Rockwell Automation 1771ACN/B_1771ACNR/B,D17716.5.123 U.MNL CONTROLNET ADAPTER - Manual (Page 38)

Planning to Use Your ControlNet Adapter Module 4–2
Publication 1771-6.5.123 – May 1996
All 1771 discrete I/O data is mapped into the processor’s I/O image
table according to the user-configurable I/O map table stored in the
processor. This image table location is specified on the ControlNet
configuration screen.
ControlNet provides significant flexibility when configuring discrete
I/O data transfers. The following are important factors to consider as
you plan and configure your system.
•
I/O is not automatically mapped into the processor’s I/O image
file based on the network address of the adapter. If you manually
configure your system, I/O from an adapter is mapped into the
I/O image file based on the I/O image file address that you enter
into your configuration. If you automap your system, I/O is
mapped into the first available I/O image space outside of the
local rack image space.
For example, if your local chassis is 12 slots and is using 1-slot
addressing mode, it will use rack numbers 0 and 1. ControlNet I/O
mapping would then start with rack 2. Note that even though the local
chassis only used 1/2 of rack 1, ControlNet I/O cannot map into any rack
number used by the local chassis.
•
Always configure your remote I/O system first. Remote I/O
devices must use the I/O image space which corresponds to their
rack number and size. A conflict could occur if you automap
ControlNet first, and it uses I/O image space which matches a
rack number on the remote I/O. Automap remote I/O first, and
then automap ControlNet, since ControlNet can use any unused
I/O image space.
•
I/O image space for a given ControlNet connection must be
contiguous. ControlNet software cannot break up a map entry
into multiple I/O image file locations.
For example, if you automap a device which requires 4 words of I/O
image table, it will map into the first available 4 word block in the I/O
image table, even if there are several 2 word blocks available prior to the
4 block area.
•
All 1771 I/O placement rules for discrete I/O module (8, 16 and
32 point) addressing still apply.
•
You can configure the adapter to scan a minimum of 0 input
words to a maximum of 32 input words in the physical rack. Data
from input modules in the chassis beyond the configured rack
size will not be sent to the processor.
•
You can configure the adapter to write to a minimum of 0 output
words to the maximum number of words in the the physical rack
(up to 32 maximum). Modules in the chassis beyond the
configured rack size will not receive outputs from the processor,
and will respond as if they were receiving all zeroes.
Discrete I/O Data Transfer
Configuring Discrete I/O
Data Transfers