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Issue
99, October 1998
Networking
with DeviceNet—Part
2: A Weather Station Application
by
Jim Brady
Start
• Can
Chips
• Chip
Setup •
Real Time
• Message
Flow
• Connections
• Timers
• Analog
Input Point
• Identity
Object
• Fragmented
Messages
• Getting
Physical
• Applying
DeviceNET
• Software,Sources
CONNECTIONS
Connections
have states other than nonexistent and established, and
some are unique to one or the other connection. This setup
is so confusing, I made a state transition diagram. Figure
2 combines the behavior of both types of connections,
using colors to tell them apart.
When
the master allocates the Explicit connection, the connection
simply transitions to the established state and it’s
ready to use. The connection timer starts at 10 s.
If
it times out, the connection goes to one of two possible
states depending on whether the connection is in autodelete
or deferred-delete mode. In autodelete mode, if it times
out, it’s gone. In deferred-delete mode, it stays
around and goes back to the established state if a message
comes in.
The
I/O connection, when allocated, goes to the configuring
state. In this state, it cannot process I/O messages and
must wait for the master to set its expected packet rate
via the Explicit connection. Then it is in the established
state and can begin handling I/O Poll requests.
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