Rockwell Automation 20-COMM-E PowerFlex EtherNet/IP Adapter - Manual (Page 68)

4-22 Configuring the I/O
20-COMM-E EtherNet/IP Adapter User Manual
Publication 20COMM-UM010G-EN-P
Limitations Using a PLC-5,
SLC 500, or 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 PowerFlex
drive. 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 PowerFlex
drives on EtherNet/IP can be controlled with explicit messages using
PLC-5, SLC 500, or 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 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
communication 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 PLC-5, SLC 500, or MicroLogix 1100/1400 controller by
using RSLogix 5 or RSLogix 500 software with explicit messages is more
difficult, and produces a more complex program.