Rockwell Automation Publication 1756-UM001M-EN-P - February 2012 115
Serial Communication (1756-L6x controllers only) Chapter 6
DH-485 Protocol
The controller can send and receive messages to and from other controllers on a
DH-485 network. The DH-485 connection supports remote programming and
monitoring via RSLogix 5000 software. However, excessive traffic over a DH-
485 connection can adversely affect overall controller performance and lead to
timeouts and decreased performance of the RSLogix 5000 configuration.
You can also use a 1756-DH485 module to connect the ControlLogix chassis to a
DH-485 network with multiple controllers. For more information, see the
ControlLogix DH-485 Communication Module User Manual, publication
1756-UM532
.
The DH-485 protocol uses RS-485 half-duplex as its physical interface. RS-485
is a definition of electrical characteristics, not a protocol. You can configure the
RS-232 port of the ControlLogix controller to act as a DH-485 interface.
To connect the controller to the DH-485 network, you must use these
components:
• A 1761-NET-AIC converter (two controllers can be connected to one
converter)
• An RS-232 cable (catalog number 1756-CP3 or 1747-CP3) for each
controller to connect to the converter
Use Logix5000 controllers on DH-485 networks only when you want to add
controllers to an existing DH-485 network.
For new applications with Logix5000 controllers, we recommend that you
use networks in the NetLinx open architecture.
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