Appendix A: DeviceNet
®
Secondary Communication
34
3A7639A
About DeviceNet
DeviceNet is a connection-based network. In this con-
text the term connection refers to a communication path
between two or more devices, and not the physical
(cable) connection to the DeviceNet network. A connec-
tion must be established between two devices in order
to transfer data.
There are two types of connection defined by the Devi-
ceNet specification. Each has different characteristics
and is suited to a specific type of communication.
•
I/O Connection
– Dedicated data transfer between
a producer and one or more consumers. The format
of the data is known or implied by the connection.
•
Explicit Messaging
– Generic multi-purpose mes-
saging connection, typically command and
response message commands.
Each connection type has an extensive number of
parameters, which can affect the characteristics of the
communication path. For many Priority/Secondary com-
munications scenarios, a defined set of connections,
together with their respective parameter settings exist
under the collective name Predefined Priority/Second-
ary Connection Set. Many of the steps involved in creat-
ing and configuring a connection have been removed
with this connection set, thus simplifying the network
configuration.
Predefined Priority/Secondary Connection
Set
The DeviceNet specification details a number of con-
nections that facilitate data transfer between a Priority
and Secondary devices. The following sections detail
the connection types supported by the Gateway Assem-
bly.
•
I/O Bit-Strobe Connection:
The Bit-Strobe connec-
tion is an I/O connection over which Bit-Strobe I/O
command and response messages are transferred.
The Bit-Strobe command is broadcast by the Prior-
ity device and is received by all Secondary devices
simultaneously. The command message contains a
single bit of information for each Secondary on the
network. Each Secondary device is required to
respond with a Bit- Strobe response message. The
response message can contain up to 8 bytes of
information.
•
I/O Poll Connection:
The Poll connection is an I/O
connection over which Poll command and response
messages are transferred. The Poll command is
transmitted by the Priority, and is directed to a sin-
gle Secondary device. The Secondary device in turn
responds with a Poll response message. Both the
Poll command and Poll response messages can
contain any number of bytes.
•
I/O Data Connection:
The I/O Data connection is
part of the Predefined Priority/Secondary Connec-
tion Set, but instead is included for devices, which
support creating I/O data connections via the
UCMM (Unconnected Message Manager).
Level of Support
The Gateway provides Group 2 Server level support: A
UCMM capable device that is configured to act as a
Secondary
for the Predefined Priority/Secondary con-
nection set.
Refer to your Crimson 3.1 User Manual for use and con-
figuration of this DeviceNet card.
