Rockwell Automation 1785-Lx0C15 ControlNet PLC-5 Programmable Controllers User Manual - Manual (Page 61)

1785-UM022C-EN-P - February 2008
Planning to Use Your ControlNet PLC-5 Processor 2-23
Optimizing the I/O Image Table
You may find that you are close to the I/O image table limits in a
PLC-5 processor and need to optimize the use of the I/O image table
in order to insure that the application will fit in the processor. This
section discusses techniques that make optimal use of the I/O image
table available in a PLC-5 processor. The use of these techniques is
not required, they merely demonstrate methods which can be used to
make maximum use of the available I/O image table. Proceed with
caution when using these techniques.
Important: You need to understand the ramifications of how you
map the I/O before proceeding, as the method you use
may make future expansion extremely difficult.
There are two methods to optimize the use of I/O image table in a
ControlNet PLC-5 processor.
• optimizing without slot complementary
• optimizing with slot complementary — where you set the I/O
chassis backplane switches to a lower density than the modules
you are actually using, and then staggering the modules: input,
output, input, output, etc. For example, you can set the backplane
switches to 2-slot addressing and then place 16-point I/O modules
in the rack: input, output, input, output, etc. See Configuring
Complementary I/O for PLC-5 Processors, publication number
1785-6.8.3, for information about slot complementary I/O.
Both methods make use of arranging the I/O modules in the most
efficient manner within the chassis.
In many cases, the optimal solution for a system is a combination of
both the methods.
Optimizing the I/O Image Table without Slot Complementary
The techniques used for I/O image optimization are best illustrated
using examples. The following examples all assume 1-slot addressing
for all chassis and that the local rack is using rack 0 image table
(I:000-007 and O:000-007).
Example 1
Examine the following chassis:
ACN I O O I O O
I = Discrete Input Module
O = Discrete Output Module
ACN = ControlNet adapter
X = Empty Slot
X X