Device Net Topics Slide for Basic Study and Understanding

Device Net Topics Slide for Basic Study and Understanding

1. •Application Layer Protocol
–Deals more with application data than lower level
non-application data
•Unlike a link layered protocol which simply moves some
bytes from point A to point B
–Messages do convey information
–Byte for class number, service code, etc.

2. •Controller Area Network
–Serial communication standard for intelligent
devices to communicate with each other
–Max rate 1 mega baud; usually set at 125 Kbaud
–Max transfer 8 bytes in a single frame
–Bitwise arbitration: prioritize messages without
losing bandwidth

3. •Communications and Interface Protocol (CIP)
–Transfers data between two devices
–Combined with CAN physical layer to create
DeviceNet
–Specifies ways in which data is accessed
•Cyclic, polled, change of state

4. •CIP Required Objects
–Identity Object: contains attributes that identify the
DeviceNetdevice
•Vendor ID, date of manufacture, serial number
–Message Router Object: exists to route explicit
messages and explicit responses to and from the
Connection Object
–DeviceNetObject: contains attributes that identify
port, baud rate, MAC ID (DeviceNetAddress), vendor
ID, and other physical properties
–Connection Object: contains attributes that control
the processing of specific I/O
•How often data is produced and the path to find data

5. •Application Objects
–Define the data encapsulated by the device
–Specific to the device type and function
•Motor: frequency, current rating, size
•Analog Input or I/O: type, resolution, current value
–All CIP devices with same device type must
contain the identical series of application objects
–Device profile: series of application objects for a
particular device type
–Can be grouped into assembly objects by vendor
•Contain attribute of one or more application objects

6. •Vendor Specific Objects
–Objects not found in the profile of the device
–Vendor calls these additional features
–Data of vendor’s choosing
–Organization of data vendor’s choosing

7. •Connections and Connection IDs
–For most devices it’s messaging between a master
and slave device
–Connection IDs predefined
–Two connection IDs allocated
•Produced: allocated for the message transmitted by
the device
•Consumed: allocated for the message consumed by
the device
–The lower the ID the higher the priority
•Use lower MAC IDs for high priority devices

8. •Unconnected Message Connections
–Virtual access port
–Provides a way for device to send a few
predefined messages to a DeviceNet device
without first making connection
–Limited to creating or deleting other connections
–Part of Group 2 Connection Set
•Used by slave devices

9. •Connected Message Connections
–Produced and consumed across a connection
between two devices
–Explicit/Request type
–I/O messages containing formatted data
–Transferred at a specific rate (cycle), on a response
(poll), or on a change of state (COS)
–May be public predefined data or proprietary data
specific to a vendor (proprietary peer message)

10. •Master Slave Connected Messaging
–Master devices gather input data from multiple
slave devices and distribute output data to the
slave devices
•Scanners or client devices
–Slaves can be referred to as servers

11. •I/O Connection Messaging
–Connections that distribute output data to and
gather input data from slaves
–Output data: data moved from the network into a
device
–Input data: data moved from a device into the
network

12. •Offline Connection Messaging
–Communication faulted state
•If on power up it detects another device with the same
MAC ID
–Unable to transfer any data or perform any
application operations until fault is cleared
–Typically cleared by re-addressing the network
–Offline connection set: a configuration tool can
connect to a faulted device, change its address
and reset it
•Few devices support this

13. •Peer to Peer
–Exchange of messages from one device to another
over any non-master/slave connection
–Most peer to peer is between same vendor
products
•Scanners in a scan tunnel where one tells the others it
has the barcode

14. •Explicit Messaging
–Request/response messages that are issued by the
master to request a service from a specific slave
over an explicit message connection
–Service code field identifies the requested service
–Remainder of message contains data required to
execute the service
–GET/SET most common messages

15. •I/O Messaging
–Transfer predefined I/O data between a DeviceNet
scanner and an I/O device
–Referenced from the point of view of the network
–Input: data point produced by an I/O device
–Output: data point consumed by an I/O device
–Device can have multiple input and output
assemblies

16. •I/O Messages
–Polled
•Request/reply messages issued to the polled
connection
•Sent by the scanner at a rate of its choosing
–Cyclic
•Scheduled messages
•Slave periodically issues messages to the master on a
fixed schedule
–Change of State (COS)
•Produces on an event
•Slave issues a heartbeat message to the scanner

17. •Scanner and Adapter
–Master and slave
–Explicit messaging uses fragmentation protocol
–I/O messaging does not use fragmentation
protocol
•Multiple messages transferred with no encoding
•Receiver simply reconstructs I/O data in the sequence
messages are received

18. •Connection Establishment Messaging
–Baud rates of all devices must match
•125K for 500 m/1640 ft
•250K for 250 m/820 ft
•500K for 100 m/328 ft
–Address must not conflict
•Media Access Identifier (MAC ID)
•Max 64 nodes on a network
–Addresses 0 to 63

19. •Duplicate MAC ID Sequence
–Specific messaging sequence and timing
–Duplicate MAC ID request message
•Vendor ID and serial number
•No two devices in the world can have the same serial
number from a vendor
–Sends a duplicate MAC ID one second appart
•If any online device responds with same MAC IC device
transitions to a fault status
•If no response is received the device remains on line

20. •Miscellaneous Messages
–Device shutdown message
•Optional message
•Broadcast of the fact that a device is transitioning to an
offline state
–Device heartbeat (DHB)
•Communication to the master that the device is
operational

21. •Error States
–Non-existent: device has shut down due to an
internal error or some remote command
–Unallocated: device has successfully joined the
network but is not currently owned by a master
•LED flashed GREEN
–Timed out: message failed to arrive on one or
more connections with master
•Recoverable
•LED flashes GREEN

22. •Error States (continued)
–Faulted: device has detected an internal error or a
Duplicate MAC ID respond message
•Not a recoverable error
•LED solid RED
–BusOff: device has detected significant network
errors and has removed itself from operation
•Typically a hardware failure in the device circuitry

23. •Device Types
–Master devices (scanners)
•Client devices
•Own slave devices: many or all
–Slave can only be owned by one master at a time
•Must first allocate a slave via handshaking messages
–Requests control
–Configures slave to transfer a particular set of data
–Open Explicit Request message issued on the unconnected
message port
–Usually requests both an explicit and an I/O connection
•Slave may deny a request if already allocated
•Scanning begins once the slave is fully configured

24. •Device Types (continued)
–Slave devices (servers)
•Receive and transmit application specific data to and
from the master
•Implement Predefined Master Slave Connection Set
•Slaves must support one or more of the following:
–Polling, Cyclic, COS

25. •Master Allocation Sequence
–Master issues an Unconnected Open Request
Message to the slave
•Slave that supports unconnected messages allocates an
Explicit Message connection and answers the master
•Slave returns a connection ID and describes the kind of
message it can support
–If slave fails to answer the unconnected message
request within one second, the master issues a
second request message
•Slaves that don’t support unconnected messaging will
ignore unconnected message requests

26. •Master Allocation Sequence (continue)
–A slave may answer the second request, allocate
an Explicit Message connection, and return the
connection ID to the master
–If a slave fails to answer both Unconnected
Message Requests the master waits another
second and issues a Group 2Only Connection
request
•Attempts an allocation of an explicit and/or I/O
connection using Group 2 Only port
–Slaves that fail to answer the Group 2 only request
are marked as faulted

27. •Master Allocation Sequence (continued)
–Using the explicit connection established with the
salve, the master configures the I/O connection
•Sets I/O time out, connection paths, other attributes
–Once I/O connection is complete some masters
will delete the explicit connection since it is no
longer needed

28. •Physical Media Issues
–Indicators and switches
•Configured using external hardware and software tools
–Hardware: rotary switches, thumbwheels, dip switches
»Easily replace
–Software: access configuration of device over net or through
a port
»Greater configuration capability
–Termination
•Resistor at the end of each trunk
•¼ watt, 120 ohm resistor placed between the CAN-L
and CAN-H signals
–Isolation when using external power supplies