Allen-Bradley 1404-M4, User Manual

Page: 96 / 356

Publication 1404-UM001D-EN-E - October 2004
4-36 Communications
Indexed Data Table Reads using DeviceNet
Powermonitor 3000 units with optional DeviceNet communications
support only manual-indexed mode for reading large data structures
such as oscillograms, setpoint status, logs and harmonics. Refer to the
appropriate sections of this manual for detailed information.
DeviceNet Unique Write Identifier
The communications interface used in the DeviceNet communications
option is programmed to reject duplicate write messages. Because of
this, all writeable data tables in the Powermonitor 3000 include an
element called
DeviceNet unique write identifier . In many cases, your
client application may ignore this element because the message data is
unique. However, where your client application performs repeated
identical writes, it should increment the DeviceNet Unique Write
Identifier with each new message. An example of this would be
reading the Event Log or Trend Log.
Ethernet Communications Option
The Powermonitor 3000 with optional Ethernet communications
operates as a slave device on the Ethernet network. Its built-in web
server provides access to metering and status data using only your
web browser.
The Ethernet port supports up to 64 concurrent connections. It
employs an algorithm to release inactive connections after a
user-configurable time.
Ethernet communications functionality differs significantly from Series
A to Series B. Table 4.9 summarizes the differences.
Table 4.9 DeviceNet Object Classes
Class (hex) Object
01 Identity
O2 Message Router
03 DeviceNet
04 Assembly
05 Connection
2B Acknowledge handler