Rockwell Automation 20-COMM-ER 20-COMM-ER Dual-Port EtherNet/IP Communication Adapter User Manual - Manual (Page 68)

68 Rockwell Automation Publication 20COMM-UM015B-EN-P - July 2013
Chapter 4 Configuring the I/O
Limitations Using a
MicroLogix 1100/1400
Controller
Controlling I/O with explicit messages is relatively complex compared to
normal implicit I/O control.
ControlLogix and CompactLogix controllers with EtherNet/IP provide the
easiest and most integrated form of implicit I/O control for a device.
RSLogix 5000 software, version 16.00 or later, for ControlLogix and
CompactLogix controllers contains integrated profiles for PowerFlex drives
that, with a few clicks of the mouse, automatically create all controller tags
and an implicit connection at the specified Requested Packet Interval to
control the drive. This connection is monitored at both ends to verify that
the controller and drive are communicating. A watchdog will cause a drive
fault if the drive does not respond within approximately 100 milliseconds.
Therefore, using a ControlLogix or CompactLogix controller is by far the
much preferred method of controlling drives on EtherNet/IP.
If you are not using either of these type of controllers, then devices on
EtherNet/IP can be controlled with explicit messages using MicroLogix
1100/1400 controllers with the following limitations:
· An explicit message is a much slower form of control and is non-
deterministic. This means that you cannot guarantee how long the device
will take to start up or stop when the command is given. Therefore, all
equipment used in this manner should be subject to a risk assessment,
taking into account the mechanical and electrical implementation.
· A timeout value (in seconds) in the EtherNet/IP adapter will issue a
device fault if a message is not received from the controller within the
specified time. However, the controller has no way of detecting a loss of
communication to the device until the next cycle of explicit messages.
This is another factor in the risk assessment.
· Any additional devices to be controlled will require additional explicit
messages for their control, and they need to be carefully sequenced. Most
controllers have small communication queues (see the User Manual),
which need to be carefully managed if messages are not to be lost.
· Each controller has a limited number of communication connections (see
its User Manual for maximum connections), which will limit the number
of drives that can be connected.
In summary, unlike a ControlLogix or CompactLogix controller, programming a
MicroLogix 1100/1400 controller by using RSLogix 500 software with explicit
messages is more difficult, and produces a more complex program.
MicroLogix 1100/1400
Controller Example
After the adapter is configured, the connected drive and adapter will be a single
node on the network. This section provides the steps needed to configure a
simple EtherNet/IP network (see
Figure 12 ). In our example, we will configure a
MicroLogix 1100 controller to communicate with a drive using Logic
Command/Status, Reference/Feedback, and Datalinks over the network.