Rockwell Automation 1747-SN Remote I/O Scanner - Manual (Page 51)

Publication 1747-UM013B-EN-P - January 2005
Scanner Configuration and Programming 4-7
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.