User manual

Publication 1768-UM001C-EN-P - November 2007
40 Communicate over Networks
Modbus Support
To use Logix5000 controllers on the Modbus protocol, you will need to access
two example programs in the samples directory of RSLogix 5000
programming software that emulate the Modbus protocol. These programs are
entitled ModbusMaster and ModbusSlave. To execute these programs, you will
need to use the CH0 serial port.
For more information on these applications, see the Using Logix5000
Controllers as Masters and Slaves on Modbus Application Solution,
publication CIG-AP129
.
DH-485 Network
Communication
For DH-485 communication, use the serial port of the controller.
1768 CompactLogix controllers 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 a CompactLogix controller to act as a DH-485 interface.
By using a 1761-NET-AIC converter and the appropriate RS-232 cable
(catalog number 1756-CP3 or 1747-CP3), a CompactLogix 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.