Rockwell Automation 25B PowerFlex 525 Embedded EtherNet/IP Adapter - Manual (Page 60)

60 Rockwell Automation Publication 520COM-UM001B-EN-E - March 2013
Chapter 4 Configuring the I/O
Limitations in Using
MicroLogix 1100/1400 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 PowerFlex drive.
RSLogix 5000/Logix Designer programming software 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 ensure 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 PowerFlex drives 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 drive
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 embedded EtherNet/IP adapter will
issue a drive 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
communications to the drive until the next cycle of explicit messages. This
is another factor in the risk assessment.
• Any additional drives 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 its 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 using RSLogix 500 software with explicit
messages is more difficult, and produces a more complex program.