Rockwell Automation 1756-RIO ControlLogix Remote I/O Communication Interface Module User Manual - Manual (Page 84)

84 Publication 1756-UM534B-EN-P - November 2010
Chapter 4 Link Module Configuration with RSLogix 5000 Project
Aliases Aliases are used to access data in the ControlLogix system. They define the
names and descriptions exported from the configuration program and
imported into the RSLogix 5000 control program and should be used for
adapter and scanner modes.
Aliases are symbolic names that point to I/O data. The configuration tool
creates these aliases for discrete and block transfer data based on the I/O
mappings. It is important that you develop the control program in the
RSLogix 5000 project with reference to aliases as opposed to absolute
addresses. Then, if the mappings change, the ControlLogix controller still
operates; you just create aliases for the new mappings by exporting them from
the configuration tool and re-importing them into the control program, which
then points to the new data.
Also, it’s important to note that export options in the configuration tool differ
depending on whether you have your 1756-RIO module set for scanner or
adapter mode.
In this section, you will cover:
• exporting aliases in scanner mode.
• exporting aliases in adapter mode.
• using the Export Aliases command in the configuration tool to upgrade
an existing system to a ControlLogix system.
EXAMPLE
For example, let’s say you’re mapped rack 7 inputs to block 0,
offset 8, so the data for rack 7, I/O group 0, is at input address
I0:[10]. Now you add a rack 6 and remap everything so that now
the rack 7 input data maps to block 0, offset 20.
The data for rack 0, I/O group 0, now moves to I0:[22].
If you had used absolute addresses in your control program, you
would have to re-address every instruction in the program. By
using aliases, you can use the Export Aliases command from
the configuration tool and import them into the RSLogix 5000
project, which automatically points to the new data.
IMPORTANT
You must export the new aliases from the configuration tool
and import them into the RSLogix 5000 project before you run
the program; otherwise, you could read wrong inputs and/or
write wrong outputs.