Rockwell Automation 1408-EMxx PowerMonitor 1000 Unit - Manual (Page 11)

Publication 1408-UM001B-EN-P - May 2008 11
Powermonitor 1000 Overview Chapter 1
DH485 Protocol
DH485 is a token-passing protocol that allows messaging by up to
32 nodes on a serial network. The master is the node that owns the
token; only the master may transmit messages. When a node has
completed transmitting messages, it passes the token to the next node.
The power monitor does not initiate DH485 data messages. When
requested, it transmits reply messages to the initiator when it gets the
token, and then passes the token to its successor.
The DH485 protocol uses the same data table addressing as DF1
protocols. Please refer to the CSP file number column of
Powermonitor 1000 data tables.
The following configuration factors have a significant effect on
network performance and should be considered when you plan a
DH485 network.
•
Number of Nodes - unnecessary nodes will slow the data
transfer rate. The maximum number of nodes on the network is
32. Fewer nodes are better.
•
Node Addresses - best to start node addresses at 0 and assign in
sequential order. Controllers may not be node 0. Initiators such
as personal computers should be assigned the lowest numbered
addresses.
•
Communication Rate - Higher is better. All devices must be at
the same communication rate.
•
Maximum Node Address - should be set as low as possible to
reduce the time it takes to initialize the network.
Ethernet Network Communication
The Ethernet network communication port allows communication
with your power monitor using a local-area-network (LAN). The
Ethernet port may also be used to view the power monitor’s internal
webpage. This Ethernet port uses a static IP address only, and can
simultaneously communicate using the protocols listed below. The
Ethernet communication port supports 10 or 100 Mbps data rate,
half-duplex, or full-duplex.
TIP
Powermonitor 1000 units only support DH485 Local Link
messages and do not support the Send and Receive Data (SRD)
messages for DH485 non-token passing slave devices.