Rockwell Automation DEVICENET 1771-SDN, User Manual

Page: 30 / 139

Publication 1771-6.5.132 - June 2000
2-2 Planning Your Configuration and Data Mapping Your Devices
A very important question to answer is “what is on your network?”
You should be familiar with each device’s:
•
communication requirements
•
I/O importance and size
•
frequency of message delivery
You should also ask “how might this network appear in the future?” At
this point in your planning, it is advantageous for you to have some
idea of how the network could be expanded. I/O data mapping can
be performed automatically by the RSNetWorx software. But when
mapping your I/O, you also have the opportunity to allot room for
future I/O. This can save time and effort in the future.
For example, RSNetWorx will automatically map the devices as
efficiently as possible, but the result is that multiple devices may share
the same word location in memory. However, you can also have the
system map the devices such that no two devices share the same
memory location by selecting the “Dword align” option when
performing automapping. You can manually map the devices if you
need to assign them to specific memory locations.
For details refer to the Help screens provided by the RSNetWorx for
DeviceNet software. Additional support can be found at the Rockwell
Software website: http://www.software.rockwell.com.
The Example Network
The following example illustrates a data mapping plan for a
DeviceNet network. Note that even if the mapping is performed
automatically by the RSNetWorx software, you must know where the
devices are mapped in order to use them in your network.
Example Network Devices
This example network has the following devices:
•
a PC running RSNetWorx for DeviceNet software
•
a 1771-SDN Scanner module interfacing a PLC-5 processor with
DeviceNet
•
a Series 9000 photoelectric sensor (strobed)
•
a RediSTATION operator interface (polled)