Rockwell Automation 1760-DNET Pico DeviceNet Communications Module User Manual - Manual (Page 33)

Publication 1760-UM003A-EN-P - September 2005
DeviceNet Functions 4-9
DeviceNet Communication
Profile DeviceNet is based on a connection-oriented communications model,
that is data are exchanged only via the specific connections assigned
to the units.
DeviceNet stations communicate either by means of I/O messages or
explicit messages.
I/O Messages
I/O messages are used for exchanging high-priority process and
application data across the network. Communication between
DeviceNet nodes is based on the client/server model, i.e. a "producer"
application transfers data to one or several "consumer" applications. It
is quite possible in this case that several application objects are
addressed in the same unit.
Prerequisite for communication between the units via I/O messages is
the implementation of an I/O Messaging Connection Object. You can
activate this function in two ways:
• Either by means of a static and in the unit already existing ‘I/O
connection object’ or via the ‘Predefined Master/Slave
Connection Set’, or
• via a dynamically configured ‘I/O connection object’, which you
can configure using an Explicit Messaging Connection Object
that already exist in the unit.
Explicit Messages
Explicit messages are used for exchanging low-priority configuration
data, general management data or diagnostics data between two
specific units across the PtP connection in a client/server system, in
which the server always has to acknowledge client requests.
Same as for I/O messaging, the prerequisite for explicit messaging is
the implementation of a Connection Object, namely the Explicit
Messaging Connection Object. This can be achieved either by
activating an existing static connection object in the unit, or via the
Predefined Master/Slave Connection Set, or dynamically across the
UCMM port (Unconnected Message Manager Port) of a device.
All data of the function relay (Pico basic unit) are processed by means
of explicit messages. The DeviceNet master can thus read/write access
the parameters of the following functions.