Rockwell Automation 1791-XXXX Discrete I/O AC and DC Block I/O Input and Output Modules - Manual (Page 66)

Configuring Your Block I/O for PLC
Family Programmable Controllers
Chapter 4
4-9
PLC-2 and PLC-5 family processors support a complementary I/O
configuration. Complementary I/O can allow you to maximize memory
usage without increasing memory size. Refer to the user’s manual for your
processor to see if it supports this type of configuration.
You configure complementary I/O by duplicating an I/O rack number of
one I/O chassis (primary) in another I/O chassis (complementary), 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.
Important: Series A block I/O modules do not support complementary
I/O. If using complementary I/O, use series B modules.
When using I/O racks in a complementary configuration, the block I/O
must be paired with a device which occupies 1/4 rack of I/O space (i.e.
primary and complementary must be the same logical rack size).
Note: The 1747-SN series A is not capable of supporting
complementary I/O.
Figure 4.11
Processor Data Table Use with Complementary I/O
To Programmable Controller
or I/O Scanner Module
1 I/O Rack -
with
Complementary
I/O
10833ĆI
16Ć or 32Ćpoint
Output Block I/O
16Ć or 32Ćpoint
Input Block I/O
16Ć or 32Ćpoint
Input Block I/O
16Ć or 32Ćpoint
Input Block I/O
16Ć or 32Ćpoint
Input Block I/O
16Ć or 32Ćpoint
Output Block I/O
16Ć or 32Ćpoint
Output Block I/O
16Ć or 32Ćpoint
Output Block I/O
Input Block and Output Block
on each pair have the same
logical address.
Install terminating resistor on last block.
Using Complementary I/O