NORD Drivesystems BU0080 - Manual (Page 16)

NORDAC DeviceNet Manual
16 BU 0080 GB
3 The DeviceNet protocol
Participants Up to 64 participants can communicate with each other in a DeviceNet network. Each
participant has its own node address.
Communication,
connection objects Communication between the individual devices is carried out via connection objects.
Before the exchange of data can start, these connections (Connection Objects) must
be set up.
Predefined Master/ Slave
Connection Set The Predefined Master/ Slave Connection Set provides an interface with which a set
of up to 4 connections can be allocated:
Explicit Messaging Connection
Polled I/O Connection
Bit.Strobe I/O Connection
Change Of State / Cyclic I/O Connection
Access to the slave is only possible from a Master.
Object model DeviceNet describes all data and functions on the basis of an object model. An object
represents the individual components within a device.
It is determined by its data or characteristics (attributes) and provides functions or
services (Services) for external access. An object class defines all characteristics
(attributes/services) for objects of the same type. With the creation of an object
instance, a real copy of the object with its own data is created.
Explicit Message Via Explicit Messages , low priority configuration or diagnostic data are exchanged
(parameterisation). This connection is always a point-to-point connection according
to the Client/Server principle.
I/O Messages I/O Messages are used to transfer process data. An I/O Message always has a
producer (transmitter). However, several consumers (recipients) may exist. The
process data can contain either 8 Bytes (unfragmented) or can be distributed
(fragmented) over several telegrams.
Polling A Polled connection corresponds to a Master-Slave connection: The Master send
cyclical data to the Slave. This then responds with its status data.
Bit-Strobe In aBit-Strobe connection, the Master sends an 8 Byte telegram to all connected
devices. Each participant is allocated exactly one bit. As all participants receive the
telegram simultaneously, a synchronous reaction can therefore be carried out. The
reaction of the individual participants is specific to the application and must be known
to the Master. Bit-Strobe telegrams are not confirmed.