Rockwell Automation 1408-EMxx PowerMonitor 1000 Unit - Manual (Page 14)

14 Rockwell Automation Publication 1408-UM001D-EN-P - September 2013
Chapter 1 PowerMonitor 1000 Overview
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 When configuring serial communication, users should verify
that all serial devices wishing to communicate to the power
monitor have the same communication rate, and the same data
format.
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.