Rockwell Automation 1404-M4_M5_M6_M8 Powermonitor 3000 Master Module Installation Instructions - Manual (Page 37)

Powermonitor 3000 Master Module 37
Publication 1404-IN007F-EN-P - November 2009
Native RS-485 Communication Wiring
The RS-485 communication standard supports multi-drop communication among as many as
32 stations or nodes.
The RS-485 port is also used for master module firmware upgrades in the field.
RS-485 communication wiring should be installed in a daisy-chain configuration. We
recommend that you use Belden 9841 two-conductor shielded cable or equivalent. The
maximum cable length is 1219 m (4000 ft). Use of a star or bridging topology is not
recommended and will result in signal distortion unless impedance is matched for each spur
(star topology) or network (bridge topology).
If required, install suitable terminating resistors at the ends of the daisy-chain cable. For
RS-485, install a 150
Ω, 1/4 W terminating resistor (refer to the wiring diagram). Note that
some RS-485 conversion devices are equipped with internal terminating resistors. Contact the
manufacturer of the converter for additional information.
At one end of each cable segment, connect the cable shield to the SHLD terminal of the
master module RS-485 port or the converter. The SHLD connection provides a
low-impedance ground for high-frequency noise while attenuating DC or line-frequency
signals.
The RS-485 port in the master module presents a standard load impedance to the RS-485
network, allowing the standard 32 nodes on a network.
Configuration options for the native RS-485 port include the protocol, device address, and
the data rate. Defaults are:
• auto-detect protocol.
• device address = the Device ID assigned at the factory in the range 1…254.
• communication rate = 9600 bps.
Use of RS-232 to RS-485 Converter
You need a user-supplied RS-232 to RS-485 converter for communication between the power
monitor native RS-485 port and an external device such as a computer or programmable
controller RS-232 port. Examples include:
• B&B Electronics, Inc. part number 485SD9TB (DB-9 connection).
• Allen-Bradley catalog number 1761-NET-AIC.