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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
APPLYING
DeviceNET
In addition to all of the
objects for DeviceNet, you need code for your application.
The weather station is simple enough that I just extended
the Analog Input Point object. It reads the ADC and computes
sensor values.
If you have separate application
objects, you must link them with the Identity object.
It keeps track of device status and does resets. A standard
object used for SEMI-compliant devices, the S-Device Supervisor,
is designed to do this.
This article is mainly about
DeviceNet, but the weather station’s details are
on the Circuit Cellar web site. I hope to add sensors
for barometric pressure and wind speed and build units
for other locations.
My network master is a ’486
with a DeviceNet card from Softing GmbH. It comes with
a library that makes it easy to use. Also check out National
Instruments’ card which works with LabVIEW and CVI.
Aside from being a fun combination
of real-time software and hardware, this project shows
how straightforward it is to program a DeviceNet interface
in C++. With a little care, C++ can provide good response
times and reasonable program size.
Jim Brady has designed
embedded systems for 15 years. You may reach him at jimbrady@ix.netcom.com.
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