Allen-Bradley DeviceNet 1761-NET-DNI, User Manual, Page: 25 / 101

1761-6.5
Operation 3-3
Explicit Messaging Services
The capabilities of each individual device determine what level of
messaging is supported. The types of messaging supported are:
•
I/O Assembly Messaging (DNI responds) (see below for more
information)
•
PCCC encapsulated DeviceNet Messaging (peer-to-peer) (see page 3-4
for more information)
•
Explicit Assembly Messaging (DNI initiates, DNI Series B only) (see
page 8-1 for more information)
I/O Assembly Messaging
Two conditions must be met to access the I/O assemblies:
•
Data Enable (DNI Series A) or I/O Scan Enable (DNI Series B) must be
enabled.
•
The DF1 Device must be servicing the Heartbeat. See "DF1 Heartbeat"
on page 5-15 for information on using the Heartbeat.
The following sections describe additional conditions based on the DNI
Series.
DNI Series A
DNI Series A supports explicit messaging to the master I/O assemblies over
DeviceNet at a minimal level. If the DNI is not owned by a DeviceNet
master, the DNI responds to explicit messaging gets and accepts explicit
messaging sets to the master I/O assembly. If the DNI is owned by a
DeviceNet master, it responds to gets, but cannot accept sets. In either case,
the data size must be 16 words, even if the I/O size is smaller. See page 6-12
to address DNI Series A assemblies.
The DNI Series A cannot perform get/set attribute I/O messaging over
DeviceNet; it can only respond.
DNI Series B
DNI Series B provides the above described functionality, except the data
size is equal to the configured I/O size. Additionally, DNI Series B can
respond to explicit messages over DeviceNet to its explicit I/O assemblies
whether it is owned by a DeviceNet master or not. See page 6-13 to address
DNI Series B assemblies.
DNI Series B can also perform get/set services with its new DeviceNet
messaging capability. See "Explicit Messaging Examples" on page 8-3.
AB Parts