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2. April 2013 TechConnect Genius Webinar
Demystifying DeviceNet: Stability and Performance Tips
Rod Shearer
Commercial Engineer
April 25, 2013

3. DeviceNet: Book of Knowledge Index
Knowledgebase document:
Slide DeviceNet Ten Commandments
6 Who You Gonna Call??
12 Selling DeviceNet
23 Physical Layer (Media)
68 Hazardous Environments
70 Slip Rings
76 Automatic Device Replace (ADR)
79 Media Access (Data Delivery)
91 Network Installation Check List
92 Protocol Details (Application Layer)
105 Important Concepts, Proxy and EPR
107 DeviceNet Products
109 RSNetWorx for DeviceNet
113 Faulted Address Recovery
KFD
U2DN
PCD
SDN
SDN
DNB
SDN
DNBO
CN2DN Bridge
EN2DN Bridge
DNENCATR Bridge
PCID & PCIDS
DNET Pico Interface
179 Scanner Error Codes
182 Network LED Definition
184 Uploading EDS Files from Scanners
186 Scanner Archive Ladder Logic
189 Node Commissioning Ladder Logic
191 Slave Mode for Scanners
194 Passthrough Feature for Scanners
Rod Shearer
Bob Law
AKA Dr. DeviceNet

4. DeviceNet: Book of Knowledge Index (continued)
Knowledgebase document:
195 Shared Inputs for Scanner
198 Quick Connect
201 AutoScan for Scanners
204 RSLogix 5000 Tag Generator
205 Online Changes At Run (OSCAR)
206 Easy Backup
209 DeviceLogix Feature for I/O devices
217 Zone Interlocking Parameters
224 Series 9000 Photoeye
EF RightSight Photoeye
TM Prox
DN Limit Switch
D DeviceLink
Pendant Station
E Pushbutton Stations
F Pushbutton Stations
RediSTATION
D MaXum I/O ArmorBlock
D ArmorBlock
Classic ArmorBlock
Low Profile ArmorBlock
and 1791 CompactBlock I/O
281 Bulletin 100 DSA
Embedded I/O
ADN Remote IO Adapter
PointBlock I/O and Point I/O
Adapter Selection Guidelines
ASC ASCII to DeviceNet
CFGDLX IO Module
ArmorPoint I/O
ADN Flex I/O
Tower Light
336 Bulletin 160 Drive
E3 & EDN Smart Overload
Slide ArmorStart Products
GK5 and GU6, 2100-GK61
364 PowerFlex Drives
367 CIP Safety and Safety Products
D Absolute Encode
NET-DNI
384 XM Products
387 PanelView
391 PanelView Plus
392 Explicit Messaging
413 DDE/OPC Data Transfers
417 DTAM Micro and Plus
420 Bulletin 825 and Bulletin 150
423 PowerMonitor II
429 Ultra 100 Servo Drive
Motion Control
P Motor Protection Device
PCT and 193-DNCT Hendheld Configurators
443 Network Performance
449 Traffic Analyzer
450 Integrated Architecture Builder
451 Troubleshooting Tips
453 Molex NetAlert NetMeter
455 DeviceNet Detective

5. Agenda Network Installation Network Performance
Tuning Network Performance
Troubleshooting Summary

6. Agenda Network Installation Network Performance
Tuning Network Performance
Troubleshooting Summary

7. Did You Know?
You can solve 95% of all DeviceNet issues using the information in the DeviceNet Media Design and Installation Guide!
Search for DNET-UM072

8. Termination Resistors
Termination resistors are 120 or 121 ohms, 1/4 watt or larger
You MUST place them at each end of the trunkline between White (CAN_High) and Blue (CAN_Low) wires
Do not use carbon resistors!! Metal film is preferable.
How do I verify proper network termination?
Remove network power.
Measure impedance between white and blue wires.
Impedance value should be between 50 and 60 ohms.

9. Max Total Trunk Distance: 500m @ 125Kb (thick cable)
Network Topology (Trunkline - Dropline)
Max Total Trunk Distance: 125Kb (thick cable)
Terminator
Trunk
Tap
Terminator
Node
Node
Node
Drop
Length
Node
max
6 m
Power
Supply
Node
Node
Separating the two termination resistors is the DeviceNet trunkline in the trunkline-dropline topology.
Maximum trunk distance is dependent on cable type and baud rate. Maximum distance is available with thick media at the slowest baud rate: 125k; at 500k max distance for thick cable is 100m.
The Taps shown in the image are passive and are not needed. Taps are available for sealed and open style conductors to simplify and protect field wiring.
Maximum drop length is 6m for all cable types regardless of media type; there is no minimum drop length
Maximum cumulative drop length varies by baud rate but is the same for all media types. 125k; 500k
Reference DNET-UM072 for details.
A common question is: What happens if my network includes a mix of cable types? Use the weakest link rule and follow the guidelines for the media with the shortest distance. For example if Thick cable is mixed with Flat media follow the guidelines for Flat media because it has shorter distance ratings.
When routing cable ensure proper spacing from noise sources such as AC voltage. Reference publication for specifics.
Node
Node
Daisy Chain
Drop
Branching Drop
Zero Drop
Power & signal to all devices on a single cable!

10. Guidelines for DeviceNet Power
11-25 V DC supported voltage range
Locate toward middle of network
Current adequate, limited and protected
Rise time < 250ms to within 5% of rated output voltage
How do I verify if power supply is associated with Bus Off error on power up?
Cycle DC power at the supply.
If Bus Off does not occur, this is a sign that the power supply is out of spec.
If Bus Off still occurs, keep looking as other issues exist.
Adequate current means the power must be available for all devices. Don’t forget distance does matter which is why the suggestion is to locate the power supply in middle of the network.
All devices consume >= 60 mA for DeviceNet transceiver. Some devices such as photoeyes draw all their power from the network.
If necessary multiple power supplies may be used.
When in doubt look for ODVA checkmark to ensure that products are approved.

11. Network Grounding
V- (Black Wire) and Shield (Bare Wire) MUST be connected to a good earth ground at only one location on a DeviceNet System
Ground connection should be accomplished with at least an 8 gauge conductor no longer than 10 feet long.

12. V+ to V- < 15VDC is cause for concern
Common Mode Voltage
Network issues can occur due to current draw coupled with distance; V = I * R
V+ decreases from 24VDC and V- increases from 0VDC with distance
CAN_H (White) and CAN_L (Blue) reference V-
V+ to V- < 15VDC is cause for concern
Integrated Architecture Builder software can identify Common Mode Voltage issues at design time

13. DeviceNet Network Installation Checklist
Termination resistors (1 at each end of trunk)
Grounding of Network (One location only)
Cumulative drop line budget in spec. for selected baud rate
Spacing guidelines from AC cables –
No Drops > 20 feet (6 m)
Trunkline budget in spec. for baud rate
Total Network Current Check ( Integrated Architecture Builder )
Common Mode Voltage Check at network ends, with full load present
Voltage and Ohm readings of CAN wires within specification
Proper termination: verified by removing network power and measuring 60 ohms between Can_L (blue) and Can_H (white)
Proper grounding: Verified by removing network power and lifting the ground and ensuring that ground is not connected.

14. Agenda Network Installation Network Performance
Tuning Network Performance
Troubleshooting Summary
When considering Network Performance it is important to consider the different communications that exist such that the correct balance can be found that allows IO updates and other traffic to coexist while meeting application requirements.
Although most networks are fine with the default settings some will require tuning. My philosophy is: “If it ain’t broke don’t fix it.” Start with the defaults and only apply tuning when necessary.

15. Communication Options
Poll / Strobe Model
Strobe R 3 P 4 2 1 5 P6 6 I S D
Cos 6
Cos 1
Cyc 2
Change
COS / Cyclic Model
DeviceNet is a Master / Slave network with the DeviceNet Scanner being the Master and other devices in the scanlist as Slaves.
Polled mapping is the most common and simplest to understand with slave devices responding when spoken to by the Master scanner.
Strobed mapping is similar to Polling but only allows input data.
COS mapping can increase network bandwidth and performance for devices where data does not change frequently compared to Polling. However COS can decrease network bandwidth and performance where data changes frequently such as with Analog devices.
Cyclic mapping is best applied to devices whose data changes slowly and where repeatable performance is a benefit.
Explicit Messaging can provide read/write access to information within a device on DeviceNet that is not normally available as I/O data. A benefit of explicit messaging is that bandwidth is only consumed when it is used instead of every scan as with polled data.
DeviceNet allows for all communication types to be combined on the same network.
Important: Not all devices support all communication options. Reference device documentation for verification of what is supported.
What gets to communicate and when is handled by the protocol through prioritization and arbitration.
EXP SW D 1 SW D 1 SW SW P 4 D 1 SW P 5 D 1 R 4 R 5 SW P6 D 1 SW R 6 D 1
EXP
Module configuration; Explicit Messaging

16. Communication Prioritization
Group 1
Slave Change of State (COS) / Cyclic, Strobe, Poll or COS / Cyclic Ack
Group 2
Master Bit Strobe, COS / Cyclic Ack
Slave Explicit Unconnected Message Response
Master Explicit Connected Message Request
Master Poll, COS / Cyclic
Group 2 only Unconnected Message request
Duplicate Node ID check <occurs for all device on powerup>
Group 3
Unconnected Explicit Message Response and Request
Network Configuration; Upload/Download
Group 4
Diagnostics
The communication options are segmented into 4 groups with types within each.
Group 1 has the highest priority followed by Groups 2, 3 & 4
Group 1 traffic is associated with Slave communication
Group 2 is mostly associated with Master communication
Group 3 is associated with Explicit Messaging and for Software configuration
Group 4 is used for protocol diagnostics and is not common used.
For example Group 1 slave COS type has a higher priority than Group 1 Strobe.

17. Media Access and Arbitration
Node Y’s Transmission
Node “Y”
Network Latency Time
Node X’s Transmission
Node Z’s Transmission
Interframe
Space
> 3 bit times
If a transmission is occurring a node must wait until it is complete before attempting to transmit.
Lowest node # wins which is why scanner is typically assigned node 0 and communication device is assigned node 62
Node 63 is left open for new devices to be added to the network.
Time
Message Group / Type is used to determine who is allowed to communicate
If Message Group / Type is the same, the lowest node number wins 25

18. Provides time for slave response packets and explicit message packets
InterScan Delay (ISD)
Provides time for slave response packets and explicit message packets
Begins after the scanner sends the last outgoing polled packet
If the ISD is too short, the network can become starved for bandwidth and erratic operation could occur
Guideline: ISD (milliseconds) = (BYTES / 7)* ; BYTES = summation of last two devices input poll data
Scanner idle allows time for slave response packets and explicit message packets
Begins after the scanner sends the last outgoing polled packet
If the ISD is too short, the network can become starved for bandwidth and erratic operation could occur because devices can be prevented network access due to arbitration and experience timeouts.
Guideline: ISD (milliseconds) = (BYTES / 7)* ; BYTES = summation of last two devices input data
The 7 in the ISD guideline is because Dnet supports max of 8 bytes of data per packet. If data size > 8 bytes fragmentation is used with 1 byte associated with fragmentation handling.
Max data size for DNET comms is 255 bytes / 7 = 36 DNET packets.
Slave devices may be overwhelmed by the speed of updated / newer scanners that communicate faster – ISD can be adjusted to decrease the frequency of scanner communications.
Poll / Strobe Model
Strobe R 3 P 4 2 1 5 P6 6 I S D 31 19

19. Expected Packet Rate (EPR)
How long to wait until closing connection?
Default Timeout Polled / Strobed = 75 X 4ms = 300ms
Default Timeout COS = 4 X Inhibit Time = 1000ms
Default Timeout Cyclic = 4 X Send Rate = 4000ms
Timeout for Poll & Strobe device communications = 4 * EPR
Timeout for COS device communications = 4 * Heartbeat rate
Timeout for Cyclic device communications = 4 * Send rate
Let’s take a look at an RSNetworx for DNET application and see where these and other Advanced settings are available.
Changing EPR affects how long it takes for timeout to be declared and connection timed out – exercise caution when changing this value 31 19

20. Agenda Network Installation Network Performance
Tuning Network Performance
Troubleshooting Summary
When considering Network Performance it is important to consider the different communications that exist such that the correct balance can be found that allows IO updates and other traffic to coexist while meeting application requirements.
Although most networks are fine with the default settings some will require tuning. My philosophy is: “If it ain’t broke don’t fix it.” Start with the defaults and only apply tuning when necessary.

21. Tuning Network Performance
Use maximum baud rate for system installation
Minimize ladder scan time
Minimize backplane time by decreasing RPI
Reduce slave device data size
Use Change of State devices on the network for higher priority I/O devices
Use inhibit time for COS devices data is changes frequently
Use maximum baud rate for system installation
Minimize ladder scan time
Minimize backplane time by decreasing RPI
Reduce slave device data size
Use Change of State devices on the network for higher priority I/O devices
Use inhibit time for COS devices data is changes frequently

22. Agenda Network Installation Network Performance
Tuning Network Performance
Troubleshooting Summary

23. Troubleshooting Steps
What changed?
Does the issue occur at any particular time? On Power up? When starting a motor?
Does the error code indicate network or configuration issue?
Is the error associated with all nodes or only a few?
Are the affected nodes in the same network section? 27

24. Troubleshooting Network Issues
Verify proper termination between 50 – 60 ohms with network power removed
Verify Grounding – find single ground point and remove it. Verify >1M ohm
Inspect Power – V+ separated for multiple supplies
Common Mode Voltage; >15VDC between V+ and V- at furthest distance from power supply with full load applied
Verify Network Voltages
Master removed Can_H & Can_L reference to V- between 3.0 and 2.5 VDC
With Master Active Can_H to V- = 3.2VDC; Can_L to V- = 2.4VDC
Check wiring – walk the network looking for items of concern
Bad hardware? Try to limit the variables and simplify the network by removing nodes, drops, segments of trunk 27

25. Bus Off Condition Indication: Why:
Solid red network LED on a slave device
Bus Off or 91 error scanner front display
Why:
DeviceNet products monitor network for stability with received frame bad counter
Error counter increments on received bad network frames and decrements with good
Bus off occurs when counter gets too high which indicates that the network is not stable and shuts itself down. 27

26. Bus Off Condition Causes: DNET-UM072 rule being broken
Improper termination
Intermittent connection on CAN lines causing short or open circuits
Power supply rise time too slow
Cable lengths exceeding maximum trunk or drop lengths (individual or cumulative)
Electrical noise on network
Mismatched baud rate
Defective device(s) sending bad frames
When all else fails, call Tech Support: 27

27. References 48833 DeviceNet Book of Knowledge
DNET-UM072 DeviceNet Cable Planning and Installation Manual
Industrial Automation Wiring and Grounding Guidelines
Integrated Architecture Builder
16582 ADR – Frequently Asked Questions
17536 How to Configure ADR
42966 Finding and Installing EDS Files
20862 DeviceNet Performance – Approximating Wire Time
25158 Understanding DeviceNet Network Performance, Bandwidth Utilization and Interscan Delay
15075 Troubleshooting DeviceNet
RA-UM003 DeviceLogix System User Manual
Rockwell Automation Literature Library
Open DeviceNet Vendor Association 27