Rules For Configuring The Scanner; General; Concerning Complementary I/O - Allen-Bradley 1747-SN User Manual

Scanner Configuration and Programming

Rules for Configuring the Scanner

General

The smallest portion of the scanner's I/O image that can be allocated
to a single RIO device is two logical groups (1/4 logical rack).
If a device is configured in word 1, there must be image allocated
to it in word 2. This rule also applies to words 3 and 4 with the
following exception: if word 3 = 1 and word 4 = 0, the
complementary mode is selected even though no complementary
devices are configured.
A logical device's starting group must begin at even group
numbers
(0, 2, 4, or 6). Each bit in words 2 and 4 represent an even logical
group number.

Concerning Complementary I/O

It is valid for you to have a complementary device configured
even if no associated primary device exists. Also,
complementary devices do not have to be the same logical image
size as the primary device.
G file words 1 and 2 can both be zero (no primary devices).
However, in this case there must be at least one complementary
device configured in G file words 3 and 4.
If there is at least one primary device configured in G file words 1
and 2, words 3 and 4 can both be zero, or the G file size can be
set to 3 (complementary mode not selected).
The starting group of the primary and complementary chassis
should be the same if they share the same image space. If the
starting group is not the same, the image of the complementary
device must not "cross over" into the space of a primary device.
For example, if a primary device exists at Logical Rack 1 Logical
Group 4, the maximum size of a complementary device at
Logical Rack 9 Logical Group 0 is a half logical rack, so its
image does not cross over into Logical Group 4.
A complementary device cannot be configured at locations where
primary devices are configured unless they both start at the same
location.
If you configure your system so that complementary I/O is not
selected (words 3 and 4 are zero), you must not set up any of the
actual devices to be in the primary mode. If you do, the system
will flag the device as faulted and prevent the device from
running.
Control functions (i.e., device inhibit, device reset, and device
output reset) are only selectable for the primary device, but also
apply to the complementary device. Control functions for
complementary devices cannot be exclusively enabled.
4–5
Publication 1747 6.6 - July 1996