Complementary I/O - Allen-Bradley 1747-SN User Manual

1–10 Overview
Publication 1747 6.6 - July 1996

Complementary I/O

Complementary I/O is very useful when portions of your input and
output images are unused because it allows the images of two
adapters to overlap each other in the scanner's I/O image. To use
complementary I/O, the I/O image from one adapter must be the
mirror (complement) of the other. This means that there must be an
input module in the primary chassis and an output module in the
same slot of the complementary chassis. This enables total use of the
scanner's 32 input and 32 output word image for I/O addressing of
up to 1024 discrete points.
ATTENTION: Because the primary and
complementary chassis images overlap, input and
!
specialty combination I/O modules must never share
the same image location. Inputs received by the
scanner may be incorrect and RIO block transfers will
not be serviced properly.
If an output module shares its output image with
another output module, both output modules receive
the same output information.
If you want to use complementary I/O, two adapters that support
this function are required (e.g., 1747-ASB modules). One adapter is
configured (via its DIP switches) as a primary chassis, the other as a
complementary chassis. If a primary chassis exists, it is scanned
first.
Primary and complementary chassis cannot have the same logical
rack number. The logical rack numbers must be assigned to the
primary and complementary racks as shown below:
Primary Chassis Primary Chassis
Logical Rack Number
0
1
2
3
Complementary Chassis Logical Rack Number
Decimal
8
9
10
11
Octal
10
8
11
8
12
8
13
8