Allen-Bradley controllogix 1756-L55M12, User Manual

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Publication 1756-UM001G-EN-P - January 2007
Communicate over Networks 37
Additional Resources
For additional information, consult these publications:
•
Logix5000 Controllers General Instructions Reference Manual,
publication 1756-RM003
•
Logix5000 Controllers Common Procedures Programming
Manual, publication 1756-PM001
Modbus Support
To use Logix5000 controllers on the Modbus protocol, establish a
serial port connection and execute a specific ladder-logic routine. The
controller project is available with RSLogix 5000 programming
software.
Additional Resources
For additional information, consult Using Logix5000 Controllers as
Masters or Slaves on Modbus Application Solution, publication
CIG-AP129.
DH-485 Network
Communication
For DH-485 communication, use the serial port of the controller. 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 programming
software. However, excessive traffic over a DH-485 connection can
adversely affect overall performance and lead to timeouts and
decreased RSLogix 5000 configuration performance.
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. By using a 1761-NET-AIC converter and the
appropriate RS-232 cable (1756-CP3 or 1747-CP3), a ControlLogix
controller can send and receive data on a DH-485 network.
IMPORTANT
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 you
use networks in the NetLinx open architecture.