Rockwell Automation 1785-LTx,D17856.2.1 Classic PLC-5 Programmable Controllers Users Manual - Manual (Page 54)

Assigning Addressing Modes,
Racks, and Groups
Chapter 4
4-12
You configure complementary I/O by assigning an I/O rack number of one
I/O chassis (primary) to another I/O chassis (complementary),
complementing modules I/O group for I/O group. The I/O modules in the
complementary chassis perform the opposite function of the corresponding
modules in the primary chassis.
The PLC-5/15 and -5/25 processors operating as a remote I/O scanner
support complementary I/O.
Use these guidelines when you configure your remote system for
complementary I/O:
Assign the complementary I/O rack number to a chassis of any size.
Do not place an input module opposite an input module; they will use
the same bits in the input image table.
You can place an output module opposite another output module; they
use the same bits in the output image table. This allows you to use one
output module to control a machine and use the other module with the
same address to control an annunciator panel to display the machine
condition. We do not, however, recommend this placement of modules
for redundant I/O.
You cannot configure the PLC-5 processor-resident local chassis with
complementary I/O. The PLC-5 processor communicates with each
processor-resident local I/O chassis as if it were a full I/O rack (eight
I/O groups). Thus, if the processor-resident local chassis contains four
I/O groups, the remaining four I/O groups of that I/O rack are unused;
you cannot assign them to another chassis.
You cannot use complementary I/O with a chassis that uses a
combination of 32-point I/O modules and 1-slot addressing or 16-point
I/O modules with 2-slot addressing.
Important: For the PLC-5/15 and -5/25 processors, an autoconfigure is
performed before the scanner begins communicating with the adapter.
Placing the Modules with 2ĆSlot Addressing
Figure 4.5 shows a possible module placement to configure
complementary I/O using 2-slot addressing.
Addressing
Complementary I/O