules when power is removed from the PLC.

11. For a multi-network DeviceNet system, would there be any comparison/contrast to using 1788-EN2DN EtherNet/IP to DeviceNet Linking Devices vs. the 1756-DNB DeviceNet Bridge/Scanner Modules?

A simple way to think of the 1788-EN2DN module is as a 1756-DNB module in an Ethernet connected chassis. As such, a 1756-DNB module in a local chassis with the processor has superior performance because the Ethernet/IP segment does not exist. Of course depending on how many networks you have the largest chassis size for a single ControlLogix processor is 17. A question you should ask yourself is how many DeviceNet networks do you want dependent on a single processor?You may wish to contact technical support or your local Rockwell Automation sales office to discuss this question as well as others in relation to the details of your application.

12. Will DeviceNet be around for a while or will it be replaced by Ethernet?

DeviceNet is one of the world's leading device-level networks for industrial automation. I expect that it will be around for a while. DeviceNet offers robust, efficient data handling because it is based on Producer/Consumer technology. This modern communications model offers key capabilities that allow the user to determine effectively what information is needed and when.

13. Can you clarify the distinction between polled and strobed devices?

This topic is covered in the DeviceNet Book of Knowledge which is available as Knowledgebase document 488833. Reference the Protocol Notes section.

14. I used a DeviceNet PV once (only once) can you get more than the 64 word limit with messaging now or are you still limited? I am just curious if you can get 20 floats in and out easily.

The DeviceNet PanelView is still limited to the 64 word limit and for your information the DeviceNet PanelView is no longer available for order. The suggested replacement is a PanelView Plus with Ethernet communications.

15. Every vendor is providing Remote I/O modules which can save cabling cost. The popularity of Ethernet is increasing and it has been accepted as reliable means of communication how do you see future of DeviceNet?

DeviceNet is one of the world's leading device-level networks for industrial automation. I expect that it will be around for a while. DeviceNet offers robust, efficient data handling because it is based on Producer/Consumer technology. This modern communications model offers key capabilities that allow the user to determine effectively what information is needed and when.

16. Can ADR set the baud of a device?

No, for ADR to function the scanner must be able to communicate with the device which would require that the device be at the same baud rate. This could be an issue if the device does not support Autobaud or allow a method of manually setting the baud rate AND the baud rate of the network is not the default of 125K.

17. What advice can you offer on choosing RPI for the DNB, supposing a rack that is mostly DI &DO - e.g., lightly loaded?

From what you have described the ControlLogix controller in this case should be able to handle a full sized 1756-DNB module at the fastest RPI = 2ms. The Logix 5000 Task Monitor Tool provides access to controller loading. The Logix 5000 Task Monitor Tool is an optional install with RSLogix5000 / Studio 5000.

18. Does DeviceNet have any advantages over Ethernet?

All networks have their pros and cons. A Network Selection guide is available on the Rockwell Automation Literature Library publication NETS-SG001 that describes different network options including our core networks ControlNet, DeviceNet and Ethernet/IP as well as others.

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19. The 193-DCAT module is basically a scanner on EtherNet. I ran into a DeviceNet off situation w/ 3 193s on the same DeviceNet network at power up. Is there a way to have configured them to do their scanning w/o the lowest node chatter time out?

193-DNENCAT(R) Ethernet/IP to DeviceNet linking devices do function as a scanner to a maximum of nodes on DeviceNet network and is referenced in the DeviceNet Book of Knowledge. It is slightly unclear what you are describing with ‘lowest node chatter time out’. If you are describing the situation that can occur with Change of State devices with data that changes frequently this can be addressed with the Inhibit time which is described in the 193-DNENCAT(R) User Manual publication 193-um014 in chapter 3. If this is not the case or you have further questions please contact Rockwell Automation Technical Support.

20. What can happen if we put a node at the end of the trunk cable and include the termination resistor at that node?

It is perfectly fine to install a termination resistor at the end node.

21. Has there been a study of network media life expectancy (i.e., pin and sleeve wear on a connectorized network due to vibration or connector strain)?

I expect that a study exists. My suggestion is to contact technical support and they can direct you to the correct resource to address your question on the specific cable(s) and connector(s) you have in mind.

22. Trying to add explicit messaging to Power Flex 40 Drives on an old Device Net System using a PLC-5 with the old 1771 I/O and DSN Scanner. Is there a good source of help in the form of an instruction book you can recommend?

This question is addressed in the 1771-SDN Installation Instruction manual publication 1771-in014. If you require further assistance contact Rockwell Automation Technical support.

23. Is there a way to view the actual bandwidth usage? (i.e., with the error frames included?)

To monitor actual bandwidth usage including error frames would require a product such as the Brad Harrison NetAlert .

24. How does ADR know what device is assigned to what node if there is multiple failures?

This question is addressed in Knowledgebase document 16582 ADR – Frequently Asked Questions. Question: What happens if one device fails and before I can change it, another fails?Answer:The scanner can handle any number of device failures simultaneously. However, the AAR feature will be disabled for devices that have the same Electronic Key.Question: What if two exact devices fail at the exact same time?Answer:If two devices fail that have the same Electronic Key, the scanner will disable the AAR feature, if enabled for only those devices. However, the CR feature will still be active. In this case, a software tool must be used to change the node's address. The Node Commissioning Tool that ships with RSNetWorx for DeviceNet can be used to change a node's address.

25. How can I create the excel file?

The excel file is available in Knowledgebase record 20862 DeviceNet Performance – Approximating Wire Time.

26. If a device has input and output data but is mainly used as an input device, e.g., photo-eye, how do you set it up to be strobed?

My suggestion is to reference device specific documentation for what connection options are supported. If a device has output data it cannot be mapped as strobed even if you are not interested in using the output data.

27. Do all PLC products that have DNET now have the scan list backup to processor or scanner option?

Knowledge base document 16582 ADR – Frequently Asked Questions provides a list of Rockwell Automation Scanners and minimum revision that support ADR.1747-SDN 4.0151771-SDN/c 6.0021756-DNB 3.0021784-CPCIDS 2.0081784-PCIDS 2.0071788-CN2DN 1.0201769-SDN/b 2.001

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1788-DNBO 1.001

28. Is there any tool (meter?) or software means of diagnosing an operating DeviceNet to evaluate actual inter-scan delay or bandwidth usage? I see on some of my DeviceNets that messaging for DriveTools, etc. is sometimes very, very slow - wondering if my DeviceNet is too heavily loaded or if drive configuration data is just too large and unwieldy for a serial network.

To monitor actual bandwidth usage including error frames would require a product such as the Brad Harrison NetAlert. Actual bandwidth usage can be monitored with an online connection and a software package called DeviceNet Traffic Analyzer which worked with 1784-PCD card however error fames are not included. Unfortunately the 1784-PCD card is no longer available. Knowledge base document 25155 - Using the DeviceNet Traffic Analyzer to determine network timing of a polled network discusses it usage. Encompass partner FrontLine offers an alternative to the DeviceNet Traffic Analyzer software.

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